• ■-.«* / ^ « « -1 . , -. ri« ?* NLM 00103171 S SURGEON GENERAL'S OFFICE LIBRARY. Section.........— No. 113, W. D.S. G.O. no.JSA-7.3s 8—613 NLM001031715 ^International Text-Book OF MEDICAL Electro-Physics^Galvanism. FOR THE USE OF Medical Students and Practitioners. William J. Herdman, Ph.B.,M.D. A. Wilmer DuFF,M.A.,B.Sc.(Ed.). Henry McClure, M.D. George J. Engelmann, M.D. J. Mount Bleyer, M.D. Albert P. Brubaker, M.D. W. F. Robinson, M.D. Frederick Peterson, M.D. Wesley Mills, M.A., M.D., L.R.C.P. (Loud.), F.R.S. (Can.). TflO^OUGHLiV IliliUST^flTED. ^1 OF C?^\ Philadelphia : THE F. A. DAVIS COMPANY, PUBLISHERS. LONDON: F. J. REBMAN. 1895. /ArsvMLX I
A-185
By J. MOUNT BLEYER, M.D.,
NEW YORK,
Visiting Laryngologist to the German West Side Clinic, New York.
(iii)
iv
CONTENTS.
PAGE
Electro-Physiology,.........B- 1
By ALBERT P. BRUBAKER, A.M., M.D.,
PHILADELPHIA, PA.,
Demonstrator of Physiology in the Jefferson Medical College ; Pro-
fessor of Physiology in the Pennsylvania College of Dental
Surgery, etc.
Electro-Diagnosis,.........B-46
By W. F. ROBINSON, M.D.,
ALBANY, N. Y.,
Formerly Assistant to Professor Benedikt, Vienna, etc.
Cataphoresis, Anodal Diffusion, Electrical Osmosis, or
Voltaic Narcotism,.......C- 1
By FREDERICK PETERSON, M.D.,
NEW YORK,
Chief of Vanderbilt Clinic of Nervous Diseases, etc.
INTRODUCTION.
THE NECESSITY FOR SPECIAL EDUCATION IN
ELECTRO-THERAPEUTICS.
By WILLIAM J. HERDMAN, Ph.B., M.D.,
ANN ARBOR, MICH.
About ten thousand physicians within the borders of the United
States make use of electricity as a therapeutical agent daily. Many
others find occasional use for it. The surgeon and the ophthalmologist,
the dentist and the gynaecologist,—in fact, the specialist in whatever
field,—finds it a valuable aid to treatment, an indispensable handmaid. It
is the mainstay of the neurologist both in diagnosis and treatment, and
the rapid increase of exact knowledge in this branch of medical science
is largely due to the service it has rendered. The more familiar we.be-
come with the manifestations of electric energy, the more do we recog-
nize its adaptations to the requirements of disordered physiological con-
ditions. It is this lack of familiarity, on the part of the members of the
medical profession, with the laws of electro-physics and physiology, more
than any other cause, that has retarded the progress of electro-therapeutics.
Had every student during the past decade been made acquainted, during
his medical course, with the action of electric energy upon the various
tissues of the human body, and had he been instructed in the management
of such appliances as are commonly employed for controlling such energy,
there is not a general practitioner or a specialist among them who would
not be making daily use of it in his practice with increased satisfaction
to himself and benefit to his patients.
So wide is the range of adaptability of electricity to the treatment
of disease that it must become the common property of every physician,
no -matter whether his work is general or special in its nature, and, such
being the case, instruction in electro-therapeutics should have a place in
every medical-college curriculum. It is not generally understood what
such instruction requires to be of any value to the student.
It is useless for an instructor to attempt the inculcation of thera-
peutic rules in the use of electricity to a class not familiar with the
physical differences between frictional, voltaic, and induced currents;
and it is worse than useless for the members of that class to attempt the
application of such instruction to the patient if they are unfamiliar with
the management of the machinery by which such different forms of elec-
tric energy are applied. Such attempts are but doomed to ignominious
(xxv)
xxvi
HERDMAN.
failure, discouraging the physician and disgusting the patient, while the
abused agent bears the blame until better methods prevail.
To-day the practicing physician needs not to be a pharmacist in
order that he may skillfully administer his remedies, for the intermediate
work of preparation of medicines for his use is now most ably done, and
such knowledge, while it might serve a good purpose in enabling him to
detect substitutes and adulterations, would, for most practical purposes,
consume time that might be spent to better advantage. With reliable
strength and purity, his drug is furnished him in abundance ready at
hand; its dosage is simple, its physiological action comparatively uni-
form ; he need but to learn the idiosyncrasies of his patient and his course
is clear. But when employing electricity as a remedy a wider range of
knowledge is demanded. The operator must know in minutest detail
how to generate and control it, to measure and modify it, and be pos-
sessed of a manual dexterity in locating its action on the part to be influ-
enced by it. Here is a science and an art to be acquired that needs other
methods than the didactic lecture and the text-book. He must not only
be well versed in the principles that guide the physicist and skilled me-
chanic who constructs his electrical apparatus, but he must himself be
able to suggest wherein that apparatus may be the better adapted to the
special needs of his patients. He must not be dependent upon the enter-
prising but non-professional commercial agent for information as to what
form of electricity to use, and how to use it in certain cases.
The merchant has adopted the role of instructor to members of the
medical profession, and has many eager auditors. The demand for
knowledge is urgent. The schools have not supplied it. The man of
money finds it to his interest to respond to it as best he can.
It needs no further illustration or argument to show that the time is
ripe for systematic instruction in electro-therapeutics in our medical
schools. The profession at work in the field recognizes its needs. The
extensive list of disorders yielding to such treatment renders it indispen-
sable. Some medical colleges have for some time recognized its impor-
tance and necessity, and have provided for it. Others are falling into line,
and soon all will be teaching electro-therapeutics in some manner. But
how should it be taught in order that the best results may be attained.
and the science most rapidly advanced ? What ought the physician to
know who undertakes the therapeutical application of electric energy if
he would direct his treatment with an intelligent purpose and most
efficiently ?
First of all, he should be well drilled in the physics of electricity and
magnetism. By common consent among educators, such knowledge can
be best acquired by laboratory drill, where sight and touch are added to
hearing as channels for mental impress, and where the attention is
aroused and fixed with greater certainty and success. The student of
electro-therapeutics should begin with practical laboratory experience in
SPECIAL EDUCATION IN ELECTRO-THERAPEUTICS. XXvii
the management of continuous-current generators, primary batteries,
secondary batteries, dynamos and induction coils, and other apparatus
for creating electric energy and for conducting and applying it to the
body. It is just as essential for the would-be electro-therapeutist to be
brought face to face with, and to learn to overcome, the obstacles that
tend to prevent an equable and constant flow of electric energy from a
primary battery, as it is for the would-be surgeon to familiarize himself
with topographical anatomy in the dissecting-room. Such knowledge is
fundamental. There is no time for the one to consult an electrician any
more than for the other to refer to a text-book while a treatment or oper-
ation is in progress, and an emergency calling for prompt action is as
likely to arise with the one as with the other. Physics is not among the
requirements for entrance to many of our medical schools, and even
those who have had instruction in physics such as is ordinarily given in
high-schools and academies do not without a laboratory-training acquire
that manual dexterity which is indispensable for managing electric ap-
paratus successfully. Moreover, the laboratory instruction which the
electro-therapeutist requires needs to be arranged with special reference to
the problems he is to encounter. The resistances with which he has to
deal are those of the human body; the electrolysis, that of living tissue;
the range of voltage, such as can be borne without harm to vital struct-
ure. There are implements and conditions peculiar to the work with
which he must become practically acquainted. A laboratory course de-
signed to meet these requirements, and properly educate the medical stu-
dent to practice electro-therapeutics, naturally divides itself into three
divisions, by reason of the character of work pursued in each, and the
dependence of each upon that which precedes it. These divisions are:
I. Physical; II. Physiological; III. Therapeutical.
7". Physical.—The first or physical course should be arranged with a
view of presenting to the student all the practical points that are likely
to arise in the use of machines for generating static electricity, continu-
ous and interrupted currents, for medical purposes. In order to ac-
complish this, each student should be required to construct (from the raw
material, as far as practicable) his own batteries and other appliances for
generating such currents, and for applying them to the body. And
where for any reason such appliances are furnished ready-made they
should be constructed in the simplest form consistent with efficiency,
and their constituent parts left bare for inspection, if possible, so that
their action is not obscured and the principle lost sight of through any
mystery of mechanism.
The course might begin by testing the strength of currents generated
by the action of dilute acids on various dissimilar metals, by which the
gtudent will find the position which the various metals occupy in the
" contact series," and thus learn to choose those which, for reasons of effi-
ciency and economy, are best adapted for practical use in electro-thera-
xxviii
HERDMAN.
peutics. Zinc and carbon being found to meet these conditions, experi-
ments can then be made to illustrate the necessity for amalgamating the
zincs, and avoiding polarization in battery action, so as to secure a con-
stant and unvarying current. The form of cell which best meets the con-
ditions of constancy, combined with the highest electro-motive force, may
then be determined by tests of a large number of batteries, double and
single fluid, and dry. Following these tests the students should, for
their further work with continuous currents, be required to construct
zinc and carbon bichromate eight- or ten- cell experimental batteries,
which should be required to register at least fifteen volts as a test of their
accuracy in construction. After determining the electro-motive force
and the internal resistance of these experimental batteries, problems for
determining strength of currents with unknown resistances should be
solved, and then, the current being known from a galvanometer-reading,
a series of problems should be given to determine unknown resistances,
after which the body-resistances Can be tested by introducing some part
of the body into the circuit. The student should construct his own elec-
trodes for applying the current to the body. Experiments in divided
currents, shunt circuits, and joint resistances should then be undertaken,
with a view of illustrating the conditions met with in the action of
currents when traversing the various tissues of the body.
The student having thus become practically familiar with the phe-
nomena of electric generation and conduction, and the conditions that
attend them, the action of a continuous current in producing electrolysis
should then be determined by actual test on a variety of ions, the
effects peculiar to the anode and cathode distinguished, and illustrations
made of the uses for which such action can be successfully employed in
dealing with the diseased condition of the body.
The batteries arranged for generating a current suitable for heating
a cautery, and the conditions necessary for successful galvano-cautery
work, should be experimentally studied. As a part of this work, each
student should be required to make a cautery that will stand the test of
a current of eight amperes.
Induction currents should be next considered and the principle of
magneto-electric and induction machines inculcated by the construction
of temporary magnets, and a study of the phenomena they exhibit in
taking on and parting with their magnetism. An induction coil gener.
ating primary and secondary induced currents, similar to the ordinary
medical induction apparatus, should be put in the hands of each student.
It should be so constructed that its mechanism can be readily seen and
the courses of the various currents traced. With this apparatus experi-
ments can be conducted upon the body, illustrating the physiological
effects of interrupted currents of high electro-motive force on tissue-
action.
Frictional electricity should be illustrated by several forms of static
SPECIAL EDUCATION IN ELECTRO-THERAPEUTICS. XXIX
machines, and the student instructed how to operate them for therapeutic
applications.
This course of laboratory instruction would consume a period of a
longer or shorter time, according to the preparation the students, have
had in natural science, and as the requirements for entrance to our med-
ical schools advance such practical knowledge of the physics of electricity
as is here outlined might with propriety be demanded of the matriculant.
No matter where or how acquired, such preparation is indispensable be-
fore the student can with any profit undertake the work that pertains to
the remaining divisions.
II. Physiological.—Under this head should be arranged a series of
laboratory experiments designed to illustrate the manner in which the
various living tissues in animals and man respond to the electric stimulus.
No branch of medical science has had more able investigators, or
been more fruitful in yielding rich returns, than that of electro-physiology.
Such investigations have furnished a firm foundation for electro-thera-
peutics, and should be made the starting-point for practical instruction.
Yet the conditions under which experimental results are obtained in the
phj'siological laboratory differ so materially from those under which the
operator in electro-therapeutics is called upon to labor, that a physiologi-
cal laboratory training is not adequate to supply the needs of education
for the electro-therapeutist. In electric experiments in the physiological
laboratory, the result has been determined upon a decapitated or nar-
cotized animal with nerve or muscle or viscus brought into immediate
contact with the electrodes, while the physician in electric applications
deals with the human subject when the cerebral functions of his patient
are active and alert, and the skin or other structures intervene between
the electrodes and the tissue or organ to be influenced. These changed
conditions require methods of investigation peculiar to themselves. A
series of demonstrations on the human body intact and in a normal state
is^he rational prelude to attempts at therapeutical applications.
The student should first be required to obtain the normal nerve and
muscle reactions in various parts of the body with both continuous and
induced currents, noticing the amount of current required, its density,
and the points where the electrodes must be applied to get a prompt re-
sponse. This range of experiments presupposes thorough anatomical
knowledge, and reveals its necessity to the student more convincingly
than any verbal argument. These experiments can then be varied by
producing overaction in the muscle so as to weary it, and exhibit the
retardation in response to stimulus. In an animal the nerve may then
be cut, or paralyzed with curare, and the experiments repeated, exhibit-
ing the effects of injury or disease.
The student thus becomes practically familiar with the differences
in the polar action of the continuous current in exciting normal reactions
in nerve and muscle. The electrolytic action upon living tissue can then
XXX
HERDMAN.
be tested with electrodes of various sizes and material. The effect of
density upon the skin from dry electrodes is a most valuable lesson to
inculcate, since in unskilled hands the continuous current is capable of
doing serious damage to a patient, causing eschars that are extremely
slow to heal. The electrolysis of deep-lying structures should be so
conducted as to avoid wounds upon the surface from the action of the
needles employed. The manner of introducing and insulating them for
work of this kind demands experience and skill of a high order. No one
will deny that such skill should be attained before the operator attempts
it upon a patient, and that superior anatomical knowledge is here also an
indispensable requisite for safety in such operations.
Another very common use for the electrolytic action of the galvanic
current is the removal of facial blemishes, the technique of which can be
very readily acquired in the laboratory.
Cataphoresis, or the introduction of remedies into the tissues through
the agency of the anode of a continuous current, affords another field for
laboratory demonstration that is destined to prove of great value in ther-
apeutics. The range of remedies that can be thus effectively introduced
through the skin and mucous membranes for local or systemic effects are
already known to be many, and the laboratory is the proper place for
conducting such investigations as will enlarge upon and perfect this
method of medication. By employing certain of the lower animals for
the purpose, the underlying tissues can be subjected to examination and
analysis after such applications, and the result positively determined.
Or, if the tests are made upon man, the examination of the urine and
other secretions, or the evidences of the known physiological effects of
the drug, can be sought for as evidence of the efficienc}- of the method.
It is in this division of the course that the student should be instructed
in the generally-approved methods of electric applications, and be made
familiar with the physiological effects to be expected from each. Thus,
" general faradization," " galvanization of the sympathetic," " local gal-
vanization," or " faradization " of the special-sense organs, and special
systems or organs of the bod}% can be arranged as a series of experiments.
The methods and instruments employed to reach internal organs for
direct application of currents to them, as the vocal cords, Eustachian
tube, the oesophagus, the stomach, the rectum, the bladder, the urethra,,
the vagina, and uterus, all of which the student should be practiced in
before attempting actual therapeutical work, afford a wide field for gath-
ering important information and experience.
The physiological effects of frictional electricity should also form a
part of the course of instruction under this head. The cutaneous excita-
tion, the vasomotor change, the increase of circulation, and the so-called
" refreshing effects " and the sensations produced by the " electric breeze''
can be readily demonstrated, and skill acquired in the management of
electrodes for the purpose of producing them.
SPECIAL EDUCATION IN ELECTRO-THERAPEUTICS. XXXI
The student who has been through a practical drill, such as is here
outlined, will enter upon the final or therapeutical course with a prepara-
tion that will insure him against innumerable blunders, and arm him with
a confidence in the agent he is employing that is a guarantee to success.
777. Therapeutics.—The student should now have the opportunity
in the hospital wards, the operating-room, and the out-patient department
to use the information he has already gained, and learn the value of elec-
tricity in counteracting disease.
Here he learns to relieve pain, to promote absorption, to quicken
torpid nutritive processes, to excite secretion, to stimulate muscular
action, to revive nerve inactivit}^, to arrest haemorrhage, to heal ulcera-
tions, to dissipate strictures and tumors, and to cauterize and destroy ab-
normal growths by means of electricity in one or the other form with
which he has become familiar. The therapeutical work goes hand in
hand with his study of pathology and diagnosis, and he learns to recog-
nize the diseases most amenable to electric treatment and the method of
application best adapted to each. As far as is consistent with the welfare
of the patient, the student should be given the entire responsibility in
carrying out the treatment when electricity has been found to be an
appropriate remedy.
So wide is the range of disorders now found to be helped by elec-
tricity that the technique of its management in the clinic has of itself be-
come a matter of so much importance, in many of our hospitals, that a
special instructor is appointed to take charge of it. Under his direction
the student can be well drilled in all the details of its application in a
variety of diseases. The methods employed and the machinery made use
of in many of our dispensaries and hospital clinics giving electric treat-
ment are admirable, and the results all that could be desired, but the in-
struction is oftentimes of little practical value to the student when he
begins his own private work, because of his inability to duplicate or main-
tain the expensive outfit with which he has been accustomed to work, or
because any additional information which he may seek to obtain from
other sources is couched in language which he does not clearly comprehend
by reason of the difference in terms and methods of treatment adopted by
those who practice electro-therapeutics. A disparity of results arises
also between those who employ electricity in practice, because of a lack
of uniformity in the apparatus employed. The rapid advances which all
who are personally familiar with the capacities of electricity in one or
other form as a curative agent know it to be capable of making are greatly
retarded by this lack of uniformity in method and machinery. Electro-
therapeutic apparatus can be reduced to much greater simplicity and
still retain all the efficiency that it has been shown to possess. Primary-
and secondary- current batteries, medical induction coils, milliampere-
meters, rheostats, and dynamo-current controllers for medical uses should
be made in accordance with standards adopted or approved by the com-
xxxii
HERDMAN.
mon consent of those who have proved by their work the value of such
patterns. When it is possible to report the treatment by electricity of a
well-known pathological state in terms of exact dosage by standard in-
struments,—all of which is within the range of possibility,—then electro-
therapeutics will have reached a stage when its claim to be recognized as
an exact science will be far in advance of many other branches of med-
icine, and the art will keep pace with the progress of the science.
ELECTRO-PHYSICS.
By A. WILMER DUFF, M.A., B.Sc. (Edin.).,
LAFAYETTE, INDIANA.
1. Purpose and Plan of this Section.—There are always two ways
in which a scientific instrument can be used,—the blindly mechanical and
the intelligent. In the former the employer of the instrument follows
certain rules laid down for its use by the inventor, or some one who
knows more of its nature and construction. In the latter the employer
is constantly verifying and modifying the rules of thumb supplied with
the instrument in accordance with what he has learned of its inner
mechanism and principle of action ; that which Clerk Maxwell, in his
childish questionings, called the " go " of the thing.
Now, this first section is intended chiefly for the intelligent medical
man who, just as he desires to know the chemical constitution of the
drugs he prescribes, desires also to know all that can be acquired without
undue labor of that agent—electricity—that has come to be one of his
most important tools. Specialists in medical subjects will treat of the
different sections under which electrical phenomena have been grouped
(voltaic, faradic, franklinic), and will do so from the point of view of
their medical applications; and it is considered that a connected view
of the whole subject, showing the relations of those great parts and
sketching in the intervening districts, will serve the reader as a prelim-
inary view of a strange cit}r from a high eminence serves the intelligent
traveler before he descends to plunge into the labyrinth of streets.
While an attempt will be made to treat all the fundamental principles
of the subject in a simple and easily intelligible way* yet those parts
which are most pertinent to medical applications will be treated more
fully than less pertinent parts. Especial care will be taken to define
and explain technical terms, while less attention will be given to the
details of experimental methods and apparatus.
To save frequent digressions in the treatment of electricity itself a
concise statement of some parts of general physics is prefixed, and will
be referred to, as occasion arises, at different points.
2. Process or Physical Advance.—When attempting at the end of
this section to explain what electricity is, what shall we mean by such
an explanation ? What we mean is, that we shall bring it into line with
other more familiar, though perhaps equally unexplained, facts. This is
the process of physical explanation,—the reduction of two problems to
one. Thus, we shall attempt to show that ordinary mechanical prin-
ciples and the medium called the ether postulated by light suffice to
explain electricity.
(A-l)
A-2
DUFF.
3. Matter and Energy the Only Real Things in the Physical
Universe.—In discussing what electricity really is, we shall be con-
fronted by the question, What is the test by which we distinguish between
things existing in and by themselves and mere relations between things,
or between things and us,—that is, ways in which we view things ? The
former are objectively existent things, the latter merely appearances,
and they stand to each other as a landscape to a mirage. Now, the test
we adopt is this : A thing does not change in total quantity,—there is no
likelihood of the landscape disappearing utterly, whereas the mirage may
vanish into nothing; in other words, one-is conserved, the other is not.
Thus, we take as our test conservation, i.e., the property of always
remaining the same in quantit}'.
If, now, with the touch-stone of conservation we try things around
us, we shall find that there are but two real things, viz., matter and
energy; for each of these is conserved or never varies in quantity.
Even force is not a thing, for with a Bramali press or a lever we can, by
the exertion of the smallest force, produce the greatest force desirable,
and then make it vanish as rapidly. But while matter and energy agree
in being conserved, we shall find them differing in a marked way. Each
appears in a variety of forms: matter as oxygen, hydrogen, carbon,
etc.; energy as mechanical energy, heat, light, sound, and electrical
energy. The difference is, that whereas no one form of matter ever (so
far as we know) changes to any other form, on the other hand, any one
form of energy can change to any other form, its quantity still remain-
ing the same. Hence we say matter is untransformable, while energv is
highly transformable. Energy, in fact, only manifests itself in the
process of transformation. Its transformability is the life of the physi-
cal world, matter its body.
4. Combinations of Different Forms of Matter—Terminology.__
At the present time about seventy different forms of matter or chemical
elements are known, no one of which can, so far as we.know, be trans-
formed into any other. But they are capable of uniting two, three, four,
etc., at a time, to form compounds differing markedly in properties from
the elements. Hydrogen and oxygen are ordinarily gases, but by uniting;
they form a liquid,—water. This tendency to unite is called chemical
affinity, and a side-result of electrical advance has been to give a highly
probable explanation of this affinity.
Many things indicate that any quantity of one form of matter really
consists of very small particles, which, so far as we know, are indivisible
and are hence called atoms. All the atoms of any one form of matter
are absolutely alike, and chemical compounds are formed by the union
of unlike atoms. Hence the smallest part of a compound is reallv a
group of unlike atoms, and this smallest particle is called a molecule.
In the union of atoms to form molecules a remarkable diversity
shows itself, and will be referred to later. Such unions are not always
ELECTRO-PHYSICS. A-3
monogamous ; many are bigamous, trigamous, etc. Oxygen is a highly
active bigamist; so that when an oxygen atom unites with monogamous
hydrogen atoms to form water it requires two, which is indicated by
representing the compound molecule by H20. Again, a nitrogen atom
takes three monogamous atoms, and so on. This combining capacity
of an element is called its valency, and atoms are spoken of as uni-
valent, divalent, trivalent, and tetravalent, or are called monads, dyads,
triads, and tetrads.
If, now, we chemically separate such a compound as H20 into its
constituents, the H atoms unite two at a time, to form H molecules, and
the 0 atoms two at a time to form 0 molecules. But just at the moment
of rupture, before this recombination, the atoms are open to accept
other partners than ones of their own kind, and hence are at that time
in a specially active state as regards readiness to act on foreign bodies.
For an obvious reason this is called the nascent state.
5. Physical Constitution of Matter—Kinetic Theory.—No very
accurate determination of the sizes of molecules is possible yet, but a
very rough approximation has been arrived at by Sir Win. Thomson (now
Lord Kelvin) from four different points of view. It turns out that in
ordinary liquids and solids there are somewhere between five million
and ten billion molecules per inch of length,—that is to say, the centres
of two adjacent molecules are separated by something between one-
five-millionth and one-ten-billionth of an inch. In a gas the number
altogether depends on the density of the gas, and can be reduced to
any desired extent by reducing the density of the gas by means of an
air-pump. What the actual size of the molecules are, compared with
the distance between their centres, we do not know, but certainly it
can onlv be an exceedingly small fraction of that distance.
The progress of research has afforded conclusive evidence that these
ultimate particles are not at rest, but are continually in most vigorous
motion however rigid the mass of the substance may be. This motion
is of several different kinds :—
(a) Translation of molecules,—that is, motions by which the molecules move from
place to place without any tendency to return. The velocity of this translation may vary
widely, and bodies are classified with reference to it into :—
1. Gases.—Bete the particles continue moving in straight lines until they collide
with other particles or with the sides of the containing vessel, when they rebound in
new directions. Thus the particles act as quite separate individuals. The velocity of
translation in a gas is, on the average, about one-half greater than that of sound in the
gas ; in the air it would amount, under ordinary conditions, to about 1630 feet per second.
This velocity accounts for the great readiness with which two masses of different gases mix
when the containing vessels are brought mouth to mouth. The frequency of collision
between particles can also be calculated by indirect methods, and also the mean free path,
or average distance traveled by a particle between two successive collisions. In the case
of hydrogen at atmospheric pressure, the collisions take place at about the rate of 17000
per millionth of a second, and the mean free path is, roughly, four-milliontlis of an inch.
But a gas can be rarefied until the mean free path amounts to several inches.
2. Liquids.—Here the particles still have motionB of translation, but they are exceed-
A-4
DUFF.
ingly small compared with the preceding. Their existence, however, is shown by putting
a layer of colorless solution (or water) on a solution of a colored salt {e.g., copper sul-
phate) and noticing that the two gradually mix by diffusion, as it is called.
3. Solids.—Here the velocity of translation is nil,—not that the particles are at
rest, but they never get far away from their mean positions.
(6) Vibration of Molecules.—By. this we mean a rapid to-aud-fro motion in some way
or other, such as not to carry a particle far away from its mean position, but to keep it con-
tinually moving to and fro around or through it.
(c) Rotation of Molecules.—By the indirect impact of molecule on molecule, or by
some other means, the particles are set into to-and-fro rotations, or it may be continuous
rotations.
(d) Oscillation of Atoms in Molecules.—Finally, the atoms in a molecule are in violent
oscillation in a number of ways ; and by different means (e.g., heat) these oscillations may
be increased in violence until the atoms part company and the molecule is dissociated. The
rapidity of these motions can be readily determined from the color of light to which they
give rise. It is very great. For instance, an atom of sodium oscillates in three different
ways,—at the rates, respectively, of 4.5 hundred million, 6.1 hundred million, and 6.9
hundred million times per millionth of a second.
6. Effects of Motion of Molecules.—One of these, diffusion, has
been referred to above. Another is what has been named osmosis.
When pores exist in a membrane in contact with a fluid, some of the
rapidly-moving particles will penetrate and pass through. Now, the
molecules of different liquids are moving at different rates, and also are
probably of different sizes, and hence will pass through such a membrane
at different rates ; so that, if such a membrane separate two different
liquids, more of one will pass through than of the other. Hence there
will be a rise of fluid on one side and a fall on the other. This is called
osmosis. For example, if a vessel full of alcohol and closed by bladder
be immersed in water, the contents of the vessel will soon increase so
much as to burst the bladder. If, on the other hand, the vessel contain
water and be immersed in alcohol, the bladder will contract. (For similar
effects produced by the electric current see § 60.)
A further effect of the vigorous motion and consequent violent
collision of moving particles is that some are ruptured and their con-
stituent atoms separated. They do not, however, long remain separated
but rapidly find partners among similarly dissociated atoms. Above a
certain temperature, called the temperature of dissociation, the rapidity
of dissociation may exceed that of recombination, and then the fluid is
as a whole, dissociated. The former, or temporary dissociation, at
ordinary temperatures, is of great importance in the explanation of elec-
trolysis (§ 61). That such a process is continually going on is evident
from the fact that if two salts are dissolved and then mixed new bodies
being different combinations of the atoms of the two salts, are frequently
formed, and, being insoluble in the mixture, are precipitated ; and this
effect takes place even if the new compound is a less firmly united
combination than the original salts.
Y. The Form of Matter Called the " Ether."__We know any
form of matter merely as an inference from the phenomena of our sense.
ELECTRO-PHYSICS.
A-5
Now, a number of phenomena receive their only explanation by the
assumption of a veiy exceptional form of matter called the ether. The
evidence of its existence is therefore quite of the usual kind. Though
its existence can hardly be regarded as doubtful, all the theories of its
constitution are still pure speculation. Some of its properties to which
we shall refer are :—
(1) It permeates all bodies and pervades all known space, even to the most distant star.
(2) It is affected by the matter of bodies in which it is. It appears to be concentrated
in it to an extent depending on the density of the matter. Ether thus bound differs from
free ether, in that it transmits short waves more slowly than long ones.
(3) It is continuous, not granular.
(4) Its density is to that of water as is unity to unity followed by twenty naughts
(1020), while its rigidity is one-billionth that of steel.
Light consists of transverse vibrations in the ether, and the rate of
transverse vibration in a medium is greater the greater its rigidity and
the less its density, just as the rate of vibration of a tuning-fork depends
on the ratio of its rigidit}' to the massiveness of its prongs. Now, small
as the rigidity of the ether is, it is immensely great compared with its
density. Hence the immense rapidity of the vibrations constituting
light,—for red light about four hundred millions per second.
Again, if the ether fills all space and is, in some respects at least,
like an elastic solid, how are the heavenly bodies not retarded by it?
Stokes has given a satisfactory answer, but space will only permit us to
give Sir Wm. Thomson's suggested analogy : Shoemakers' wax will offer
great resistance to the passage of anything through it, but bullets will
pass down through it and corks float up through it, provided sufficient
time be given them; the slower their motion, the less the resistance.
Similar^, may it not be that the motion of the heavenly bodies is im-
mensely small compared with the resistance of the ether?
8. Energy, Kinetic and Potential.—We now come to the second
constituent of the physical universe. By energy we mean the power of
doing work. Now, power of doing work resides in bodies in either of
two states: (1) in virtue of their motion, e.g., cannon-balls in motion will
batter down a wall; (2) in virtue of their shape or position, e.g., a wound-
up spring will make a clock go, while a stretched spring or elastic band
can, by contracting, pull up a weight. The former kind, or energy of
motion, is called kinetic energy; the latter kind, or energy of shape or
position, is called potential energy.
Measures of Energy.—The work a moving body can do is found to
vary directly as the square of its speed, and also, of course, as its mass,
and is taken as^mV2. The work a deformed system can do is the
force it can exert into the distance through which it can exert it, or Fs.
As these are interchangeable, whenever one passes into the other the
principle of the conservation of energy requires that
Fs = imV2
A-6
DUFF.
9. Energy of Vibrations and Waves.—In some kinds of mechan-
ism we have a regular change of the whole energy from the kinetic to the
potential form, and back again to the kinetic form, and so on. A simple
pendulum gives an example of this. At the highest point of its swing
it stops, and just at the moment has no velocit}r, and hence no kinetic
energy. Its energy is all potential,—i.e., it is raised up and could, in
virtue of its weight, do work in descending. Again, at its lowest point
its potential energy is reduced to a minimum, for it can get no lower,
and what it has lost in potential energy has been transformed into
kinetic energy. At intermediate points its energy is partly potential
and partly kinetic.
The same is true of any kind of vibration or to-and-fro motion,
whether to-and-fro motion in a straight line or to-and-fro motion of rota-
tion, such as that of the balance-wheel of a watch.
When a vibration is handed on from part to part of a medium, each
part of the medium being set into vibration as the disturbance reaches
it, we have what is called a wave,—e.g., an up-and-down motion started
at the end of a rope will be transmitted along the rope, giving rise to a
succession of waves. Hence, by the above, if we fix our attention on
any part of the medium in the course of the waves, its energy will
periodically change from all kinetic to all potential and back again ; but
if we consider a whole wave, at the crest and trough (i.e., the places of
greatest displacement) the energy will be all potential, but at the mean
level the energy will be all kinetic, and at intermediate points the energy
will be partly kinetic and partly potential. Considering a whole wave-
length at any time, the energy will be half kinetic and half potential.
10. Subdivisions of Energy.—Though all energy we feel convinced
is one, as is shown by the interchangeability of its different forms, }^et
the energy manifested in different classes of phenomena has received
different names :—
(1) Mechanical Energy.—In such cases as the moving cannon-ball and wound-up or
stretched spring, already mentioned, the energy is obviously due to the relative motion or
position of the parts, and so may be called mechanical energy. Other kinds of energy are
in reality equally mechanical, but not so obviously so, and hence are not so denominated.
(2) Energy of Waves of Sound.— Waves may exist in any medium, and such always
possess energy. For example, water-waves can do work in the destruction of a break-
water. Sound consists of waves of compression and dilatation in the medium conveying
the sound. Its energy is, accordingly, half kinetic and half potential.
(3) Energy of Heat in Matter.—A hot body can do work, as, for instance, by boiling
water and working a steam-engine. Hence it possesses energy. In what form does this
energy exist ? We can say at once that it is energy of motion of the particles and of the
ether in contact with the particles. The translational part of their motions gives, of
course, kinetic energy, and the vibrational part varies between the kinetic and potential
forms.
(4) Energy of Light Waves in the Ether.—Waves in the all-pervading ether, consisting
of vibrations transverse to the direction in which the waves are traveling, are called light and
radiant heat, going by the former name when the wave-lengths lie between -^^ inch and
rdm inch> and DV tne latter name when the wave-length lies outside of those limits. But
ELECTRO-PHYSICS. A-7
we may use the word light in the wider sense, so as to include both of the above divisions.
Here, just as in the case of sound, the energy of the waves is half kinetic and half
potential.
(5) Energy of Gliemical Affinity.—Dissimilar atoms unite to form molecules in virtue
of an attractive force between them. This force is called chemical affinity. This force of
chemical affinity is too slight for consideration until the particles come within a certain
range of one another, and then it comes into play and draws them together. Now, when
such dissimilar atoms unite, the force is exerted through a certain distance, and hence
does work. When work is done, energy is spent and reproduced in a different form ; so that
two uncombined atoms having a chemical affinity for one another form a system having
potential energy. On combination this energy re-appears, either as heat energy, or light
energy, or sound energy, or electrical energy. To separate the molecule again into its con-
stituent atoms requires just the amount of energy that they yield up on combination, and
when separated they will have just their original amount of potential energy.
(6) Electrical and Magnetic Energy.—At the close of this section we shall state the
most likely theory as to the nature of these forms of energy.
11. Fundamental and Derived Units of Measurement.—Any
property of a body, if estimated numerical!}', must be so estimated by
comparing it with a standard or unit of the same kind. Now, all bodies
occup}' space and possess mass, and hence we must have units of space
and mass. If we have to consider motion or change of any kind the
element of time will enter. The units of length, mass, and time are the
fundamental units, and may be arbitrarily taken as anything we please.
The English have chosen the pound, the foot,and the second, being fixed
by arbitrary definition. The French have chosen the centimetre, the
gramme, and the second, equally arbitrarily defined. These French units
are the most convenient because they are decimally subdivided and mul-
tiplied, and hence are the ones usually employed for scientific purposes.
They are shortly denoted as the C. Gr. S. system. For translating from
one system to the other the following values may be usefully remembered :
A metre = 100 centimetres = 39.37 inches; or an inch = 25.4 milli-
metres = 2.54 centimetres. Again, 1000 grammes make a kilogramme.
Half of the latter, called a demi-kilo, is the ordinary commercial retail
standard used in France, and is roughly equal to a pound,—more exactly,
= 1.1 lb. Hence a gramme = .0022 lb.
Derived Units.—For measuring other properties, units derived from
the above are employed. The unit of velocity is a velocity of unit
length per unit time, or, in the C. Gr. S. system, a velocity of a centi-
metre per second. Acceleration is the rate of increase of velocity, and
the unit of acceleration is, therefore, defined in terms of the unit of
velocity and the unit of time. It is an increase of unit velocity in unit
time, or, in the C. Gr. S. system, an increase every second of a velocity
of a centimetre per second. A force is whatever produces or changes
motion in matter, and hence the unit of force is defined in terms of the
units of acceleration and mass, as the force which produces unit accel-
eration in unit of mass. In the C. G. S. system it is called the dyne.
The dyne, therefore, is a force which every second increases the velocity
of a gramme mass by one centimetre per second, or, stated more briefly,
A-8
DUFF.
gives a gramme mass an acceleration of one centimetre per second per
second. Work is done when a force acts through some distance, and is
measured in terms of the force exerted and the distance through which
it acts. The C. G. S. unit of work, or the work done by a dyne when
exerted through a centimetre, is called the erg.
12. Subdivisions of Electricity,—For convenience of treatment
electrical phenomena have been divided into three departments: (1)
static (or franklinic) electricity, (2) kinetic (or voltaic) electricity, (3)
induced (or faradic) electricity. In addition to these there is the sub-
ject of magnetism, which will be treated of between (1) and (2).
Static (or Franklinic) Electricity.
13. Definition.—As our ideas are still very dim and vague as to what
electricity is, we can at the outset only define the thing we are going to
study as that which is made manifest in a certain way and has certain
properties. If a dry glass rod be rubbed with silk it is found to have the
property of attracting light bodies such as pieces of paper and bits of
pith. That which is made manifest by this rubbing, whether it is a
thing, or a state, or whatever it is, we call electricity, and the rod is said
to be electrified. But if we try a number of different substances to rub
the glass with, or a number of different solids instead of glass to be
rubbed, we shall find the same thing true. In all cases electricity is man-
ifested. For example, we shall find the property strong when the rubber
is of flannel and the stick of sealing-wax.
14. Two Kinds of Electricity.—So far as its action on light bodies
—say, a pith ball suspended by a silk string—is concerned, we shall find
the electricity shown in all the above cases quite the same. The pith ball is
in all cases first attracted by the electrified glass, touches it, and is then
repelled by it. The same is true of the electrified sealing-wax. But a
difference will soon be discovered. It will be found that after touching
the glass the pith ball is repelled by the glass but attracted by the
sealing-wax, and after touching the sealing-wax it is repelled by the
sealing-wax but attracted by the glass, so that it may be made to vibrate
between the two.
Hence we are compelled to recognize two kinds of electricity. These
are often called vitreous (like that found on glass after rubbing by silk)
and resinous (like that found on sealing-wax after rubbing by flannel).
There are no more than two kinds, for the electrified pith ball is in all
cases either attracted or repelled by an electrified body. When we come
to discuss what the real nature of electricity is we shall find that there
may really be only one kind ; that, in fact, electricity is a thing, and that
vitreous and resinous only describe different states of that thing. A
very old theory associated with the name of Franklin is that the vitreous
form is merely an excess of that thing and the resinous a deficiency^ of
it; and so another pair of names have arisen, namely, positive instead of
electro-physics. A-9
vitreous and negative instead of resinous. Though not committing our-
selves in an}r way to this theory, we shall usually employ these terms,
positive and negative, for in another respect they are specially happ}r
terms. In algebra positive and negative are opposed terms and mean
that two quantities of the same size, one being positive and the other
negative, when simply added together amount to zero. We shall find
the same true of the two electricities after we have defined what we mean
by a quantity of electricit}^.
15. Hypothesis Provisionally Adopted.—We do not stop here to
settle whether all electricity is of one kind or whether there are two
kinds. The former theory, stated b}' Sir William Watson and elab-
orated by Franklin, is called the " one-fluid " theory. The latter, asso-
ciated with the name of Sumner, is called the " two-fluid " theory. Its
terminology is the most convenient for the description of electrical phe-
nomena, and we shall adopt it as our working hypothesis, though we shall
altogether avoid the term fluid and simply speak of two kinds of elec-
tricity. To state it at fuller length, it is this :—
(a) There are two kinds of electricity.
(b) Like kinds repel each other, unlike kinds attract each other.
(c) An unelectrified body contains equal quantities of the two kinds,
inexhaustibly large, and these two kinds can be separated, to a greater
or less extent, by friction or the action of other electrified bodies.
(d) The attractions and repulsions mentioned in (b) are weaker the
greater the distances between the electrified bodies. (More precisely,
they decrease in proportion as the square of the distance increases.)
The explanation this theory gives of the pith-ball experiments is
the following : When the electrified glass rod is brought near to the
pith ball, the positive electricity of the rod separates the combined elec-
tricities of the pith ball, attracting the negative and repelling the positive
in accordance with (6), so that the side of the ball nearer the rod is nega-
tively and the side farther away positively electrified. The negative
charge being nearer the rod than the positive one is, by (d), more strongly
attracted than the positive charge is repelled, and the final result is
attraction.
Induction.—This separation of the electricities of an unelectrified
body by the action of an electrified one is called induction. On touching
the rod the negative electricity of the ball is neutralized by an equal
quantity of the positive of the rod, and so the ball is left positively
charged. To explain the action of an electrified sealing-wax rod on a
single pith ball we have only to interchange the words positive and nega-
tive in the above. After contact with the glass rod the pith ball is
positively charged, and hence is attracted by the negatively-charged
sealing-wax. In the above it has been assumed that equal quantities of
the two kinds of electricity are always produced. This will be referred
to later, and experimental proof given (§ 17).
A-10
DUFF.
+
^C
r*s
A
16. The Gold-Leaf Electroscope.—A much more convenient appa-
ratus for detecting the presence of electricit}' than the pith ball spoken of
is a pair of strips of gold-leaf hung from a metal rod inside of a glass jar,
the metal rod having a metal disc at the top. This is a sensitive instru-
ment for indicating the presence of electricity and testing its kind ; for,
on bringing an electrified body over the disc the electricities of the disc
are separated, unlike electricity being attracted by the electrified body
and like electricity .being repelled to the gold-leaves. The leaves accord-
ingly, being similarly charged, repel one another, and therefore diverge.
This divergence will be greater the greater
*-----------——\ g the electricit}^ repelled to the leaves ; that is,
the greater the charge of the bod}r being-
examined. Thus, the instrument is a de-
tector of electricity.
Further, it can be used to test the nature
of a charge ; for, if while it is subject to the
inductive influence of a charged body the
plate, C, be touched Iry the hand, the leaves
immediately collapse. The explanation of
this is, that the charge of the leaves escapes
Fig. 1. through the hand, while the charge on the
plate is still kept " bound " by the attraction
of the charged body which is being tested. Then, wTien the charged body
is removed, the charge formerly " bound " on the plate is set " free " and
spreads over the leaves also, so that they again diverge, but this time
with electricity of the opposite kind to that of the original inducing
charge.
Now, to test a charge by the electroscope : Suppose the inducing
body, B, was positively charged, then the final charge of the leaves was
negative. If, now, a negatively-charged body be brought near the plate,
it will repel still more negative electricity to the leaves, and so cause
them to diverge still more; but if a positively-charged body be brought
near the plate, it will repel positive electricity to the leaves, and so cause
them, at first at least, to diverge less. If, however, the positively-charged
body be sufficiently strongly charged, it may just repel enough positive
electricity to the leaves to neutralize their negative charge, so that they
collapse; and then, when brought still nearer, it will repel still more posi-
tive electricity to them, so that they again diverge, but this time with
positive electricity. Thus, it is the initial movement of the leaves that
must be observed.
Hence, when the leaves are left negatively charged, they will expand
more when a negative charge is brought near the disc, C, but less when
a positive charge is brought near it.
17. Equal Quantities Simultaneously Developed.—By means of
the above delicate instrument we can prove the point referred to at
ELECTRO-PHYSICS.
A-ll
the end of § 15. A flannel cap is made for a rod of sealing-wax. A
dry silk thread attached to the cap enables us to turn the cap without
touching it. If the rod be turned inside the cap, and then drawn out and
presented to the electroscope, it will be found to be negatively electrified ;
the cap, on being presented to the electroscope, will be found to be posi-
tively electrified. But if the rod be turned several times inside the cap
and then, without drawing the cap off, both together be presented to the
plate of the electroscope, no effect on the leaves is observed. Hence, the
two electricities are developed simultaneously and in equal quantities;
and this is found to be always so.
18. Electricity Obtainable from All Bodies.—Having shown that
as an effect of rubbing in certain cases equal quantities of the two kinds
of electricity are obtained, the question arises, Is it only from a limited
number of bodies that electricity can be so obtained ? Apparently so;
for a metal rod rubbed will show no effect on the electroscope. But may
it not be always developed bv rubbing, and in some way escape our
notice ? May it not leak away before being noticed ? Through what
substances will electricity leak? This can be most readily tested by the
electroscope : having charged it, touch it with the finger; the charge
escapes. Touch it with a metal wire; the charge escapes. Touch it
with a dry silk thread ; the charge does not escape. Wet the silk thread ;
it escapes. Try a dry glass tube, it does not escape; try a linen thread,
and it does escape. Hence, electricity moves along some bodies, not along
others. The former are called conductors, the latter non-conductors or
insulators.
This naturally suggests that a metal rod, if insulated and rubbed,
would be found electrified. Such will be found to be the case; for, if a
brass rod be attached to a glass handle and rubbed, it will affect the
electroscope. Electricity, in fact, can be obtained by the friction of any
two bodies, though stronger charges will be obtained from some pairs of
substances than others.
But we can go farther than this. We can arrange all substances in
regular series, a glance at which will tell us what will happen if we rub
any two substances in it together. This series is called Volta's contact
series. It is such that if any two substances in it be rubbed together,
the one that comes higher in the list will be positively electrified and the
other negatively. The following will illustrate what is meant :—
+ Catskin. I Cotton. Sulphur.
Flannel> ^ gilk. Gutta-percha.
Ivory. ' Metals. —Gun-cotton
Rock-crystal. Sealing-wax.
Glass. Resin.
I
19. Conductors and Non-Conductors.—These are only relative terms.
No absolute non-conductors are known and no perfect conductors. But
when we have defined conducting power more exactly we shall find a
A-12
DUFF.
great difference between substances as regards their conducting powers.
Hence bodies that conduct well are called conductors, and those that
conduct so extremely ill that under ordinary circumstances they may be
regarded as devoid of conducting powers are called non-conductors or
insulators.
The following are conductors : Metals, graphite, flame, linen, cotton,
moist bodies generally, etc.
The following are non-conductors: Ebonite, resins, shellac, amber,
caoutchouc, dry gases, sulphur, glass, silk, wax, etc.
20. Machines for Obtaining Electricity by Friction and Induc-
tion—The Electrophorus.—Having thus the means of obtaining elec-
tricity in small quantities, all we need to get a good continuous supply is
to apply mechanical devices to working these sources of electricit}'. Full
descriptions of these machines and their treatment will be found under
the section treating of " Franklinic Electricity," to which the reader is
Fig. 2. ■+■ -+■ ~\---»- '
Fig. 3.
rr^
A
Fig- 4. Fig. 5.
referred. The principle on which they are all founded will be readily
grasped from the following brief description of the very simplest of
them,—the electrophorus.
The electrophorus consists of a shallow pan of metal (called the sole)
containing a cake of wax (resin or ebonite), and a circular disc of metal
of somewhat smaller diameter than the pan, and provided with an insu-
lating handle. This is called the cover. It is used as follows:—
(1) The cake is dusted with a piece of flannel, after which the surface of the cake
is found to be negatively electrified, and by induction a positive charge is drawn to the
metal of the sole. (Fig. 2.)
(2) The cover is now brought down on the cake, and thereby a positive charge is
induced on the metal cover. (Fig. 3.)
(3) The cover is now touched with the finger, whereupon the repelled negative charge
of the cover escapes. (Fig. 4.)
(4) The cover is now removed and carries away a positive charge with it, leaving the
cake exactly in its first condition, making allowance for a slight amount of leakage of its
charge that has nothing to do with the process. (Fig. 5.)
All we need to do now is to mount the cover and sole on rotating
plates in such a way that when the plates are rotated, by hand or other-
wise, the cover is brought into the presence of the sole, touched, to carry
ELECTRO-PHYSICS.
A-13
away its repelled charge, and then carried around to another body, to
which it imparts its charge, and again brought around in front of the
sole. Thus we shall have a continuous electrophorus yielding supplies of
both kinds of electricity.
An important point may be noticed in the foregoing description. The
charged cover when removed contains a stock of energy, as is shown by
the noise and sparks it will yield on giving up its charge to another
body. Whence came this energy? Not from the cake, for its charge is
not at all diminished by the operations. To produce energy work must
be done or energy expended. The source of the energy of the charged
plate is the extra work that must be done, in lifting the cover away from
the oppositely charged cake, over and above what would be done if the
cake were not charged. Similarly, in a continuous machine more work
is done in rotating the parts when the machine is charged and working
than would be done if the machine were not charged, and this extra work
is the source of the energy.
The above must not be understood as implying that electricity is
energy. It is not, though electrification is. But, of this later.
Fig. 6.
21. Distribution of Electricity on Conductors.—On a non-con-
ductor electricity remains where developed, but on a conductor it spreads
itself, though not uniformly. The charge on a small part of the surface
is greater the more curved it is. The charge per unit of surface is what
we define as the surface density of the electrical distribution. It will be
noticed that we speak only of the surface density, and in truth this is all
that we need speak about, for electricity resides only on the surface of
conductors. No charge whatever can be detected, except on the surface.
The charge of electricity a conductor will accept depends in no way on
how the interior of the conductor is constituted, whether it be hollow
or filled in any possible way. This can be shown in many ways. Biot
showed that when a ball is charged and covered by two metal hemi-
spheres with insulating handles, then, after the hemispheres have
touched the ball and been removed, no charge remains on the ball.
Faraday proved it by showing that if a small, conical net be charged
and then turned inside out by means of a silk thread through the vertex,
the charge always resides on the outside.
22 The Static Unit of Electricity.—Electricity is that which pro-
duces certain attractions and repulsions, and is to be therefore defined
in terms of the force of these attractions and repulsions. Let us think
of two equal quantities of positive electricity at two points a unit dis-
A-14
DUFF.
tance apart, and let these quantities be such that they repel each other
with a unit of force. Then, either of these we shall take as our unit of
electricity ; or, the static unit of electricity is such a quantity that when
at unit distance from another equal quantity it repels the latter with unit
force.
23. The Electrical Field.—An electrical field is the portion of
space in the neighborhood of electrified bodies considered with reference
to electrical phenomena. At every point in an electrical field there is an
electrical force,—i.e., a small charge of electricity introduced there
would be urged with a definite force in a definite direction. The force
with which a positive unit would be urged is called the electrical force or
the field-strength at that point. To specify fully the force at a point in
the electrical field, we must give both the magnitude of the force and
its direction. If, starting from any point, a curve be drawn following
everywhere the direction of the electrical force at the points through
which it passes, such a curve is called a line of electrical force; or, a line
of electrical force is a line whose direction at every point is that of the
electrical force.
24. Potential.—The conception of potential is one of the most im-
portant in the treatment of electricity. Unfortunately, it is also one
that has acquired the reputation of presenting considerable difficulty to
the uninitiated. This evil reputation it probably owes to a certain con-
fusion in the way in which it is frequently explained. To understand it
clearly we must remember clearly the difference there is between the idea
or meaning of a physical propert}' and its measure. The idea can be
but one, though the modes of measurement may be man}'.
To make clear what we mean let us think of the word mass. By the
mass of a body we mean simply the quantity of matter it contains. But
when we proceed to measure the mass we may employ several methods.
We may compare masses by comparing the speeds that a certain force
—say, a stretched elastic string—drawing them along a smooth horizon-
tal table will get up in them. Then, by a well-known law due to Newton,
the masses are inversely as the speeds thus produced by the same force.
Again, we may compare the masses by comparing the forces with which
they are attracted by the earth. Thus we measure them by weighing them
in a balance. These methods lead to the same result, and are there-
fore consistent. Others might be given, but these will suffice to make
clear the distinction referred to.
Let us take another and more closely parallel case, viz., temperature.
The idea of temperature is simply this: Of two bodies, that is said to be
at the higher temperature which will yield up heat to the other when the
two come into contact; or, temperature is that quality which determines
the direction of flow of heat when two bodies are put in contact. Now,
we may measure this property in various ways,—e.g., the higher the tem-
perature of a mass of mercury, the greater is found to be its volume
ELECTRO-PHYSICS.
A-15
Hence we compare temperatures by the height to which mercury rises
in a closed tube. This is the method of the mercury thermometer.
Again, if we take a spiral spring made out of a ribbon, consisting of a
strip of platinum and a strip of silver, it will be found that the higher its
temperature the more it will untwist, and so turn a light needle, which
will indicate the temperature. Thus, temperature bears but one mean-
ing, but the propert}^ can be measured in different ways.
The idea of potential is like that of temperature, viz., the quality
that determines the direction of flow of positive electricity when two
charged bodies are brought into communication by a conductor. The
one from which the positive electricity flows is said to be at the higher
potential.
The measure of potential usually adopted can be best made clear by
the aid of another analogy. Potential of electricity is like the level of
water. The level of water is that which determines in what direction
water will flow when two vessels are put into communication, the surface
being at the higher level in the one from which water flows. Now, it is
true that we have a foot-rule method of measuring difference of level.
But without the foot-rule we might have measured it in this way : When
a pound of water is raised from a lower to a higher level' the attraction
of the earth is overcome through a certain distance and work is done,
the measure of the work being the product of the force overcome and
the distance, so that for different differences of level the work done is
proportional to the difference of level. Thus, if we had an instrument
for measuring the work we could in this way measure the difference of
level.
Now, electricity is an invisible thing, not material,—at least, in the
ordinary sense of matter; so that we cannot apply anything like a " foot-
rule " method to measuring differences of potential; but we can apply
the work method, and then we give the following definition : The measure
of the difference of potential of two charged bodies is the work that
would have to be done in carrying a unit quantity of positive elec-
tricity from the one of lower to that of higher potential.
To understand this definition clearly, there are several things to
notice about it. In the first place, it implies a unit of difference of poten-
tial, namely, unit difference of potential is the difference of potential
that exists between two charged bodies when unit of work is required to
carry unit of positive electricity from one to the other. In the second
place, it will be noticed that we have spoken only of differences of poten-
tial. In fact, this is all we have to deal with, just as it is only with
difference of water-level that Ave have to do, though'some standard level
or starting-point for the measurement of level may be most convenient.
In the case of water, the starting-point usually taken is the level of the
sea. Similarly, the most convenient practical starting-point in measur-
ino- differences of potential is that of the earth or anything in electrical
A-16
DUFF.
communication with it. Hence, the practical zero of potential is that of
the earth. But there is a theoretical or absolute zero of potential em-
ployed in the mathematical treatment of electricity, namely, the poten-
tial at an infinite distance away from a charged body. This absolute
zero, however, need not be employed in this work, just as the practical
zero of temperature—that of melting ice—suffices for all practical pur-
poses, though an absolute one is employed in theory,being about 273° C.
below zero. Further, it will be noticed that the above definition applies,
no matter what unit of electricity is employed. Now, some slight con-
fusion and difficulty are caused in electricity by the fact that two
different units are at different times employed. One we have explained
(§ 22) ; the other, and more important one, we will explain later.
Finally, though the above definition applies only to the difference
of potential between two charged bodies, it need not be limited to two
charged bodies, but may be made to apply equally to two points. It is
evident that if two points are in the neighborhood of charges,—i.e., are
in an electrical field (§ 23;,—work will be needed to carry electricity
from one to the -other, and they will therefore be at different poten-
tials. Hence we shall often have to speak of the differences of potential
between points.
25. Capacity.—If we put an insulated conductor close to the discharg-
ing knob of an electrical machine supplying, say, positive electricity, the
knob will, for a time, discharge positive electricity to the conductor, but
will soon cease to do so. But if we now bring
r> a the conductor equally near to another machine
giving electricity at a higher potential, a further
/"* charge will be imparted to the conductor. In
/ fact, with a source of electricity at a given
/ potential there is a certain maximum charge
Earth,/ that can be given to a conductor, for no more
Fig. 7. can be imparted when the charge on the con-
ductor has risen to the potential of the source.
How much electricity is required to raise the charge on a conductor to a
given potential depends on the capacity of the conductor. The capacity
of conductors corresponds to the breadth of jars containing liquids,
for it is the breadth that determines the amount of liquid requisite
to fill a jar to a given level. Hence we define the capacity of a con-
ductor as the quantity of electricity requisite to increase its potential
by unity.
26. Condensers.—A condenser is simply a means employed to
increase the capacity of a conductor, i.e., a means of getting a larger
charge on the conductor, the potential of the source being unchanged.
If the conductor mentioned in the last paragraph be a circular disc of
metal, A, and if a second similar one, B, connected with the earth, be
brought near the first, but not so as to touch it, it is found that the
ELECTRO-PHYSICS.
A-17
first one will receive a much greater charge than previously from a
source at the same potential. This combination of two plates with an
insulator (in this case air) between them forms a plate-condenser (Fig. 7).
The effect of the second plate, B, can be explained thus : The poten-
tial of A being raised, A tends to raise the potential of B; but B
remains at the potential of the earth, since it is connected with it by a
conductor. Hence, negative electricity must flow to B from the earth;
so that the negative potential so caused may just neutralize the positive
potential that A would cause, and would leave B at zero potential.
The negative potential thus produced by B's negative charge then reacts
on A, tending to lower its potential, but its potential does not fall, being
the same as that of the terminal of the machine. Hence, more elec-
tricity must flow to A from the machine to keep its potential up. Thus
the effect of the second plate is to enable A to receive a larger charge,
i.e., to increase its capacity.
27. Dielectrics and Inductive Capacity.—The above interaction be-
tween A and B is, of course, only possible when the medium between A and
B is non-conducting. A non-conducting or insulating medium between two
electrified conductors is called a dielectric. In the above case it was air,
but it might have been glass, ebonite, or any other insulator whatsoever.
We should find, however, a difference between different dielectrics. For
equal thicknesses of the dielectric, glass as a dielectric would give a con-
denser of three times the capacity that air would, and solid paraffin two
times. This quality of an insulator that determines the capacity of a
condenser in which it is employed as dielectric is called its inductive
capacity.
To be more precise, we must assign a method of measuring the
property called inductive capacity. It can be done in this way : Deter-
mine the capacity of a condenser in two sets of circumstances,—first, with
air as its dielectric ; second, with, say, glass as its dielectric. Divide the
capacity of the condenser in the latter case by its capacity in the former,
and the ratio is called the specific inductive capacity of the glass. The
ratio so determined will be found to be the same, no matter what shape
or size of condenser is employed. It depends only upon the dielectric.
Hence, the specific inductive capacity of a dielectric is the ratio of the
capacity of a condenser with that substance as dielectric to that of
another exactly similar but with air as dielectric.
Note.__The reader must be careful not to confuse the terms capacity of a condenser
(§ 25) and inductive capacity of a didectrk.
28. Forms of Condensers.—It.is evident from § 26 that, if the
thickness of the dielectric of a condenser be decreased, the inductive
effects will be increased, and so the capacity of the condenser increased.
Again, it is evident that increasing the area of the plates will also
increase the capacity of the condenser. Hence, on the whole, the capacity
of a condenser is proportional (1) directly to the area of the plates; (2)
2
A-18
DUFF.
inversely to the thickness of the dielectric; (3) directly to the specific
inductive capacity of the dielectric.
Condensers are made in many forms. The usual dielectric is glass,
for its specific inductive capacity is particularly high. The jar form of
condenser is the most common and most convenient. It is simply a
glass jar coated with tin-foil two-thirds of the way up, inside and outside,
and closed with a cork, through which a metal rod passes carrying a knob
at the upper end, and connected at its lower end with the internal coat-
ing. To charge it, the knob is connected with a machine and the outer
coating with the earth. It will thus charge to the potential of the
machine; but if the latter be too high, the glass is apt to be broken by a
disruptive discharge through it. Such condensers are used in connection
with the terminals of machines to enable
them to store up larger quantities of elec-
tricity, and thus cause a larger discharge.
(Vide also section on "Franklinic Elec-
tricity.")
29. Seat of Charge and Residual
Charges.—At the end of this section we
shall make a short attempt to explain what
electricity is, and so we state here a few
facts as to the action of Lej'den jars that
bear on that point. If a jar be made with
stiff, removable coatings and charged, it will
be found, on removing the coatings, that no
charge really resides on them; and yet, on
restoring them and discharging the jar, the
fig. 8. original charge will be reproduced. Such,
however, will not be the case if the glass of
the jar be thoroughly discharged by passing it through a flame while
the jar is apart. Hence the charge, whatever its nature, really resides
in the dielectric.
Again, after an apparently complete discharge of a jar a residual
charge is slowly developed, as may be seen by again discharging it,
whereupon a small discharge will be obtained. This has been described
as a " soaking " of the electricity " into " the dielectric, and a subsequent
" soaking out." Its real nature will be discussed later.
Again, every charge has its corresponding residual charge and dis-
charge ; so that if several charges be given to a jar, the charges being
either of the same or of different kinds, all the residual charges can be
obtained, but in the opposite order to the order of the original charges.
This is an exact parallel to certain phenomena obtained by twisting an
elastic rod. If such a rod be twisted, and then allowed to gently untwist,
it will not do so completel}r,but will retain a residual twist and will show
a residual untwisting. Moreover, if the rod be given several such twists,
ELECTRO-PHYSICS.
A-19
whether in the same or in opposite directions, corresponding residual
twists and untwistings also take place in the opposite to the order of
the original twists.
Now, these latter are due to elasticity in the rod ; and the similar
action of the Leyden jar, taken together with what was stated as to the
seat of the charge, suggests that electrification is an elastic phenomenon
of the dielectric, or of something associated with it. Of this, later.
Magnetism.
30. We turn now to certain other phenomena long thought quite dis-
tinct from the preceding, but which fundamentally are closely allied. We
shall take them up from the point of view of this connection. If a
copper wire be bent into a spiral around a glass tube coArering a steel
rod, such as a knitting-needle, and a charge of electricity—say, from a
Leyden jar—be passed through the spiral, the steel rod will be found to
Fig. 9.
have acquired certain new properties. These properties are called
magnetism, and the rod is called a magnet. The properties are these :—
(a) If freely suspended in a horizontal plane, the magnetized needle will take up a
definite nearly north and south direction, to which it will return after being disturbed.
The end pointing nearly north is called the north-seeking pole of the magnet, the other the
south-seeking pole.
(6) If two such needles be suspended near each other, it will be found that like poles
repel each other and unlike poles attract each other.
But these two properties are not distinct. The first to show this
was Gilbert, of Colchester (" the Galileo of Magnetism "), who lived in
the sixteenth century. For the earth itself is a magnet, and consequently
acts on other magnets according to (b). The magnetic action of the
earth can be fairly well represented by imagining a great magnet, about
half the earth's diameter in length, buried, with one end below Boothia
Felix, in the north of Canada, and the other at the opposite point in the
southern hemisphere. It will now be seen that if we call that pole of
this great earth-magnet which lies in the northern hemisphere the mag-
netic north pole of the earth, we should properly call the north-seeking
pole of a magnetic needle a true south pole, and the south-seeking pole
a true north pole. But custom is quite inconsistent in this matter; so
we shall have to adhere to the terms north pole and south pole of a
magnet, meaning thereby north-seeking and south-seeking, respectively.
31. Magnetic Induction, Temporary and Permanent.—Supposing
that in the preceding way a magnet has been produced, we can from that
mao-net make others, as follows: Take another unmagnetized steel
A-20
DUFF.
needle and stroke it from end to end, always in the same direction, with
the north pole of the magnet. It will be found that the unmagnetized
needle has become magnetized with a south pole at the end which the
north pole of the magnetizing needle last touched. In this way any
number of permanent magnets can be made by induction.
But temporary magnetism can also be induced. Of this we have an
example in the familiar experiment of shoving a pole of a magnet among
soft-iron filings, whereupon the filings cling to the pole. This is simply
due to the fact that the iron particles become, for the time being, magnets
attracted by the inducing pole and attracting each other; but immedi-
ately the inducing magnet is removed they cease to attract one another;
their magnetism is gone. This merely temporary induction of magnetism
in soft iron is of great importance. It will be noticed that the difference
is that hard iron or steel is susceptible of permanent magnetism, soft
iron of merely temporary magnetism.
The oldest known example of induction is the inductive action of
the earth's magnetism on a certain compound of iron called magnetic
iron-oxide, giving rise to the lodestone, which is supposed to have been
named magnet from being found in Magnesia, in Asia Minor. Being
itself a magnet, it can be used to magnetize a needle, and in this way
the first mariners' compass was produced. There seems little doubt
that the Chinese knew and used this property four thousand years ago
(see Sir Wm. Thomson's " Popular Lectures," vol. iii, " Navigation").
32. Unit Magnetic Pole ; Laws of Magnetic Attractions and
Repulsions ; Magnetic Field.—The definition of unit pole is like that
of unit charge of electricity, viz., unit magnetic pole is that which at unit
distance from an equal similar pole repels it with unit force. Having
thus defined unit pole, the laws of magnetic attractions and repulsions
may be stated thus :—
(a) Like poles repel one another, unlike attract.
(6) The attractions and repulsions are proportional to the strength of the poles.
(c) The attractions and repulsions are inversely proportional to the square of the
distance between the poles.
These are the same as for quantities of electricity, and need not be
enlarged on.
A magnetic field is the portion of space in the neighborhood of mag-
netized bodies considered with reference to magnetic phenomena. The
strength of the field at any point is the force with which the field would
act on a positive unit pole at that point. A line of magnetic force is a
line whose direction at every point is that of the direction of the mag-
netic force. Magnetic potential will probably not be referred to in the
sequel; so all that need be said of it is that it is measured like electrical
potential (§ 24).
33. Astatic Combination of Magnetic Needles.—Any freely-sus-
pended needle is subject to the directive force of the earth. If a quite
ELECTRO-PHYSICS.
A-21
similar needle be attached to it so that similar poles point in opposite
directions, and the combination be freely suspended, the needles will,
under the earth's influence, tend to turn in opposite directions ; and if the
needles be perfectly similar and of equal strength, the earth will exercise
no directive force on the combination,—or, it will be astatic. But as it is
practically impossible to get a perfectly similar pair of needles, we must
content ourselves with a nearly astatic combination ; that is, a combina-
tion on which the earth exercises but a very feeble directive force. Such
a combination is useful for purposes that will be stated later.
34. Facts Bearing on the Nature of Magnetism—Molecular
Theory.—If a magnet—say, a magnetized piece of watch-spring—be cut
in two, it will be found that each piece is a magnet with two opposite
poles. The same holds true no matter hew often we may cut a magnet
up or how small particles we may reduce it to.
Hence, magnetism is a property of the ultimate
particles of a substance.
In an unmagnetized needle these little mo-
lecular magnets lie higgledy-piggledy,—in all direc-
tions,—and magnetization consists in turning them
so as to face in the same direction. When a piece
of iron is fully magnetized or saturated,—i.e., has
received the full measure of magnetism it can
contain,—all these molecular magnets have faced
in the same direction; when magnetized below
saturation, some have wheeled around and some
have not, or all have wheeled around, but not the whole way. Thus,
in the body of a magnet, each north pole will be neutralized by an
adjacent south pole belonging to a neighboring molecule. The un-
neutralized north poles at one end give a north pole to that end of the
bar, and the unneutralized south poles at the other end a south pole there.
This is the molecular theory of magnetism.
Some facts bearing on it may be mentioned. It is evident that on
this hypothesis magnetization should be facilitated .by anything that
tends to set the molecules in motion ; and on the other hand, after the
magnetizing agent has ceased to act, demagnetization should be accel-
erated by the same means. This is found to be so. Hammering, twist-
ing, and bending tend to set the molecules free, and thus aid magnetiza-
tion or demagnetization, as the case may be. Moreover, heating, which
consists in giving more vigor to the molecular motions (§ 10), also assists
in a similar way.
Again, if such a wheeling into line actually takes place, we might
expect to find a change in the length of a bar on being magnetized.
This is a well-marked phenomenon amounting in certain cases to ^Woou
of the whole length of the bar.
Finally, strong support is given to the theory by the action of a
A-22
DUFF.
model, consisting of a large number of small magnetic needles, constructed
recently by Ewing. This would not be the place to go into details.
Suffice it to say that the most of the peculiar stages of magnetization and
demagnetization of a bar are imitated by his molecular model.
Kinetic (or Voltaic) Electricity.
35. Currents of Electricity.—We proceed now to consider the
properties of streams or currents of electricity. But it will be under-
stood that the electricity we have to do with differs in no way in kind
from that which we have already treated of, though it does differ at first
sight as regards method of production, and certainly differs greatly in
potential and quantity. Static electricity as produced by the machines
referred to in § 20 is electricity at very high potential, but very small
in quantity. The electricity we get by the contrivance described below
is electricity at very low potential, but in large quantities. Or, if we
compare the stream of electricity between the knobs of a statical elec-
trical machine and the current of electricity produced by a voltaic pile,
the difference between them is like that between a lofty water-fall down
which a small stream falls and a broad, slow river of small pitch. In
both of the latter cases it is water, and so too in both of the former cases
it is electricity.
Volta's cell for procuring a current of low-potential electricity is
this : Take a zinc and a copper plate, connect them by a wire and dip them
into water containing a small proportion of sulphuric acid. Immediately
bubbles will begin to be given off from the copper plate. Moreover, a
new property has been conferred on the wire ; for if it be wound in a
spiral around a glass tube containing a piece of soft-iron wire, it will be
found to make the latter temporarily a magnet; hence a current of
electricity is passing along the wire. But this method of showing the
presence of a current is one far from satisfactory or handy ; so we must
proceed to explain a much better one.
36. Indicator of Current ; Oersted's Principle ; Galvanometer.
—The following .connection between a current of electricity and a
magnet discovered by Oersted goes by the name of Oersted's principle,
viz., a freely-suspended needle in general is deflected by the passage of
a current of electricity in its neighborhood. This may be readily tested
by an electrical machine and a freely-swinging needle. On sending posi-
tive electricity from south to north over the needle it will be found to
deflect with its north end west, and reversing the direction of the cur-
rent, or changing from above to below, will reverse the direction of the
deflection. The direction of the deflection will always be given by the
following rule : Suppose yourself swimming in the current and facing the
needle, then the north pole will be deflected to your left hand. This is
Ampere's rule. A simpler one is : Place }-our right hand on the current
with the palm toward the needle, then the north pole of the magnet will
be deflected in the direction of your thumb.
ELECTRO-PHYSICS.
A-23
&
3D
A sensitive needle will thus serve to detect a current of electricity.
But we can greatly increase the sensitiveness of the test as follows:
Instead of using a single straight portion of the wire, let us
make a circular coil of part of it and put the needle at the
centre of the coil, and in its plane. Then each part of the
current will act on the needle, and, since the current cir-
culates several times around the needle, the effect will be
correspondingly multiplied. Such a contrivance was
originally called a multiplier, but it is identical in prin-
ciple with the present-day galvanometer.
To render small deflections of the needle visible several
devices have been employed. Sometimes a long, light
pointer (say, of aluminium) is attached to the needle. The
motion of the end of the pointer is greater in proportion
to its length than that of the needle, and so small deflections are made
more evident.
A much more effective device, due to Pog-
gendorff, is to attach a very light mirror to the
N—I—S needle and allow light to fall on the mirror and
then be reflected to a somewhat distant scale.
It is a simple matter of geometr}' to show that
the direction of the reflected ray is turned b}r
the motion of the mirror through twice as great
an angle as the mirror is turned through by the
passage of the current. This is what is known
fig. 12. as Thomson's reflecting galvanometer.
Another means of making the galvanometer
a more sensitive detector is to use an
astatic combination of needles (§ 33),
letting the current circulate around one
of the needles onby. Thus, the earth's
directive force being greatly reduced
by the pitting of one magnet against /" f I ^
the other while the directive force of
the current is undiminished, since it
acts on one needle only, the astatic pair
will answer much more sensitively to
the passage of a current. This gives
us the astatic galvanometer. Or, a single
needle may be used and the earth's di-
rective force counteracted by a large, Fig. 13.
stationary, compensating magnet, M,
producing a field in the opposite direction to the earth's field. By this
device the mirror can be turned so as to reflect in any desired direction.
Such means as these give very sensitive instruments for detecting the
presence of currents.
4-
O
A-24
DUFF.
37. Volta's Cell.—If the plates of Yolta's cell, described in § 35, be
connected with the ends of the galvanometer coil, an immediate deflection
of the magnet announces the passage of a current of electricity. If
instead of a galvanometer a simple needle be used, a straight portion of
the circuit carrying the current being held over it, it will readily be seen,
from the direction of the deflection of the needle, taken along with the
Fig. 14.
rules given in § 36, that the positive current goes from the copper plate
along the wire to the zinc plate, and thence from the zinc plate in the
liquid to the copper plate. (As a memoria technica, the rule zinc in
liquid to copper may be shortened to z-in-c,—spelling the word zinc.)
Terminal wires or binding-screws are usually attached to the plates.
Now, considering the external part of the circuit (i.e., the part out of the
liquid), the positive electricity passes from the terminal
of the copper plate to that of the zinc. Hence the
copper terminal is called the positive pole and the zinc
terminal the negative pole. Considering now the part
of the circuit in the liquid, the current passes from the
zinc plate to the copper plate. Hence the zinc is called
the positive plate and the copper the negative plate.
If this be kept in mind, no confusion need be caused
by the paradox that the positive pole is the terminal
of the negative plate and the negative pole the terminal
of the positive plate.
The evolution of gas at the copper plate shows
that some chemical reactions are going on in the cell.
What is really taking place is, that the sulphuric acid
is acting on the zinc, thus :—
Zn + H2S04=ZnS04-f-H2
So that hydrogen is set free, and this is the gas that
is appearing at the copper plate. The zinc sulphate that is formed
remains in the liquid, while the zinc is gradually eaten away. This is
the simplest possible form of voltaic cell.
38. Magnetic Field of Force of a Current.__Wherever a mao-net
is subject to magnetic force there is, by § 32, a field of magnetic
force. Hence a current has a magnetic field. It is a comparatively
simple problem to determine the direction of the lines of force of this
Fig. 15.
ELECTRO-PHYSICS.
A-25
field, i.e., the direction of the force at any point in the field. A magnet
tends everywhere to set itself at right angles to the current, no matter
on which side of the current it is. Hence, the lines of force are circles
surrounding the current with their centres on the current. They may
bethought of in this way : Imagine the current surrounded by circular
cylinders, the current occupying the axis. Then the lines of force are
circles, got by taking sections of the cylinder at right angles to the axis.
The direction of the force along these lines of force relatively to the
direction of the current may be found by Ampere's rule (§ 36), or
it is more simply remembered from the rule that the direction of the
current is related to the positive direction of the lines of force, as the
thrust to the twist in a right-handed screw.
39. Electro-magnetic Units of Current and Quantity.—We have
already stated the action of a current on a magnetic needle. Suppose,
now, we take a wire in which a current is flowing and bend it into a
circle. Let the circle be one of unit radius. Think, now, of a part of
this current of unit length. It will exercise a certain force on a unit
magnetic pole at the centre of the circle. What force it will so exercise
will depend on the strength of the current. The unit of current that we
adopt is the current which, under the above circumstances, will exert
unit force on the unit magnet-pole at its centre. Or, to sum up the
definition, the electro-magnetic unit of current is a current unit length
of which bent into an arc of a circle of unit radius exerts unit force
on a unit magnetic pole placed at the centre. If the C. G. S. units
(8 11) be employed, this is called the absolute electro-magnetic unit of
current. In practice, however, a current equal one-tenth of the absolute
unit of current is employed as unit, and is called the ampere. The
electro-magnetic unit of quantity is the quantity that is conveyed by
unit current in unit time. The practical unit of quantity is only one-
tenth of the absolute unit, and is called the coulomb.
40. Electro motive Force.—When matter is set in motion or has
its motion kept up in spite of resistance, we say the effect is due to a
force. When a current of electricity is started or kept up in spite of
resistance, we refer this effect to a force moving the electricity, or an
electro-motive force. Hence, we define electro-motive force as whatever
sets up or keeps up a current of electricity.
The usual cause of a flow of electricity is a difference of potential.
(For a careful account of what is meant by differences of potential see
§ 24.) Hence, potential difference is the usual electro-motive force;
but it is not the only form. Just as in the case of water the usual cause
of flow is a difference of level—but flow may be produced by other
causes, such as a force-pump,—so also, in the case of electricity, other
forms of electro-motive force than potential difference are knoWn.
Now, we can readily define unit difference of potential, and we shall
take the same as our definition of unit electro-motive force generally.
A-26
DUFF.
There is no inconsistency in this,—although electro-motive force is not
always due to difference of potential,—just as there is no inconsistency in
describing the pressure produced by a force-pump in a water-pipe as
equivalent to a " head " of so many feet, although there may be no actual
difference of level.
Hence, we shall take the unit of electro-motive force as simply the
same as the unit difference of potential. The reader is therefore
recommended to carefully master § 24, dealing with potential. Then,
adopting the electro-magnetic unit of quantity, we define as follows :
Unit difference of potential or unit electro-motive force exists' between
two points when it requires the expenditure of unit of work to bring a
positive unit of electricity from one point to the other against the
electro-motive force.
This absolute unit would be far too small. Hence the practical unit,
called the volt, is taken as equal to one hundred million (100,000,000)
absolute units. Although the electro-motive force of Volta's simple
cell (§ 35) is not always quite the same, yet, roughly speaking, it is about
a volt.
41. Resistance.—If we take the Volta cell, described on page 22,
and pass the current produced by it through wires of various lengths,
thicknesses, and materials, including a galvanometer in the circuit, we shall
find that the current produced varies with all three of these conditions,
viz., that the current is weaker the longer the wire, is also weaker the
thinner the wire, and is weaker for some materials than others, even with
the same size of wire. For the same length and thickness, it will be
found that the current through copper wire is greater than that through
an iron or a platinum one. Hence we say that iron and platinum offer a
greater resistance to the current than copper does, and that long or thin
wires of any material offer greater resistance than short or thick wires
of the same material.
To keep this matter clear, we may remember the analogy of water
passing through pipes. The longer the pipe, the greater the frictional
resistance, and, the narrower the pipe, the greater the frictional resist-
ance. Finally, with pipes of the same size, the resistance will depend
somewhat on the material of the pipe. We conceive electrical resistance
to be somewhat of the nature of frictional opposition to the current.
The greater the resistance of a conductor, the smaller the current
that a given electro-motive force can force through it. Hence wre define
the unit of resistance in terms of the units of electro-motive force and
current, and we say that a conductor has unit of resistance when unit
difference of potential between its ends causes unit current to flow
through it. If we use the absolute units of current and potential differ-
ence (or electro-motive force) this definition, of course, gives us the
absolute unit of resistance. The practical unit is much larger, containing
1,000,000,000 absolute units, and is called the ohm. It is the resistance
ELECTRO-PHYSICS.
A-27
of a column of mercury 1 millimetre square and 106^ centimetres long.
For convenience we tabulate these three important practical units
thus :—
Unit of called the roughly is that of and contains — abso-lute (C. G. S.) units
Current ampere one-tenth
Electro-motive force volt a simple Volta cell a hundred million
Resistance ohm a column of mercury 1 mm. 6quare and 1 metre long a billion
42. Defects of the Simple Cell of Volta.—The requirements of a
good Yoltaic cell are so numerous that all can hardly be satisfied at once.
The electro-motive force should be high and constant. Neither part of
this condition is well fulfilled by Volta's simple zinc-copper cell. Its
electro-motive force is not high as cells go, and not at all constant. The
chief cause of its falling off in electro-motive force is what is called
polarization, i.e., a change in the surface of the plate produced by the
deposition of the products of the decomposition in the cell; in this case
the substance deposited is hydrogen-gas on the copper plate, by which the
surface of the plate is altered ; so that we have really a different plate to
deal with.
The other chief defect of the simple Yoltaic cell is excessive local
action, as it is called. By this is meant a local and useless consumption
of the plates apart from the consumption necessary to produce the elec-
tric current. In the present case it takes the form of a gradual consump-
tion of the zinc plate owing to impurities or irregularities in the plate.
Wherever in the zinc a foreign particle (say, of iron) is exposed, there we
have a little local battery formed by that particle, the fluid, and the adjacent
parts of the zinc itself, and thus the zinc is consumed without this con-
sumption adding to the main current. The same effect is produced by
mere irregularities and inequalities in the zinc itself, for two parts of the
zinc plate with slightly different physical qualities (e.g., hardness) will
act as separate metals, again giving rise to local action.
Local action may be got rid of by " amalgamating " the zinc plate,
as it is called, i.e., bv giving it a surface-covering of an amalgam of zinc
and mercury.' This is done by first cleaning the plate with dilute
sulphuric acid and then rubbing mercury over it. If the plate is one of
smooth-rolled zinc it will at once take on a bright coating of zinc amalgam.
The zinc consumed in the production of the current is removed from the
amalgam and its place taken by fresh zinc from the plate below the coat-
"The action is thus rendered uniform over the surface of the plate,
ing
an
d any foreign particles in the zinc are brought to the surface of the
A-28 DUFF.
amalgam and carried away by the hydrogen bubbles. In the use of bat-
teries containing zinc plates care must be taken to see that the zinc is
kept properly amalgamated. If a battery is used daily new zinc may
need to be amalgamated daily for four or five days, but after that once a
week or fortnight will suffice.
To describe the remedies for polarization we would have to describe
the various modifications of Volta's cell now employed. For this the
reader is referred to the separate section on " Voltaic Electricity."
43. Controversy as to the Action of the Voltaic Cell.—Nearly
ever since the invention of the voltaic cell a spirited warfare has been
waged between two schools of physicists,—viz., the " contact" and the
" chemical" schools,—as to the method of action of the cell. As in all
such cases where the opponents are honest in the positions assumed, the
truth probably lies between the two extremes. To make the matter plain,
however, we shall state the extreme positions.
The older or contact theory is this : (1) on joining two metals, either
directly or by a wire, a difference of potential is observed ; (2) when the
metals still joined are immersed in a liquid which acts upon one more
than the other, the chemical action equalizes the potentials, and in so
doing causes a flow of electricity along the connecting wire; (3) the mo-
ment the equalization of potential has commenced the difference is re-
newed again at the point or points of contact between the metals, and so,
if no disturbing cause interfere, a continuous flow of electricity is kept
up until the metal most acted on is entirely dissolved. (Gordon.)
Here, it will be noticed, the primary point emphasized is the differ-
ence of potential produced by the mere contact; but it is not claimed
these differences alone will produce a current. A current will only be
produced when some extraneous means—e.g., chemical actions—are em-
ployed to keep up the difference. If the mere contacts without chemi-
cal reaction could produce a current there would be a constant supply of
fresh energy with no corresponding disappearance of energy from else-
where, and a consequent violation of the law of conservation of energ}-.
Now, in a circuit consisting only of metals, all at the same temperature,
no chemical actions will be observed. Hence, according to the law of
the conservation of energy no continuous currents can be produced,__
i.e., there can be no resultant electro-motive force. To put it in the
concrete : Suppose we have a circuit of three metals, a, b, c,__ A ,__
and suppose we call the electro-motive forces at the contact, respectively
F»b,Ebc, Fea, reckoning them all in the same direction, then, since there is
no current,
Fab + Fbc + Fca = 0;
and the same will be true, no matter how many different metals may be
included in the circuit.
We can put the above in another way ; in fact, the way in which it
ELECTRO-PHYSICS. A-29
was originally put by Volta himself. Of course, the electro-motive force
from a to c is equal, but of opposite sign to that from c to a; or,
Fac =—Fca. Hence, from the above equation,
Fab+Fbc = -Fca
= F •
or, we get the same electro-motive force from a and c directly on contact
as when we insert any other or, in fact, any number of other metals
between them. This bearing of the conservation of energy on the
question was not considered by Volta's followers, and so they were led
into statements which caused Faraday to altogether deny the existence
of contact electro-motive forces, and to refer the whole thing to the
chemical actions.
The position assumed by the chemical theory, with which Faraday's
name is associated, is this: (1) when two plates are placed in the liquid,
but not in contact, they are brought to different potentials ; (2) if they
be then connected by a wire, electricity rushes along the wire to equalize
the potential of the plates ; (3) and since this difference of potential is
constantly renewed, there will be a constant flow of electricity till the
plate most acted on is consumed.
Those who maintain the chemical theory also do so now in a modi-
fied form. While maintaining that the chief seat of electro-motive force
is the Zn-liquid junction, they admit a real, though they claim compara-
tively slight, potential difference at the metal contacts. The real exist-
ence of this potential difference at metal contacts has been shown by
Thomson, and is evident from the facts of thermo-electricity.
The advocates of the contact theory do not attempt to explain the
cause of the contact forces. The advocates of the chemical theory ad-
vance a reasonable explanation of the potential differences produced at
the zinc-acid junction. It is this : The liquid in contact with the plates
contains atoms, some charged positively, some negatively,—sa}r, oxygen,
ever}r atom of which has a certain negative charge; and hydrogen, every
atom of which has a positive charge. Both the Zn and the Cu plates
attract oxygen, as is shown by their readiness to rust or oxidize. But
the zinc attracts oxygen more strongly than does the copper. Now, in
the liquid there are, at a certain moment, a goodly number of free
atoms (§ 6), for some of the molecules are always breaking up and
immediately recombining, with an interchange of atomic partners. The
distance at which zinc will exert any appreciable attraction on an oxygen
atom is very small,—say, one-ten-millionth of a millimetre,—and this is
called the molecular range. The Zn plate, then, acts on all momentarily
free atoms of oxygen within molecular range of it, attracting them to
itself. But their place in the thin sheet of liquid near the plate, whose
thickness is the molecular range, will then be immediately taken by other
free atoms coming in by diffusion from more distant laj^ers, and thus the
A-30 DUFF.
supply of oxygen atoms is kept up, and there will be a gradual pro-
cession of oxygen atoms through the liquid toward the zinc,—at a rate
determined by the electro-motive force acting and the rate of diffusion
natural to the liquid employed. Now, all the oxygen atoms that reach
the zinc, each with its negative charge, neutralize a certain portion of
the positive electricity of the zinc, and thus leave it charged negatively.
If no channel be afforded for the escape of this negative charge, it soon
becomes so large as to repel the similarly-charged oxygen atoms with as
great a force as the zinc naturally attracts them, and then the process
ceases.
44. Ohm's Law.—The basis of exact measurements in electricity is
a famous law published by Dr. G. S. Ohm in 1827,—a law that has stood
the test of numerous keen examinations since, and now deserves to rank
with the laws of gravitation and of electro-static attractions and repul-
sions as a real law of nature.
Ohm's law is that the current produced in a conductor by an electro-
motive force is proportional directly to the electro-motive force and
inversely to the resistance of the conductor; or, C is proportional to E
divided by R, which is written in mathematics thus :—
CaR
Such a proportion is equivalent to an equation into which a constant
numerical factor (k) enters; thus,
R
What this constant factor k is will depend on what units we employ.
Now, by referring back to § 41, it will be seen that by our defini-
tion of the practical unit, R is unity when C and E are unity, or 1 = k \ ;
hence k is one and may be omitted; thus,
Our system of units was, in fact, chosen with a view to having this so.
46. Ohm's Law and Resistance.—The idea of electrical resistance
is frictional opposition to the flow of electricity, just as ordinary friction
between two bodies means opposition to the movement of one over the
other. Now, we may write Ohm's law thus :—
So that resistance is the ratio of electro-motive force to current pro-
duced. The real meaning of Ohm's law is that this ratio is, for a given
conductor in a given physical condition, a constant; so that our measure
of the resistance of a conductor is the constant ratio of the electro-
motive force producing a current in it to the current so produced.
ELECTRO-PHYSICS.
A-31
The resistance of a conductor depends on the dimensions of the
conductor, as follows: If the length of the conductor be 1, the area of
its cross-section a, then its resistance is
R = k -,
a
where k is a constant independent of the dimensions of the wire. If we
take a piece of the conductor of unit length and unit cross-section, 1= 1
and a = 1, and then R = k ; or, k is the resistance of a piece of the con-
ductor of unit length and unit cross-sectional area, and is called the
specific resistance of the substance of which the conductor consists.
Conductivity.—The conductivity, or conducting power of a conductor,
will be greater, of course, the less its resistance. We may, then, take it as
the reciprocal of the resistance, or = i, and then from Ohm's law it will
mean the ratio of the current in the conductor to the electro-motive
force that produces it.
46. Conditions on which Resistance Depends.— The Material of
the Conductor.—Some substances are naturally good conductors, and
others naturally poor. Among metals, copper is one of the best conduc-
tors, and hence it is the most commonly employed. The conductivity
of silver stands higher than that of copper, but its cost prevents its use.
After copper come platinum, iron, lead, mercur}', German silver, in the
order named. It is interesting to note that this is also the order of the
metals as regards conducting power for heat. In fact, the ratio of the
conductivities for heat and electricity is nearly constant not only for
metals, but also for allo3'S.
Physical State.—In all ordinary metal conductors the conductivity
decreases as the temperature rises. The increase of specific resistance per
unit rise of temperature is called the temperature coefficient of the sub-
stance. It is nearly the same for all pure metals except thallium and iron,
being .0037647 per degree centigrade. Again, metals become worse con-
ductors on having their hardness increased. The resistance of steel is
increased by tempering, while hard-drawn copper wire is a worse con-
ductor than annealed copper. Finally the resistance of a wire is changed
by strain; stretching increases the resistance of the wire, while longi-
tudinal compression decreases its resistance.
47. Conduction of Liquids.—Liquids are divided into two classes:
(1) those which conduct without decomposition, as liquefied metals and
A-32
DUFF.
some compounds; (2) those which are decomposed by the passage of
the current, and are called electrolytes, the process of their decom-
position being called electrolysis. We shall take electrolysis up more
fully a little later. But we anticipate enough to say that Ohm's law
holds for electrolytes also (§ 62).
48. Resistance of a Multiple Arc.—A multiple arc is the technical
name applied to an arrangement of wires in which several wires connect
two points so that several channels are open to the flow of electricity.
(Fig. 16.) We are supposed to know the separate resistances,—say,
RM R2, R3,—and we wish to know what the effective resistance of the
combination will be. If the potential at A and Z be Vx and V2, then the
difference, Vx — V2, will be the electro-motive force, E,acting along each
wire; and then, by Ohm's law,
E _ E , n E
Ci=R1'.C» = Ri'andC,8=R,
Suppose these wires removed and replaced by a single wire of resistance,
R, such that the current still remains the same, or C = Cj + C2 -f- C3 ;
then, since Ohm's law would still hold for this conductor,
t—R
1111
Hence'R=R1+R2 + R3
This means that the conductivity of the combination (or the reduced
conductivity of the multiple arc) is simply the sum of the conductivities
of the separate conductors, and R can be readily calculated.
As a simple example, let us find the resistance of a wire that would
just replace three in multiple arc, whose resistances are 1, 2, and 3 ohms,
respectively:—
1111 6 + 3 + 2 11 6
R=I+2+3=---6---= "6"*- R=ITohra-
49. Arrangement of a Number of Cells for Greatest Current.—
For the purpose of what follows, we shall employ the simple conven-
tional sign,
to represent a cell, the large line representing the zinc, or positive plate,
and the small one the copper, or negative plate, so that the current flows
in the direction of the arrow. We must also define the terms external
and internal resistance. That part of the resistance of a circuit which is
constituted by the cells used is called the internal resistance, and the
remainder, due to the parts of the circuit outside the cells, is called the
external resistance.
ELECTRO-PHYSICS.
A-33
There are two separate ways in which we can arrange a battery of
cells, and a third way that is a combination of the two.
(a) In series, i.e., the copper of each being connected to the zinc of
the next, thus :—
^-\^-\-\
Fig. 17.
(b) Abreast or in multiple, i.e., all the coppers being joined together
and all the zincs together, thus :—
T
T
Fig. 18.
Comparison of the Two.—Let the electro-motive force of each cell
be E. Then it is easily seen that in the arrangement in series the second
zinc plate is at the same potential as the first copper plate, and therefore
E in potential below the first zinc plate. The second copper plate is,
therefore, 2E below the first zinc plate. The last copper plate is nE in
potential below the first zinc plate ; hence the electro-motive force of
the combination is nE. But if the resistance of each cell be R, then the
resistance of the combination is nR. If, then, the internal resistance be
much larger than the external, the whole resistance of the circuit will be
n times what it would have been with only a single cell, while the electro-
motive force will have been increased n times also ; so that the" n cells
will not give a much better current than one cell.
If, on the other hand, the external resistance be very large compared
with that of a single cell, the arrangement in series will be advantageous,
since it greatly increases the electro-motive force in the circuit without
adding appreciably to the total resistance.
Turning now to the arrangement abreast,—since all the positive
plates are at the same potential and all the negative plates at the same
potential, the electro-motive force of the whole arrangement is simply-
that of a single cell. But since n channels are now afforded for the flow
of the current through the battery part of the circuit, the resistance of
the combination will only be one nth that of a single cell, or R/n. If,
now, R be small compared with the external resistance, we shall not have
reduced the whole resistance of the circuit much by dividing R by n, and
so the arrangement will hardly be more effective than a single cell would
be. But if the internal be the chief portion of the resistance, then by
dividing it by n wre shall have greatly reduced the total resistance.
A-34
DUFF.
Hence, a general rule: If the resistance of a single cell is less than
the external resistance, arrange your cells in series; if greater, arrange
your cells abreast.
(c) But there is a third way of arranging the cells. Suppose, e.g.,
we have 24 cells, then we can divide them into six groups of four each.
Each group of four we can arrange in series so as to act as a single cell,
of an electro-motive force 4E and an internal resistance 4R. Then these
six groups can be arranged abreast, so that the electro-motive force is
still 4E, but the internal resistance of the combination ™; and then, if
the external resistance be r, by Ohm's law we shall have a current of
4E 24E
r+4R— 6r+4R
6
But we could also have divided this into eight groups of three cells
each, and then the current would have been
3E 24E
r + 3R "~ 8r + 3R
8
or four groups of six each, and which of these will give the greatest
current will again depend on the relative magnitude of r and R; and if
the matter is investigated mathematically, we shall arrive at the following
rule for the arrangement giving greatest current: Divide the cells into a
number of groups, such that the ratio of the number of groups to the
number in each group shall be as nearly as possible equal to the ratio of
the resistance of a single cell to the total external resistance. Then
arrange each group in series (a), and put all the groups abreast (6).
Wheatstone's Bridge Measurement.
50. Standards of Resistance and Electro-motive Force.—We
proceed now to indicate briefly the exact methods employed in measuring
resistance and electro-motive force. Before doing so, we must describe
the standards used in measuring resistance.
Resistance.—At a given temperature a given wire has a perfectly
definite electrical resistance. Accordingly, if we take a bobbin of wire
(German silver is usually employed), the coils being covered with silk or
some insulator, so that there is no " short-circuiting," or passage of cur-
rent from coil to coil in contact (the current must pass longitudinally
from end to end of the wire), we can use such a bobbin as a standard for
comparing electrical resistance ; and further, if we take a series of such,
graduated to ohms and parts of an ohm, in the same way as weights for a
fine balance are graduated in grammes and parts of a gramme, such a
series of graduated resistances will enable us by comparison to measure
any unknown resistance. Such a series, arranged with their terminals
ELECTRO-PHYSICS.
A-35
on the cover of a box, in which the bobbins hang for protection, is called
a resistance-box. The alloy German silver, which consists of nickel and
copper, is usually employed, because it has a low temperature coefficient,
i.e., suffers but small proportionate increase of resistance on increase of
temperature.
Electro-motive Force.—Any very constant cell can be employed for
comparing electro-motive forces. The one usually employed is a cell
invented bjr Latimer Clark, and having a very constant electro-motive
force. The poles are amalgamated zinc and mercury, and the liquids
are sulphate of zinc and a paste of sulphate of mercury. Its electro-
motive force is 1.457 V.
51. Wheatstone's Bridge.—Take a multiple arc of two branches, A C
B and A D B, and pass a current from a battery through it. The potential
at A is the same for both branches, also the potential at B. It falls off
Fig. 19.
along A C B, and also along A D B. Now by Ohm's law, since the current
in all parts of A C B is the same, the fall of potential in any part of A C B
is proportional to the resistance of that part. Hence, if we take two
points, C and D, at the same potential, then C must divide the resistance
of A C B in the same proportion as D divides that of A D B. Calling
the resistances of the parts P Q and R S, we have
— = — and R = — S;
S Q Q
and since C and D are at the same potential, if we join them by a galva-
nometer it will indicate no current. Hence, if we adjust the resistances
till there is no current given by the galvanometer, and let P, Q, and S be
known resistances given by a resistance box, we have R, which we suppose
to be an unknown resistance, to be measured. This method of arranging
so that the galvanometer shows no current, and thus deducing the
unknown quantity, is called a null method. It is the ordinary way of
measuring electrical resistances.
When in any such net-work two branches are so related (as the
A-36
DUFF.
battery and galvanometer branches are in this net-work) that a change
in one (such as suddenly " throwing in " the battery) does not affect the
current in the other, they are said to be conjugate branches.
Galvanometer Resistance.—If we wish to know the resistance of a
galvanometer we may simply put it in the unknown arm, R, in which case
we shall have to employ a second galvanometer, CD. But this second
galvanometer in C D is unnecessary, for all we need to see is that no
current flows through C D,—i.e., no change in the existing currents is
caused by connecting C and D, and this can be equally well seen by
watching the galvanometer in A C while we make and break, by means
of a key, the continuity of the simple wire joining C and D. This is
Thomson's method of finding a galvanometer resistance.
Battery Resistance.—Again, to find the resistance of a battery, we
may put it in A C and proceed as at first, with a galvanometer in C D
and battery in A E B. But, now, the battery in A E B is unnecessary,
for the battery introduced in A C keeps up currents in the net-work and
the battery in A E B can be simply replaced by a key ; and if we adjust
the resistances in the arms P, Q, and S till no effect on the galvanometer
in C D is produced by making and breaking with the key in A E B, then,
as before, we have
P
E = q S.
General Rule for Battery or Galvanometer Resistance.—Starting
with the original arrangement, to modify it, in order to find the resistance
of a galvanometer or battery, all we have to do is to put the battery or
galvanometer in the unknown arm, R, and replace the battery or galva-
nometer of the net-work by a key, and then seek a null adjustment, where-
upon we have
_P
R-QS.
52. Comparison of Electro-motive Forces.—The method we shall
employ is what is known as du Bois-Reymond's compensation method :
Let e be the electro-motive force of a battery to be measured, and E that
of a standard cell of known resistance, p. Join the poles of E by a lono-,
thin wire lying beside a graduated scale, by means of which we can read
ELECTRO-PHYSICS.
A-37
the lengths of parts of the wire. Also, join e in series with a galva-
nometer to A and a variable point, C, in A B. E will tend to produce a
current in A G C in the direction from A to C through G. On the other
hand, e will tend to produce a current in the opposite direction. Now,
by adjusting C along A B so as to increase or decrease the resistance, a,
of A C, we can send more or less of the current from E through A G C,
and so can adjust till the currents produced by E and e in A G C just
neutralize one another, which will be indicated by the galvanometer, G,
showing no deflection.
The reason no current goes through G is that, although the battery
E produces a slope of potential along A G C, the battery e produces an
equal and opposite one. The slope produced by E, or the difference of
potential between A and C, is the same part of the whole electro-motive
force of E that the resistance of A C—i.e., a—is of the whole resistance
of the circuit E A C B, i.e., p + a + b. Putting these two statements
together, we see that
e:E::a:p + a + b.
Now, a, p, and b are all known or measurable resistances; hence the
ratio e/E can be found.
Electrical Energy and Chemical Energy; Electrolysis.
53. Conduction in Liquids.—Unlike as electrical energy and chemi-
cal energy may be at first sight, still, they are both forms of energy, and,
therefore, capalbe of being changed into each other. Chemical energy
we know consists in the energy of certain attractions and repulsions.
Electrical energy consists in the energy of something in motion. The
currents we have been treating of so far were examples of the change of
chemical energy in Volta's cell into energy of a current of electricity. We
proceed now to consider the converse process,—the change of the energy
of an electrical current into chemical energy. The chief example is
what occurs in the passage of electricity through liquids.
As regards the conduction of electricity, liquids may be divided
into three classes :—
(1) Those that Conduct Like Solids.—This class contains all metals in the liquid state,
whether like mercury at ordinary temperatures or like iron fused at a high temperature.
(2) Those that Bo Not Conduct at all.—To this class belong pure water, pure hydro-
chloric acid, and generally all pure liquefied hydrogen acids (except HCN), fluid chlorine,
bromine and iodine, oils and resins (gases and vapors are also non-conductors; any decom-
position in them is due to convective discharge).
(3) Those that Conduct, but with Chemical Decomposition.—To this class belong dilute
acids and most simple binary compounds, i.e., compounds of two elements and compounds
derived from them by double decompositions.
54. Typical Case of Conduction with Decomposition.—The mean-
in o- of electrolysis has already been explained. By derivation, it means
the electrical decomposition of chemical compounds. Faraday was the
A-38
DUFF.
inventor of this and most of the following terms. A compound so
decomposed is called an electrolyte.
To explain the terminology, we shall take a typical case. In a vessel
containing zinc chloride (ZnCl2) suspend two platinum strips connected
with a battery. It will be found that zinc appears at one strip and
chlorine at the other. These strips are called electrodes, and the cell so
equipped is called a voltameter. The zinc is precipitated, and the
chlorine forms platinic chloride with the platinum. The decomposing
current enters at the strip connected with the copper or negative plate
of the battery, and this strip is called the anode. The current leaves at
the strip connected with the zinc or positive plate of the batteiy, and
this strip is called the cathode. These terms are taken from the analogy
of the motion of the sun, the anode being the place where the current
" rises " (ana hodos, or way up), and the cathode where it sets (kata
hodos, way down).
Thus it will be seen that the zinc travels with the current to the
cathode, and the chlorine against the current to the anode. These com-
ponents are accordingly called ions, from a Greek root meaning to go :
the ion that appears at the anode being called the anion, and that which
appears at the cathode the cation.
The positive current goes from the zinc to the copper and carries
zinc with it; hence, the zinc, or cation generally, is called electro-positive.
The negative current goes from the copper to the zinc and carries chlo-
rine with it; hence, the chlorine, or anion generally, is called electro-
negative.
Any reactions—following ordinary chemical laws—between the
primary products of electrolytic decomposition, the electrolyte, and the
electrodes are called secondary reactions.
55. Comparison of Simple Conductors and Electrolytes.— Contrast
of Resistance.—The resistances of electrolytic conductors are very hio-h
compared with those of simple metallic conductors,—e.g., pure H2S04
has seventy million times as great a specific resistance as pure copper.
Contrast of Temperature Effects.—The resistance of metals is
increased by rise of temperature,—of pure copper about § per cent, per
degree centigrade. The resistance of electrolytes is decreased by rise
of temperature,—of pure H2S04 about 4 per cent, per degree centigrade.
Faraday's Law of Conductors.—-Faraday established a law, to which
there seems to be no exception, viz., that all substances which in the
solid state are very bad conductors, but conduct on being melted, are
electrolytes, i.e., conduct with decomposition.
56. Faraday's Law of Electrolysis.—Faraday discovered that the
resistance to the separation of an element from a compound by an electric
current is the same, no matter what the compound, and depends merely
on the element. Hence the law of electrolysis : The amount of ion
that appears at an electrode in a second is equal to the strength of the
ELECTRO-PHYSICS.
A-39
current (supposed constant during a second) multiplied by a constant
called the electro-chemical equivalent of the ion. For example, if the
electro-magnetic unit of an electrical current (the ampere) flow per unit
of time (a second), it will liberate .000010352 gramme of hydrogen,
which therefore is the electro-chemical equivalent of hydrogen. We can
readily make out a relation between electro-chemical and chemical equiva-
lents ; for if, in the above case, a certain quantity of H is liberated at the
cathode, the quantity of CI combined with it (supposing the electrolyte to
be HC1) must appear at the anode. Now, every atom of H has combined
with it one atom of CI. Hence the' quantity of CI liberated must have
weighed more than that of H in the proportion of the atomic weight of
CI to that of H, i.e., in the ratio of 35.5 to 1. Again, in the above
typical case, the electrolysis of ZnCl2, since in each molecule there are
two atoms of CI to one of Zn (i.e., one of Zn is chemically equivalent to
two of CI; or, the " valency " of Zn is 2), only half as many atoms of Zn
will be set free by electrolysis as of CI; and since the atomic weights are
of Zn 65 and of CI 35.5, the weights liberated will be as %5 to 35.5.
Hence the electro-chemical equivalents of substances are proportional to
their atomic weights divided by their " valencies."
57. Polarization and Transition Resistance.—The decomposition
of the electrolyte, with the consequent deposition of the products of
decomposition on the electrodes, produces two effects.
Polarization.—In the first place, the change in the nature of the sur-
faces produced by the deposition means an alteration in the nature of the
contacts, and, therefore, a change in the electro-motive force of the
circuit. This will be true whether the products of decomposition are
simply deposited on the plates or combine with them chemically. The
new electro-motive force thus introduced is usually opposed to the main
electro-motive force, and is, consequently, called a " back " electro-motive
force, or electro-motive force of polarization. Its presence is shown by
sudden 1}' throwing the voltameter out of the main circuit and connecting
it with a galvanometer. It will then be found to act as a cell itself,
though its electro-motive force will, as a usual thing, very rapidly fall
away. The " back " electro-motive force is caused by the tendency of the
dissociated atoms to re-unite, and thus is a measure of the attraction of
these atoms, or of their " chemical affinity."
Minimum Electro-motive Force Required for Electrolysis.—It is
evident that the initial electro-motive force required to start electrolysis
must exceed the " back " electro-motive force that would be produced by
the process. Hence we have usually a lower limit to the electro-motive
force that will start electrolysis. For instance, a single Smee's cell, no
matter how large and close together its plates, will not electrolyze acidu-
lated water, for the back electro-motive force so produced is 1.47 V, which
is greater than the electro-motive force of a Smee cell. The current will
cease before it has produced any appreciable effects.
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DUFF.
58. Secondary Actions.—These imvy be classified as follows:—
(I) Appearance of Ions in Abnormal Molecular States.—The most
important example of this is the production of ozone along with oxygen
in the water voltameter. The amount produced is never large, but can
be readily recognized in the ordinary way by making it replace the iodine
in potassium iodide, setting free the iodine to act on starch. The amount
produced is largest when chromic and permanganic acids are elec-
trolyzed.
(2) Resolution of Compound Ions.—As an example, take the elec-
trolysis of oxyacids, e.g., H2S04. Here the ions are H and S04.
The latter, which has been named Oxysulphion, immediately breaks up
into 0 and S03.
(3) Reaction of Ions on Electrodes.—At the cathode, where the
metals are set free, the usual result is the formation of an alloy of the
metal of the cathode and the metallic ion. An example can be readily
obtained by electrolyzing copper sulphate with platinum electrodes. At
the cathode an alloy of copper and platinum is formed which penetrates
a considerable distance into the platinum. This union of the ions with
the electrodes takes place the more readily because the ions are in the
nascent state (§ 4). The oxygen liberated at the anode frequently unites
with the anode, even carbon becoming then oxidized to CO and C02.
(4) Reaction of Ions on Fluids at Electrodes.—Such nearly always
occurs unless the ions act on the electrodes themselves. Take, as an
example, the electrolysis of sodic sulphate or Glauber's salts,—Na2S04.
The immediate effect of electrolysis is to break it up, thus :—
Na2S04=Na2+S04.
The Naa appears at the cathode and reacts on the water there, thus:—
Na2 f 2H20 = 2NaHO + H2.
The S04 breaks up into 0 and S03. The former appears at the anode
and the latter unites with water, thus :—
S03+H20 = H2S04.
The presence of the H2S04 and NaHO can be readily indicated by
mixing some extract of red cabbage with the solution. If necessary, a
drop or two of acid is added till the whole is a dull-purple color. Then
the presence of the acid at the anode is indicated by its turning the
solution red, and that of the alkali at the cathode by its turning the
solution green.
59. The Electro-chemical Series.—The preceding may have sug-
gested that an element was always an anion or always a cation ; but this is
not so. The terms anion and cation are merely relative. It is found that
all substances can be arranged in a series, such that any substance is a
cation when combined with any lower in the series and an anion to any
higher; the beginning of the list being accordingly most electro-positive
ELECTRO-PHYSICS.
A-41
and the end most electro-negative. At the head of the list, or most
strongly electro-positive, stand K, Na, Li, Ba, etc. ; at the end I, Br, CI,
Fl, N, Se, S, O (for full list see Encyclopaedia Britannica,u Electrolysis ").
Thus the same substance may be sometimes an anion and sometimes a
cation, according to the position of its companion ion in the list.
60. Electric Osmosis, or Cataphoresis.—In ordinary osmosis (§6)
the liquids must be different, But even with the same liquid on both sides
of the porous partition the passage of an electric current from one side
to another will cause more liquid to diffuse in one direction than the
other, so that it will rise to a greater height on one side than on the other.
This is called electric osmosis, or cataphoresis. The latter name is
derived from the fact that the liquid is carried down (cata, down ; pherein,
to bear) with the current, i.e., more liquid passes by diffusion through
the partition in the direction of the current than in the opposite direction.
The process may be shown by using a weak solution of starch and a weak
solution of iodine separated by a porous partition. The current, on
passing from the iodine to the starch, will carry some of the former with
it, thus coloring the starch by chemical reaction with the iodine. This
o*^^c?^cf«o8
C»O»O»O»O»O»O0O»
0«0«0«0«0«0«0«0 4
CM 0» 0» 0# 0# CM CM
Fig. 21.
• an atom of hydrogen; O an atom of chlorine; •---> dlreotion of current.
process plays an important part in medical applications of the electric
current, or the process known as cataphoric medication.
61. The Mechanism of Electrolysis—Grotthuss and Clausius.—
This process of electrolytic conduction is at first sight somewhat parodox-
ical. For, though the current passes from electrode to electrode, and
must, therefore, pass through the liquid, yet the chemical evidence of the
current, viz., decomposition, only appears at the electrode. Does, then,
the current produce no decomposition in the body of the liquid?
Grotthuss's Theory.—The answer given by Grotthuss is that there is
decomposition everywhere, but, whereas there is immediate recomposition
in the body of the liquid, there is no such recomposition at the electrode,
and so the components appear there. This theory may be represented
thus (Fig. 21) : In the electrolysis of HC1 the first thing that happens
is a wheeling of all the molecules into line, all the H atoms pointing
toward the cathode and all the CI atoms toward the anode. Then each
molecule ruptures and each atom turns to the dissimilar atom on the
other side and combines with it, forming new molecules, but leaving free
atoms of CI at the anode and free atoms of II at the cathode. Again the
A-42
DUFF.
molecules wheel around into position and again the process is repeated,
and so on.
This theory will evidently explain (1) the appearance of the products
of decomposition at the electrodes and (2) Faraday's law as regards a
single electrolyte. It does not, however, explain (3) the transference of
the electricity nor (4) why the same amount of an ion should be separated
from different electrolytes by the same current.
Berzelius's Extension of the Theory.—The extension made by Ber-
zelius is that on the union of H and CI to form HC1 electrical distribu-
tion takes place in a similar way to that of magnetism in a bar magnet,
H becoming the positive and CI the negative pole. When the anode has
become sufficiently highly charged with positive electricity its attraction
on CI becomes greater than that of the H atom, and so the HC1 molecule
is decomposed. Helmholtz further suggested that each atom carries with
it a certain definite charge. If the atoms on decomposition cling to their
electrical charges these latter cannot be passed around to the other plate,
and may accumulate and partly neutralize the attraction of that plate for
the ions. This gives rise to an electro-motive force of polarization.
62. Electrolytic Resistance and Ohm's Law.—The measurement
of the resistance of an electrolyte is a matter of considerable difficulty,
chiefly owing to the complications introduced by the polarization electro-
motive force, which, so far as weakening the current is concerned, is
equivalent to an added resistance. The means resorted to have been
these :—
(1) Horsford used a voltameter in which the electrodes were at measurable distances,
which could be altered. The plates were brought nearer together by a known amount, and
the current kept constant by inserting a known resistance from a resistance-box. The cur-
rent being constant, it was assumed the polarization was, and so the added resistance was
the resistance of a thickness of the electrolyte equal to the distance by which the plates
were brought nearer.
(2) Beetz employed the principle that carefully amalgamated zinc plates in a neutral
solution of zinc sulphate are not polarizable, and so measured the resistance of zinc
sulphate.
(3) Paalzow inclosed the electrolyte in a siphon which dipped into vessels of porous
earthenware filled with the electrolyte. Those porous vessels were immersed in beakers
filled with zinc sulphate, at the bottoms of which were large amalgamated zinc discs form-
ing the electrodes. Thus there would be no polarization except possibly at the surface
of contact of the liquids, and that would be small.
(4) Kohlrousch and Nippoldt used rapidly alternating currents, and so the ions would
recombine as fast as separated and no polarization would ensue.
By all these means Ohm's law has been fully proven to hold true for
liquids as well as for solids.
63. Secondary or Storage Cells.—We have seen that, in general, the
passage of a current through a voltameter alters the electrodes by sec-
ondary actions between the ions and the electrodes. Thus, if before the
passage of a current the electrodes were quite similar in substance, after
the passage they are dissimilar; and therefore the voltameter has become
ELECTRO-PHYSICS.
A-43
a voltaic cell and can be detached and used as such until, by the reverse
current started, the work done on the electrodes by the original current
is undone, or the electrodes are discharged. A cell so constructed is
called 'a secondary cell, because it is not of itself primarily a generator
of a current, but only subsequent to the passage of a current through
it. Secondary cells are also called storage cells, but it is not meant
thereby that they store up electricity. What is meant is that they store
up energy, namely, in the chemical form, and that this energy can be
reproduced as the energy of an electric current. They are also frequently
called accumulators. Any voltameter in which similar electrodes are
rendered dissimilar by the passage of a current becomes a secondary
cell, but only a few have been so constructed as to maintain a current for
any considerable length of time.
Grove's Gas-Battery.—If acidulated water be electrolyzed in a closed
voltameter with long electrodes of platinum, so that the gases are retained
surrounding the electrodes, after the decomposition has proceeded for
some time the voltameter has become a charged secondary cell, and can
— 5?- ^
Fig. 22.
Fig. 23.
be used as such until all the decomposed gases have disappeared by
decomposition. Or the gases may be otherwise prepared and then in-
troduced.
Planters Secondary Cell.—In Plante's secondary cell the electrodes
are lead plates immersed in dilute H2S04. In its original form the
preparation of the plates, or the " formation " of the cell, as it was called,
was a troublesome process. First, a current was passed through it till
the surface of the anode was oxidized into Pb02 (Fig. 22). Then the
current was reversed, whereupon the Pb02 was reduced, leaving that
surface covered with " spongy" lead, and covering the surface of the
other plate with Pb02. The current was again reversed, and so on for
weeks, until the lead surfaces had been acted on and rendered " spongy "
to some depth. The plate that last served as anode remained deeply
coated with Pb02.
If the cell be now used to generate a current, this current will be in
the direction from the peroxidized plate to the plain lead plate (Fig. 23).
The chemical changes will consist in the reduction of the Pb02 to PbO?
and the oxidation of the Pb plate to PbO ; so that the two plates become
A-44
DUFF.
similar. When this state is attained the cell is " run down." It must then
be " re-charged," which consists in sending a reverse current so as to
again peroxidize one plate and reduce the other to spongy lead, and thus
the cell is again charged. (In this simple account we have neglected the
presence and action of PbS04 on the plate. Chemically it is negligible,
but mechanically it seems to serve the important purpose of separating
the Pb02 from the Pb below it, and so preventing the Pb02 from being
reduced by mere " local action " between the Pb02 and the plate on which
it is, and thus giving no current.)
Faure's Modification of Planters Cell.—There is a great waste of
energy in the process of "formation" of Plante's cell. To avoid this,
Faure coated the plate to begin with with minium, or red lead,—Pb203,
or PbO.Pb02. Then, on charging by passing a current we get H2 set free
at the cathode and 0 at the anode, and the reactions that take place
are :—
At cathode, Pb203 + 3H2=3H20 + 2Pb.
At anode, 3Pba03 + 30 =6Pb02.
Thus we shall have one plate peroxidized and the other spongy lead, and
the cell is charged ready for use.
The chief difficulty in this cell is to make the minium adhere to the
plates. For this purpose the plates are gridironed and the minium
packed in the interstices in the lead, or some other similar device is
resorted to.
The electro-motive force of such a cell is over two volts ; so that to
charge a single cell with primary batteries at least three Bunsen cells
are required. If all the storage batteries during charging are connected
abreast, any number can be charged by a few Bunsen elements (requir-
ing, of course, proportionately longer time), and then they can be con-
nected in series, and so a much higher electro-motive force obtained than
from the charging battery.
Electrical Energy and Heat Energy.
64. Their Interchangeability.—Heat, being a form of energy, is
interchangeable with other forms of energy, and among them with elec-
trical energy. Of the change of electrical energy into heat energy we
have an example in every current of electricity. For heat is the form
of energy generated whenever work is done against frictional resistance;
and as electrical resistance is of the nature of friction, and all conductors
offer some resistance to electric currents, heat is generated by every
current. We shall first discuss the change of electrical energy into heat
energy, and then the change of heat energy into electrical energy. The
currents obtained by this latter process are usually called thermo-electric
currents.
ELECTRO-PHYSICS.
A-45
65. Development of Heat in a Circuit.—A current of electricity
generated by a voltaic cell is capable of doing work, such as turning an
electric motor. But if the current be merely passed through a wire
doing no work, it must produce heat, since the same amount of chemical
energy is used up in the cell, and it must be reproduced in some other
form of energy.
It can be shown without difficulty that the heat so produced in a wire
varies as the square of the current and the first-power of the resistance
conjointly. For by definition the difference of potential between the
ends is the work done in carrying a unit of positive electricity from one
end to the other. Hence, if the difference of potential or electro-motive
force be E and the current be C, then, since C is the number of units of
electricity that pass in unit time, the work done in unit time is W = EC ;
and by Ohm's law C = |, or E = CR ; hence, W = C2R. If C and R
be in C. G. S. units, W will be the number of units of heat energy pro-
duced per second.
Thus the heat energy produced depends only on the current and
resistance. Hence, to avoid loss of energy by heating the conductors,
a small current and low resistance is to be used. This is the secret of
electrical transmission of power. The power is transmitted as an elec-
trical current of small current-strength, though high electro-motive
force, and then when it is to be used it is transformed into a larger
current of lower electro-motive force.
Where heat is to be developed high resistance is used. In electro-
cautery the surgeon wishes to burn off a growth by a heated wire, and so
he uses not silver, which, for one thing, would have
'too small a resistance, but platinum, which has a
higher resistance.
Again, incandescent lighting depends on the heat-
ing to incandescence of a carbon filament of high re-
sistance. In the arc-lamp the resistance is in the
carbon vapor between the carbon points, and the
light is produced by this incandescent vapor, but
chiefly by the heated ends of the carbon rods. fig. 24.
66. Production of Electricity from Heat.—We
now proceed to the converse process,—the transformation of thermal
energy directly into electrical energy. The first to discover the possi-
bility of this was Seebeck. He found that in a circuit of only two metals
a current can be produced by simply heating one junction to a higher
temperature than the other. This can be very readily shown by winding
the ends of a copper and an iron wire together and then heating that
junction, while the other ends are connected to a galvanometer. A cur-
rent will be found to flow in the direction from copper to iron through
the hot junction. The same thing can be shown still more strikingly by
using bismuth and antimony, when the current will be found to flow from
A-46
DUFF.
bismuth to antimony through the hot junction. Similar phenomena will
be produced by using any pair of metals.
Thermo-Electric Power.—To render our ideas more definite, in de-
scribing the current or electro-motive force produced by any such couple
of metals, we must specify the difference of the temperatures at which the
junctions are. Moreover, the electro-motive force may depend not only
on the difference of temperature of the junctions, but also on their actual
temperatures. Hence, we define the thermo-electric power of a couple at
a specified temperature as the electro-motive force produced by keeping
one junction ^° C. above and the other ^° C. below that temperature.
With this definition it will be found that the thermo-electric power is
different at different temperatures (§ 69).
67. Thermopiles and Thermo-Electric Batteries.—With a thermo-
electric couple, then, we have a means of generating electric current
directly from heat. But the electro-motive force of such a current is
very low,—for a Cu-Fe couple with one junction 1° C. above the rest
of the circuit it is only .0000137 volts, and for a Bi-Sb couple it is
.000117 volts.
But we can obtain a much greater electro-motive force in the fol-
lowing way: Instead of taking a single piece of Bi and a single piece
Bi Bs B3 B4
Fig. 25.
of Sb, take a number of pieces and connect them up alternately as in
the diagram. Then, if a B junction be heated, it is evident, by the rule
above, the current will be in the direction of the arrow; but if any A
junction were heated, the current would be in the opposite direction.
Hence, to get a greatly-increased electro-motive force, we heat all the B
junctions, keeping all the A junctions at the ordinary temperature.
Thus, by multiplying the number of junctions, we can multiply the
thermo-electro-motive force to any desired extent.
Such thermo-electric multipliers have been made for different pur-
poses in two different forms. One form—the thermopile—is used as a
very sensitive detector of heat. It consists of a circuit such as described,
except that the strips are packed together, with strips of paper or gutta-
percha between them for insulation, into a box, so that all the A junc-
ELECTRO-PHYSICS.
A-47
tions are exposed at one end and all the B junctions at the other. When
either end is exposed to a source of heat, a current will be indicated by a
sensitive galvanometer in circuit with the thermopile.
The Thermo-Electric Battery.—The above arrangement can also be
employed to generate currents. For this purpose the cold junctions
must be kept at a low temperature,—e.g., by immersion in ice; and the
hot junctions heated to a high temperature,—e.g., by immersion in boilino-
water, or by heating by gas-burners or some similar means. Such bat-
teries have been made by Pouillet, Becquerel, Clamond, and others,
and can be used for such purposes, as electro-cautery and telegraphy, as
do not need a very considerable electro-motive force, but only a large
current.
68. Heating or Cooling of Junction by Passage of Current.—
We have seen that in any part of a conductor heat is generated by the
passage of a current. Such heat is due
simply to the frictional resistance the con-
ductor offers to the passage of a current. We
have also seen that, conversely, if one junc-
tion of a circuit of two different metals be
heated, a current is produced by the absorp-
tion of heat. But the former is not quite
the converse of the latter. The proper con-
verse of this would be if heat could be pro-
duced at the junction by the passage of a
current. This can really be done, as was discovered by Peltier. His
discovery was this : Pass a current through a junction of two different
metals; then heat will be disengaged if the current be in opposition to
the direction in which a current would be produced by heating the
junction, and heat will be absorbed if the current be in the direction of
the current that would be produced by heating the junction.
For example, if a current be passed through a Bi-Sb junction
from Sb to Bi, the junction wrill be heated by disengagement of heat; if
the current be passed in the opposite direction, from Bi to Sb, the junc-
tion will be cooled by absorption of heat.
There will be no difficulty in remembering these facts if it be remem-
bered that, both in the Seebeck effect and in the Peltier effect, a current
from Bi to Sb is alwa}Ts attended with absorption of heat.
69. Xeutral Point and Reversal.—If we connect two Cu wires to
a galvanometer and also wind their free ends around an iron wire, A B
(Fig. 26), we can verify the following phenomena discovered by Cumming.
Heating the junction, B, a current will go in the direction ^f, as shown by
the galvanometer. It will increase heat at a decreasing rate : when B is
at 260° C. it will become steady, and then will decrease until at 500° C.
(supposing A to be constant at 20° C.) it will become zero, and then will
turn in the opposite direction.
A-48
DUFF.
Now, it will be noticed that the temperature of reversal is as much
above 260° C. as the temperature of A is below it. This would be true
no matter what the temperature of A. Thus,
A being at 20 ° (= 260 — 240°), reversal occurs at 500 ° (= 260 + 240°).
" " " 100 ° (=260 —160°), " " " 420 ° (= 260 + 160°).
« « "250 °(=260— 10°), " " " 270 ° (=260+ 10°).
" " "259JQ (=260— |°), " " "260^° (=260+ £°).
Now, by remembering the definition of thermo-electric power at a
certain temperature as the electro-motive force when one junction is half
a degree above and the other half a degree below that temperature, the
last result in the table is readily interpreted as meaning that at 260
degrees the thermo-electric power of a Cu-Fe couple is zero, or the metals
are neutral to one another. Hence, 260 degrees is called the neutral
point for an Fe-Cu couple.
Similar results hold true for all other couples. Each couple has its
neutral point or point of zero thermo-electric power, and when one junc-
tion is a certain number of degrees below the neutral point reversal will
occur when the other is an equal number of degrees above it.
70. Thomson Effect.—From the above results Sir William Thom-
son reasoned as follows : When one junction is kept at the neutral tem-
perature and the other at a lower temperature, there is undoubtedly a
current, viz., from Cu to Fe through the hotter junction. Now, since
in a junction at the neutral temperature the metals are neutral to each
other,—i.e., show no difference of electro-motive force,—the Peltier effect
is also at that temperature zero, i.e., no heat would be absorbed or dis-
engaged by passing a current through a junction at that temperature.
Hence, there is no heat absorbed at the hot junction. Again, there is
not only no heat absorbed but even heat given out at the cold junction.
Whence, then, the energy of the current ? It must be that heat is taken
in along the wires themselves. Now, undoubtedly heat is not taken in
when a current passes along a wire all parts of which are at the same
temperature ; so that the absorption of heat along the wires must be in con-
sequence of their slope of temperature from their hot to their cold ends.
So Thomson was led to the very important conclusion that metal
conductors can be divided into two classes. If a conductor belong to the
first class a current passing from hot to cold parts along it will absorb
heat. Iron belongs to this first class. If the conductor be of metal
belonging to the other class, a current on passing from hot to cold will
tend to disengage heat. Cu belongs to this second class.
Thus, in Cu the current tends to warm the colder parts and thus
equalize the temperature throughout, just as a current of water passing
from a hot part of a pipe to a cold part would, and in iron the reverse
happens. Using this analogy the whole thing is conclusively summed
up in the statement that in Cu electricity has a positive specific heat
(i.e., gives out heat on cooling), while in Fe it has a negative specific
heat (i.e., takes in heat on cooling).
ELECTRO-PHYSICS.
A-49
Radiant Electrical Energy.
71. Magnetic Field of Current.—We have already (§ 38) touched
on the effects produced by a current beyond the conductors themselves
in which it flows. We shall now take up briefly this radiation of energy
by the electric current. For fuller details of parts bearing direcely on
medical applications the reader is referred to the section on faradic
current.
The facts on which we founded the statement that the current had a
magnetic field were these :—
(1) Magnet Moved by Current.—A current in a conductor will deflect
a freely-suspended magnet-needle near it.
(2) Magnet Produced by Current.—A spiral current will make a
magnet of a core of iron inclosed in the spiral.
We shall first take up the converses of these.
72. Momentary Current Produced by Motion of Magnet.—The'
converse of (1) above would be the generation of a current by the move-
ment of a magnet. This can be shown by
inserting a bar magnet into a coil of wire in
circuit with a galvanometer and then with-
drawing it. It will be found that both at
insertion and withdrawal a momentary cur-
rent flashes through .the coil, and the direc-
tions of these currents are determined as fol-
lows : If the bar were not already a magnet,
to make it into a magnet with its poles in
the direction of the actual magnet would
require a current in a definite direction in Fig. 27.
the coil. Let us call the current that would
thus produce the magnet a direct current, and one in the opposite direction
a reverse current.
Then we may state the above result as follows: The insertion of a
magnet into a coil starts a reverse current, and its withdrawal a.direct
current.
The reader will carefully notice that these currents are only mo-
mentary and die down almost immediately, though its own inertia may
keep the galvanometer-needle swinging.
73. A Current Equivalent to a Magnet.—The converse of (2)
above would be the moving of a circuit carrying a current by a magnet.
This can be shown as follows : If a small coil consisting of several turns
of copper wire have its ends inserted through a large cork and soldered
to strips of copper and zinc and the whole be floated on acidulated water,
it is easily shown that the coil is attracted and repelled by a bar magnet
just as a small floating magnet would be. (Fig. 27.) It will, in fact, be
equivalent to a very short magnet whose axis is perpendicular to the
plane of the coil, and whose north and south poles can be found by the
4
- -
C« Zt t
A-50 DUFF.
rule that the south to north direction of the axis is related to the direction
of the current as the thrust to the twist of a right-handed screw. Such
an arrangement is known as De La Rive's floating battery.
Hence, not only will a current make a magnet, but it is itself equiva-
lent to a magnet. The form of the equivalent magnet depends altogether
on the form of the current. Taking a long spiral coil of wire it is equiva-
lent to a long bar magnet whose north pole is where the current leaves
the magnet if it be a right-handed spiral, and vice versa if left-handed.
74. Momentary Current Produced by Motion of Another Cur-
rent.—We have now seen that a moving magnet can generate a mo-
mentary current in a conductor, and, further, that a current in a circuit
is equivalent to a magnet. Hence it seems probable that a current in
one moving circuit may generate a current in another circuit.
That this is really so can be readily seen by inserting a spiral carry-
ing a current into another spiral in circuit with a galvanometer and then
CA
K
i
Tb
DB
Fig. 28. .
withdrawing it. In both cases momentary currents will be observed,
whose directions are given by the above rule in § 72.
Such momentary currents are called induced currents.
75. Momentary Current Produced by Varying Another Current.
—We do not need, as above, to move the circuit carrying the influencing
current. It will serve the same purpose if we leave the influencing cir-
cuit at rest, and simply start and stop a current in it. This will be
equivalent to having a steady current in it and making it approach and
recede from the second circuit.
On starting the current, then, in the inducing or primary circuit, we
will have an oppositely directed current induced in the influenced or
secondary circuit, and on stopping the current in the primary we will
have a direct current induced in the secondary circuit. The above phe-
nomenon is often called mutual induction. It can be studied by laying
two long wires side by side, putting one in circuit with a battery and
key, and the other in circuit with a galvanometer. On making with
the key so that a current starts in the direction A B, the galvanometer
will give a throw indicating a momentary current in the direction "5~u.
ELECTRO-PHYSICS.
A-51
On breaking with the key the galvanometer will give a throw indicating
a current in the direction 7Td"- (Fig. 28.)
76. Self-Induction—But inductive effects are possible without a
second circuit. Two different parts of the same circuit may act on one
another, e.g., two different turns in the same spiral. A current rising
in such a spiral will act inductively on itself, tending to produce a reverse
current whose effect will be shown in a retardation of the rise of the
main current. This is the self-induced current at " make."
Again, on stopping a current in a circuit, a momentary direct current
will be produced, and its effect will be manifested in a tendency to prolong
the life of the dying current. It is obvious that the effect of both, then,
is to prevent either the sudden starting or the sudden stopping of a cur-
rent of electricity. A similar effect is produced in a current of liquid
by the inertia of the matter. Hence,
the above phenomenon of self-induc-
tion is sometimes referred to as the
inertia of electricity. Wc shall attempt
to explain later the real cause of it.
77. Ruhmkorff's Induction Coil.
—A very important peculiarity of in-
duced currents is that by using suitable
secondary circuits wTe can get either a
much higher or a much lower electro-
motive force than that of the primary,
attended by a much smaller or much
greater current, respectively. This is of great importance in apparatus
which employs induced currents, such, e.g., as Ruhmkorff's induction
coil. An induction coil consists essentially of a primary coil or bobbin,
which can be slid into a secondary coil. The primary coil usually
contains an iron core, to heighten the effect. Subsidiary parts are an
interrupter and a condenser. In accordance with the above remark, the
secondary is made of a large number of turns of small wire, so as to
largely increase the induced electro-motive force, and the primary is
made of a few turns of stout wire, so as to afford a large current and
decrease the effects of self-induction. On rapidl}' making and breaking
the current in the primary, a succession of momentary currents, alter-
nately reverse and direct, will traverse the secondary. This " make and
break " can be best done automatically by an interrupter
The Interrupter.—A bundle of soft-iron wires is inserted in the
primary coil. When the current passes, this bundle becomes an electro-
magnet, and attracts a piece of soft iron attached to a vertical spring, S.
Parallel to the spring is an upright, A B. through which passes a screw,
which presses against the spring, and the current of the primary is led
through this upright, screw, and spring. On the breaking of the current
by the attraction of I the bundle ceases to be an electro-magnet, and so I
Fig. 29.
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DUFF.
is released, whereupon the circuit is again completed and again the cur-
rent passes, and I is attracted. Thus we have a succession of momentary
currents in the primary. (See Fig. 29.)
The Condenser.—This consists of sheets of tin-foil separated by di-
electric sheets of paper soaked in paraffin. It is connected with the pri-
mary in such a way that (1) when the primary is broken the electricity of
self-induction flows into the condenser, and so causes no spark at the in-
terrupter ; and (2) when the primary is made the condenser is discharged
into it, and so causes the primary to grow very slowly, and thus greatly
decreases the spark in the secondary at making of the primary.
The net result is that the currents induced in the secondary at make
I------------/,--------------1
Fig. 30.
of the primary become very negligible compared with those produced at
break of the primary, and so we have in effect a succession of currents
in the same direction and of very high potential.
78. Magneto-Electric Machines.—So far as the generation of a cur-
rent in a coil of wire is concerned, it makes no difference whether we move
the magnet and keep the coil stationary or move the coil and keep the
magnet stationary. The only thing requisite is relative motion.
In a magneto-electric machine two parallel bobbins of wire, each con-
taining a soft-iron core, are whirled rapidly around an axis midway be-
tween them. Thus the bobbins come alternately in front of the poles of
a poweful permanent magnet, and thus the cores are rapidly magnetized
alternately in opposite directions, and so on in a circuit including both
the bobbins alternate currents are generated in rapid succession. A
commutator attached to the rotating axis reverses the currents at
ELECTRO-PHYSICS.
A-53
every half revolution, so that all the currents are turned in the same
direction.
79. Attraction and Repulsion of Currents.—Since magnetic poles
attract and repel each other, and currents even in straight conductors
have magnetic fields of force, it is natural to expect that currents will
exhibit attractions and repulsions.
Ampere was the first to establish the laws of such attractions and
repulsions. His conclusions as to all currents can be readily verified by
such a simple apparatus as is shown in Fig. 30.
It will then be found that the currents attract each other where run-
ning in the same direction and repel where running in opposite directions.
The laws for oblique currents'can be readily deduced from the fore-
. going. For if two parallel currents be shifted so as to become somewhat
inclined to each other, then they will both run away from, or one away
from and the other toward, the common apex,
according as they were formerly, in the same or in
opposite directions, respectively. Hence, oblique
currents attract if both run away from the common
apex, and repel if one runs away from it and one
toward it.
80. Ampere's Theory of Magnetism.—Before
proceeding to consider what electricity is, we may
first get magnetism out of the way by reducing it
to electricity, and here we are treading on pretty fig. 31.—North Pole.
firm ground. For it will be remembered that in § 34
we saw strong reason for believing that even the ultimate particles of a
magnet were magnets also. Now, absolutely all the behavior of a magnet
can be imitated by an electrical current in a circle or helix. Hence we
have a strong hint that the ultimate particles of a magnetic substance
contain little circulatory currents, which, just like larger ones, ape the
behavior of a magnet.
It will be remembered that the magnet to which a circular current
was equivalent had its axis perpendicular to the plane of the current.
Hence, according to this theory magnetization consists in making these
molecular currents wheel all facing the same way with their planes per-
pendicular to the length of the magnet which they make up, i.e., with
their planes perpendicular to the lines of magnetic force.
We cannot take space to enumerate the numerous, almost conclusive
arguments for this theory. One only we shall mention,—a remarkable
phenomenon discovered by Faraday. Light that has its vibrations reduced
to one plane is said to be plane polarized. Now, there are certain crys-
tals and solutions that have a peculiar effect on such light, namely, they
rotate the plane of polarization. Faraday discovered that when plane
polarized light was passed through certain substances (notably, " heavy"
glass) which were in a strong magnetic field, the direction of the rays of
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DUFF.
light being the direction of the lines of force, a similar rotation of the
plane of polarization took place. But there was a remarkable difference
between the two cases. If the light were reflected back through the crys-
tals its twist would be taken out, but if the same thing were done with
the light rotated magnetically the twist would be doubled. This can only
be explained on the supposition that in the magnetic field there is some
kind of rotation going on around axes parallel to the lines of force.
What is Electricity'?
81. Nature of Answer.—It is well to realize at the outset exactly
what answer may be expected to the question, " What is electricity ?"
Since certain famous experiments performed by Dr. Hertz, of Germany, a
few years ago, it has been a common popular mistake to suppose that we
know what electricity in its essence is. This is as serious a mistake as
to suppose that the establishment of the kinetic hypothesis tells us what
matter is. What each does is simply to let us have a faint glimpse into
the mechanism by which electrical and material phenomena are brought
about; that is all. About what electricity is we know as yet practically
nothing, and probably will never know fully. But we do now know posi-
tively something of the way in which certain electrical phenomena, chiefly
those treated under the head " Electrical Radiation," are brought about.
In a word, what electricity is has only been answered by certain dim
speculations ; but assuming a something, we know not quite what, called
electricity, we can pretty clearly explain certain electrical phenomena.
It would, perhaps, be more satisfactory to take up the known and
clearly settled first, and then indicate the unsettled speculations ; but
this would necessitate an order that would be likely to confuse the
reader, so we shall take the subject up in the logical order, and take care
to point out the known and the doubtful.
82. Electricity is not Energy.—A common answer to the question,
" What is electricity ? " is, " Electricity is a form of energy." In preced-
ing sections we have frequently spoken of electrical energy, or energj^ of
electrification, or energy of the electrical current. But none of these
phrases imply that the electricity itself is energy, just as though two
masses attracting each other gravitationally (such as the earth and the
moon) form a system having a certain amount of potential energy, and
matter in motion has kinetic energy, yet in neither case is the matter
itself energy. Similary, two so-called charges of electricity attracting
and repelling each other form a system having potential energy and
electricity in motion has kinetic energy ; yet in neither case is the elec-
tricity itself energy.
Again, the energy of a charged conductor is the work we would
have to do in charging it. Its potential, V, is the work done in bringing
unit charge up to it from a place of zero potential. The work done in
bringing Q units up will then depend on the product Q V. Hence, the
ELECTRO-PHYSICS.
A-55
energy of the charge is proportional to the product QV. Hence, it is
obvious that the charge Q itself cannot be energy. In this respect it
differs markedly from heat. The energy of a charge of heat does not de-
pend upon its temperature; it is the same whether it is heat in a warm
body or heat in a cooler body. The heat itself is energy.
83. Electricity is a Thing, for it is Conserved.—In § 3 we stated
that the test of a thing was whether it was conserved or remained always
the same in quantity. If all the cases of electrification and flow of elec-
tricity that we have discussed be carefully considered, it will be found in
all cases that electricity will stand this test. In the first place, this is
evident as regards a voltaic current, for no such current will flow except
in a closed circuit. If the circuit be not completed, but the gap be not
too great, the current will jump across the gap, and so complete the
circuit. In any other case there will be no flow. The electricity, in
fact, behaves as a perfect and incompressible fluid.
In the second place, as regards a static charge of electricity,—as, for
instance, a charge given to a Leyden jar from an electric machine,—it may
be objected that here we have, for the time being, a flow into the con-
denser without any complete circuit. But here, too, we can show that
there is a circuit completed, and that the electricity still retains its
similarity to an incompressible fluid.
84. In Charging a Conductor Electricity is Elastically Strained
Outward.—In § 29 we saw a remarkable parallel between the charge and
discharge and the various residual charges and discharges of a Leyden
jar, on the one hand, and the phenomena shown by elastic bodies when
distorted, on the other hand. This in itself was enough to strongly sup-
port the view that the charging of such a jar meant setting up an elastic
strain in the dielectric which separates the coatings, and that its discharge
meant relieving this strain. Thus, the most important part in the whole
phenomena is played by the dielectric.
To enable us to think of the matter more clearly, we shall use the
following analogy, which represents the state of affairs very well and
may be, probably is, much more than a mere analog}'. We shall think
of electricity as an incompressible fluid, filling all space, and a dielectric
as a kind of elastic jelly in which what we call electricity is imbedded
or entangled. Now, a property of such an arrangement would be that,
if we tried to displace the electricity, we would meet with a certain
amount of elastic resistance from the jelly, and when we released the
particles from the distorting forces they would be immediately drawn
back nearly to their original positions by the elastic force of the jelly.
This is what takes place in charging a conductor. Electricity is forced
into it, but acts like an incompressible fluid, so that in the conductor
itself no change of density of the electricity is produced, but at the
surface electricity is forced out into the dielectric, setting up such a
strain as we have referred to above. This, it will be observed, accounts
A-56
DUFF.
for what we referred to in § 21, that electricity resides only on the sur-
faces of conductors. For we conceive of a conductor as permitting the
electricity to flow freely through it, so that in the conductor there is
neither strain nor condensation. Hence, in the body of the conductor
there will be no change produced and the charge will only be manifested
as elastic strain at the surface.
But the electricity in the dielectric is incompressible, so that when
any layer of it is displaced outward it must displace the next layer out-
ward, and so on. Where, then, will the process stop ? Evidently, it will
only stop when the strain reaches the surface of another conductor from
which electricity has been withdrawn. Some electricity will, conse-
quently, be forced into the conductor. But how does this conductor
come to have a deficiency ? Electricity must have gone from it to some-
where. If the whole process has been confined to these two conductors,
evidently what has been taken from B must have gone to A. In other
Fig. 32.
words, A has been charged positively and B negatively, and again the
flow has been in a closed circuit from B to A by the machine and back
to B by the dielectric. So A and B each contain as much electricity as
at first, but the dielectric is in a state of strain, which will immediately
force the electricity back from A to B, if we connect the two by a
conductor.
85. Static Electrification is Potential Energy.—In § 8 we saw
that an elastic spring, when stretched, tended to shorten and so do work,
and so it possessed potential energy. In the same way, the strained
dielectric separating two charged conductors is in a state of elastic dis-
tension, and contains, therefore, potential energy.
86. Paramount Importance of the Dielectric—No Action at a
Distance.—The reader will notice that in the preceding the leading role
is played by the dielectric or the non-conducting medium between charged
bodies. It is, in fact, the dielectric that is charged, not the conductors.
This recognition of the part played by the dielectric is what distinguishes
the old one-fluid and two-fluid theories from the theories we now adopt.
The older theories viewed the charges on two conductors as acting on
one another directly at a distance, i.e., without any assistance from the
ELECTRO-PHYSICS.
A-57
intervening medium. From the time of Newton down, physicists have
disbelieved in this action at a distance, though admitting it as a mathe-
matical fiction. They believe now that when any two bodies act on one
another,—viz., two conductors charged with electricity, two heavenly
bodies (such as the sun and earth), or two magnets,—in all those cases
the action is to be accounted for by considering what is happening in the
intervening medium.
Direct action at a distance and action by an intervening medium
should differ in this wray : If a body acted on another directly at a dis-
tance, such action should be propagated instantaneously; whereas, if the
action took place by means of the intervening medium, such transmis-
sion should not be instantaneous, but should have a finite velocity. It
becomes, then, of the utmost importance to settle whether electrical
effects are propagated with a measurable finite velocity. How this has
been settled will be explained later (§ 92).
87. Function of a Machine, Battery, or Dynamo.—We see, then,
that a circuit of wire is just as full of electricity when no current is
circulating in it as when a current is circulating in it. The difference
lies in the fact that in the latter case electricity is being pumped around
the circuit by means of the " generator," as it is mis-called.
In the case in which a condenser is being charged, part of the flow
consists in elastic displacement through the dielectric. This displace-
ment will continue until the elastic reaction is equal to the displacing
force, when the flow will stop, or until the strain in the dielectric rup-
tures the dielectric, producing a disruptive discharge.
88. Process of Conduction in Solids.—In a dielectric we can set
up a state of strain with a tendency to spring back. In a conductor,
though we may attempt to set up such a strain, it will be unavailing. It
will break down as fast as set up, and thus the electricity will be handed
on by a series of instantaneous disruptive charges, constituting a con-
tinuous flow in the conductor.
For clearness we may liken the process to the flow of water in a tube
full of marbles. It will experience a frictional resistance to flow, and
Ohm's law if interpreted tells us a remarkable thing about this resist-
ance. For by Ohm's law the force urging the flow is proportional to the
flow. Now, if there were no force opposing the flow the flow would not
go on at a steady rate, but at an accelerated pace; or, if the force urging
the flow were greater than the force opposing the flow there would still
be a resultant force forward, and still an acceleration of the pace. Now,
since there is no acceleration of the pace after the flow has become steady,
it is evident that the urging and retarding forces must be equal; and since
the urging force is proportional, accurately to the flow (which is Ohm's
law), the retarding force must also be accurately proportional to the flow,
or the frictional resistance is proportional to the first power of the speed.
If we contrast this with the frictional resistance of the air to a falling
A-58
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body, we will see that it is a remarkable result, for at low speeds the air
offers a resistance proportional to the first power of the speed ; at higher
speeds the resistance is proportional to the second power, and at still
higher to the third power. But in electrical flow the resistance is always
proportional exactly to the first power of the speed.
Now, when work is done against friction heat is produced. It is
readily seen that the heat so produced when a current of electricity is
forced along in opposition to friction will be proportional to the amount
forced along in a certain time, i.e., to the current. And it is also evident
that the work is proportional to the force overcome; or, since this force
overcome is equal to the driving force, the work is proportional to the
driving force or electro-motive force acting. Hence, on the whole, the
heat produced in the conductor, which represents this work done, is pro-
portional to the product of the electro-motive force and current (i.e., to
E C), which is Joule's law (§ 65).
89. Connection between Conduction of Heat and of Electricity.
__It is very evident that there is some close connection between the
conduction of heat and that of electricity. For, as has been stated
(§ 46), the heat conducting and electrical conducting powers of bodies
run exactly parallel, or are exactly proportional. Moreover, substituting
temperature for potential and quantity of heat for quantity of electricity,
Ohm's law holds as accurately for heat as for electricity. Again, both
spread out from a centre in a conductor on all sides, or are of the nature
of diffusions.
Now we know that heating a body means quickening the motions of
its particles, and we see that forcing electricity through a body heats it,
or quickens the motions of its particles. This lends strong support to
the idea that electricity is transmitted by to-and-fro vibrations of the
particles of the conductor. A greater velocity of transmission will
require a higher rate of motion of the particles, and this means an
increase of temperature in the body, which is exactly what observation
shows to attend an increase of current in a conductor. This seems highly
probable as far as it goes, but must not be trusted to as anything but
a hazy approximation to a complete explanation.
90. Atomic Unit of Electricity.—We saw by Faraday's law of
electroljsis (§ 56) that if a quantity of electricity passed through an elec-
trolyte, the quantity (by weight) of an ion it took with it depended on
the atomic weight of the ion and its valency, and was proportional to the
atomic weight divided by the valency. Now, since atomic weights mean
the relative weights of the atoms, if we take weights of two substances in
proportion to their atomic weights, these quantities must contain the
same number of atoms. Hence, Faraday's law means that the passage
of a certain quantity of electricity brings the same number of atoms to
the electrodes, no matter what the substance is, except that in the case of
a divalent element only half as many are brought, in a trivalent only
ELECTRO-PHYSICS.
A-59
one-third as many, etc. This evidently amounts to saying that each
univalent atom carries a certain amount of electricity, each divalent twice
as much as a univalent one, each trivalent three times as much, etc., no
matter what the substance may be or what the weight of the atoms.
Calling the charge carried by a univalent or monad element the
atomic unit of electricity, a dyad atom carries two atomic units, a triad
three, etc. This, then, is a natural unit of electricity. An atom of a
substance is a perfectly definite mass of it, and now we see that each
atom carries a perfectly definite charge of electricity, which charge is
simply the atomic unit of electricity multiplied by the valei.cy of the
substance. •
Magnitude of the Atomic Unit.—From the roughly-known number
of atoms in a certain quantity of gaseous ion set free by a known current
of electricity we can calculate roughly the size of the atomic unit. It
turns out to be about the hundred-trillionth part of a coulomb. This is
an exceedingly small quantity, but we have to remember the smallnessof
atoms of matter and their nearness together. If we compare the electrical
attraction between them or their chemical affinity with the force with
which they would attract each other according to the ordinary law of
gravitation, we find that the electrical attraction is ten thousand million
million million times the greater 1
91. Chemical Affinity an Electrical Phenomenon.—Hence, a re-
markable parallel between the atom of matter and the atomic unit of
electricity. The atom of matter is (for the same substance) of invariable
weight, and is the smallest quantity of the substance we ever have to deal
with. The atomic unit of electricity is an invariable quantity, and is the
smallest quantity we have to deal with. Moreover, every univalent atom
of matter carries one atomic unit of electricity, every divalent atom of
matter two atoms of electricity, etc. Thus, the valency of an atom is
simply proportional to the number of atoms of electricity it carries.
The question at once suggests itself, May not the valency be caused
simply by the number of units of electricity the atom carries ?
A dyad atom (e.g., 0) attracts to itself two monad atoms (e.g., H),
giving H20. It will take neither more nor less than two. Now, a charge
of two negative atomic units of electricity on 0 would attract the unit
charges of positive electricity on two atoms of H, neither more nor less.
Thus, electrical attractions account for u chemical affinity," and there can
be but little doubt that this is the true explanation.
92. Propagation of Electro-magnetic Influence.—We have so far
been referring to what goes on in the transmission of electricity from
place to place along a conductor; but we had several instances of a cur-
rent producing effects across the dielectric surrounding the current. For
instance, a current acts on a magnet separated dielectrically from it, and
even where there is no magnet it sets up a field of magnetic force. Again,
a current induces a current in a neighboring circuit separated dielectric-
A-60
DUFF.
ally from it. So that a current exerts both electrical and magnetic in-
fluence across an intervening dielectric. These phenomena are called
electro-magnetic inductions.
Now, in § 86 we referred to the two possible views of this action: (1)
that it was direct action at a distance; (2) that it took place by an inter-
vening mechanism. We proceed, then, to show that the latter is the true
explanation,—that, in fact, electro-magnetic induction is a wave phe-
nomenon propagated through the medium in successive pulses, some-
A
Fig. 33.
what like water waves on the ocean, or sound waves in air. But for the
moment we shall offer no description of the nature of the wave. The
question simply is, Is it wave motion?
93. Interference.—One of the striking properties of waves is that
they can interfere, so as to annihilate one another at some places and
re-inforce one another in other places. Any one who has watched two
systems of water waves coming from different directions around a head-
land and meeting knows that at some places they produce a calm,
namely, where the crests of one system fill up the troughs of the other,
and at other places they produce waves of double height, namely, where
crest falls on crest. The same is true if waves are reflected
from a vertical cliff: the direct and reflected waves interfere,
producing similar effects.
To take another example, any one may, by tying an end
I of a long rubber tube to a distant wall, stretching it out, and
1 moving the end in the hand rapidly up and dowrn, produce an
interfering system of direct and reflected waves. In the
system so set up it will be observed that certain points (a)
are always at rest, and certain other parts (b) always in
motion. The former are called nodes, and the spindle-shaped
parts between the nodes are called ventral segments of the
stationarj' waves. (Fig. 33.)
A complete wave-length is twice a ventral segment in length. Now,
interference is a characteristic of all waves, and if electro-magnetic induc-
tion be a wave phenomenon it must show the same.
94. Vibrator and Resonator.—The difficulty, however, in testing
this question is how to start suitable waves, and how to detect and
measure them. In the first place, we must have something corresponding
to the hand in the above to start vibrations. This we shall call the
vibrator. Its vibrations must not be too slow, or the waves will be too
long to deal with.
B
Fig. 34.
ELECTRO-PHYSICS.
A-61
Now, if we take a pair of conductors, as in Fig. 34, and highly
charge one, it will discharge through the knobs to the other, but the
action will not stop there. Just as in the case of the oscillating dis-
charge of the Leyden jar, there will be a return rush from B to A, then
again from A to B, etc. The periods of these return oscillations will be
exceedingly short. If the plates are about sixteen inches square, the
oscillations will number thirty millions per second.
Now, how to detect the waves : here we make use of the principle
of resonance. If an organ-pipe be tuned to exactly the same pitch as a
tuning-fork, then when the tuning-fork is sounded at the
mouth of the pipe the latter will sound in sympathy.
What is called the frequency of vibration is the same in
both fork and pipe, and the pipe is said to resonate to the
fork. How can we get an instrument that will sympathize
with an electrical vibrator? The most natural would be
a plain circle of wire (Fig. 35), of such a length that the fig. 35.
currents induced alternately in opposite directions by our
vibrating primary currents would run around in the same time as the
original vibrations. What length it will need to be will depend altogether
on how rapid the vibrations of the vibrator are. With the plates men-
tioned above seven feet is a suitable circumference for the resonator.
How, finally, are we to observe the oscillations of the induced currents in
this resonator? By making a small gap in it, and noticing the currents
dashing across the gap in a spark when, after a few concurrent rushes,
they have gained sufficient volume.
Now, we are prepared to feel for the electro-magnetic waves. The
vibrator is set up vertically, a reflecting sheet of zinc set up at a distance
parallel to it. Just as in the waves reflected from the wall along the
Fig. 36.
rubber tube the electro-magnetic waves will be reflected from the zinc,
and, interfering with the direct waves, will produce stationary waves. At
the nodes of these waves the resonator shows no effect, but at the loops it
sparks. Doubling the distance between two consecutive nodes we have
the wave-length, or the distance traveled by the disturbance during one
complete vibration of the vibrator, and, multiplying by the number of
vibrations per second, we have the velocity with which the disturbance
travels.
95. Electro-magnetic Theory of Light.—The velocity thus deter-
mined turns out to be practically the same as that of light, and this is a
0
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strong confirmation of the theory otherwise almost proven, that light
waves are simply electro-magnetic waves, but of immensely smaller
length than any ordinary electro-magnetic waves. Light waves are less
than one-forty-thousandth inch in length, whereas the waves obtained as
described are several feet or even hundreds of feet long,—a difference, it is
true, immensely greater than that between the waves given by the highest
note of a piano and the lowest note, but still a difference merely of
degree, not of kind.
How could we get real light waves in such a way ? By taking a
vibrator rapid enough, e.g., a Leyden jar small enough. If we calcu-
late what the size of such a Leyden jar would be, we find its size about
the size of a molecule, which has been otherwise roughly determined.
This suggests that light waves are electro-magnetic waves excited by
electric oscillations in the molecules of incandescent matter. But it is
not necessary to imagine the atoms discharging like Leyden jars, nor yet
to imagine that the electrical oscillations are pulses of electricity rush-
ing backward and forward from end to end, as it were, of the atom, like
the oscillations of water in a trough when one end has been raised
and dropped. We know that the atoms are in vibration, their vibrations
constituting heat; and these atoms being charged, the charges vibrate to
and fro along with the atoms, and thus constitute alternating currents.
96. Maxwell's Proof of the Identity of Light and Electro-
magnetic Waves.—Though Maxwell could not measure the velocity of
such waves directly, he deduced from his theory a formula for the
velocity, in terms, of the inductive capacity of the medium and its mag-
netic permeability which, on being filled in with the values of these
constants for different media, gave practically the same number as that
which expresses the velocity of light.
His formula may be very briefly explained thus: Newton showed
that the velocity of sound waves in a medium of density (d) and elas-
ticity (e) is
Now, it will be remembered that k, the specific inductive capacity
of a medium, is proportional to the capacity of a jar, with that medium as
dielectric. This capacity is greater the greater the electric displacement
the medium allows, and this electric displacement varies inversely as the
elastic resistance to displacement; so that the specific inductive capacity
appears as the reciprocal of the elasticity. Hence, in the above formula
we write - instead of e.
K
Again, the magnetic permeability of a substance can be shown to be
analogous to the density of ordinary matter; and this magnetic perme-
ability, which is simply the ratio in which a magnetic field is strength-
ened at any point by the presence of that substance instead of air at the
ELECTRO-PHYSICS.
A-63
point, is readily determined by proper methods. It is usually denoted
by (i. Thus, the foregoing formula of Newton's becomes, for the case of
electro-magnetic waves,
Sr = \l^
V
Now, the velocity of light in various substances is deduced from their
refractive indices, and so we can test the agreement between these two
velocities. This agreement, though not perfect, is close enough to form a
convincing proof of the theory.
97. Vibrations constituting an Electro-magnetic Wave.—When
a current is started in a conductor, "a^b , it immediately sets up a field
of magnetic force, and we saw that the lines of force of this field were
circles inclosing the current (§38). Now, it is proven that this magnetic
influence of the current spreads out not instantaneously, but with a
Fig. 37.
measurable velocity, namely, that of light. We may represent this by
thinking of the circles widening out with that speed in all directions.
The circles are always perpendicular to the radial direction, such as M M.
in which they are carrying the magnetic influence of the current. Now,
this direction is the direction in which the waves travel, the front of the
wave being, of course, at right angles to the direction in which it is
traveling. Hence, the lines of magnetic force lie in the front of the
advancing waves.
Again, the growing current has an electrical influence such that,
wherever it finds a conductor, it will set up a (momentary) current in it
in a direction opposite to itself; or, at a point where it finds a dielectric,
it will set up a strain in the dielectric, the direction of the strain being
opposite to that of the original current. This direction, also, is perpen-
dicular to the direction in which the wave travels; that is, it lies in the
front of the advancing wave. But at the same time it is perpendicular
to the (circular) lines of magnetic force.
A-64
DUFF.
Now, it will be remembered that the current in the vibrator is pne
that frequently has its direction reversed. Whenever the direction is
reversed the direction of the electrical displacement at P is reversed and
likewise the direction of the magnetic induction. These are the two
vibrations that together constitute the advancing wave, viz., a vibration
of electrical displacement perpendicular to the direction of motion of the
wave, and a vibration of the direction and magnitude of the magnetic
force perpendicular to both the others.
How to picture these two vibrations and their co-existence is a diffi-
cult problem, but it may be simplified by means of the following analogy
due to Maxwell.
98. Mechanical Model illustrating Electro-magnetic Waves.—
There is the most complete proof that wherever magnetic force exists
we have something rotating about axes parallel to the direction of the
force. This proof is supplied by the rotation of the plane of polarized
light on traversing a magnetized medium
parallel to the lines of magnetic force.
Maxwell describes the field as filled with
molecular vortices rotating around the
lines of force. These rotating parts are
also elastic and compressible. Let us
think of two wheels—M and M'—of India
rubber representing two of these magnetic
vortices, with another smaller wheel be-
tween them representing a particle of electricity and tethered by springs
on either side. Suppose M set in rotation clockwise by an electro-
magnetic wave reaching it, M will then tend to turn E and E to turn M'.
But M' has inertia and will not be started all at once. Hence E in its
effort to start M' will be by the reaction pulled downward, thus stretch-
ing the upper spring. Then it gets M' into rotation in the same direction
as M's rotation. Thus we have a representation of magnetic rotation
and electrical displacement.
What happens next depends on whether the current that started this
field is a steady current or whether it is a rapidly alternating current.
If the latter, what happens is this: The rotation of M and the displace-
ment of E reach maxima, and then when the current decreases and reverses
the rotation of M ceases and reverses, thus dragging E up and gradually
setting M' also into rotation in the opposite direction. Thus, for every
reversal of the current we have a reversal of the rotation of the Ms and
a reversal of the displacement of the Es, and so the electro-magnetic
wave is propagated.
It will be noticed that the axes about which the magnetic rotations
take place are perpendicular to the plane of the paper and the direction
of the electrical displacement is up and down in the plane of the paper,
and so both are perpendicular to the direction M M' of the advancing
ELECTRO-PHYSICS.
A-65
wave or lie in the front of the wave. In this respect the model represents
the wave truly.
99. Model illustrating Induction of Currents.—Suppose this
magnetic rotation comes to a conductor, what happens then ? In a con-
ductor there is no elastic restraint of the electricity ; so a stream of elec-
trical particles is forced past by the rotating magnetic vortices, thus
giving rise to an electric current until M' has acquired the velocity of
rotation of M and then the stream stops. So there is a temporary induced
current, and it is readily seen from the model that this temporary induced
current in conductor B is opposite to the inducing current in A. Again,
at break of A the magnetic whirls between A and B gradually cease, but
those beyond B for a moment keep on, thus causing a momentarily induced
current in the opposite direction to the first one; that is, in the direction
of the current in A.
Again, if we think of A itself on first making A, there is a reaction
Fig. 39.
of the adjacent magnetic whirls to being set in motion, and this shows
itself as an electro-motive force resisting the starting of A. At break of
A the magnetic whirls keep on for a moment, thus tending to keep the
current up and causing a temporary induced electro-motive force in the
direction of the original primary current in A.
100. Function of a Conductor in the Passage of a Current.—
We have seen that when a current is started at a seat of electro-motive
force, systems of magnetic rotations and electrical displacement are
started out in all directions in the surrounding dielectric. Hence, also,
energy is being radiated. What becomes of this energy ? Part of it
passes off into space, but a comparatively small part. Most of it converges
back on the conductor that is said to convey the current. There the
strains break down and their energy is converted into heat energy. Thus,
there is a continual flow of energy into the conducting wire from the
dielectric, and so a chance given for continual new supplies of energy
being given to the dielectric. When the current does work, such as
turning a motor, it is not the energy in the conductor, but the energy of
the dielectric in the neighborhood that is transferred to the motor.
Thus, we see that the conducting wire plays the comparatively insignifi-
cant part of merely directing the flow of energy through the dielectric.
5
A-66
DUFF.
Whatever energy falls into itself is wasted as heat. The dielectric plays
the all-important part of conveying the useful energy.
From this it is apparent also that electricity is urged along through
the conductor not by pushes from behind, but by side forces, rubbings,
as it were, all along the length of the conductor.
101. Dual Nature of Electricity.—We have seen that electrical
effects are conveyed by the medium called the luminiferous ether. Is,
then, electricity simply the ether ?
Now, there are many things that strongly suggest that there are
really two electricities. In electrolysis, it will be remembered, there was
a separation of the atoms constituting the molecules of a liquid and a
procession of the electro-positive atoms down the stream toward the
cathode, and a similar procession of the electro-negative atoms up the
stream to the anode. This is a strong suggestion of a dual nature for
electricity, but it is by no means the strongest. Even in electro-statics
such a view seems called for, by the fact that electro-static strain does
not alter the volume of a dielectric, suggesting that the process consists
in the displacement of something else inward.
Again, we must regard electricity as in some sense a substance, and
therefore possessing inertia. Now, not the slightest trace of momentum
has ever been shown by a current. Again, any one who has rotated a gyro-
scope and noted the difficulty of changing the direction of its axis while
it is in strong rotation, knows what is meant by moment of momentum.
Now, the powerful currents that can be sent around an electro-magnet
should make it also difficult to turn into a new direction, unless it be that
the effect of a current in one direction is neutralized by that of a current
in the opposite direction. These and other facts suggest that there are
really two electricities.
Since, then, the ether is somehow intimately connected with elec-
tricity, and there are probably two kinds of electricity, it may be that
the two electricities co-exist in the ether in somewhat the same way as
hydrogen and oxygen exist together in water. When one goes in one
direction the other goes in the other direction, like the procession of the
ions in the electrolysis of a liquid. In a dielectric there is difficulty
in separating the components, and even when separated a short distance
they will spring back, thus giving the dielectric the elastic property to
which we have several times made reference. If too far separated they
do not return, but fly apart, causing what we call a disruptive discharge.
Again, in a conductor, the bonds connecting the two constituents are
somehow relaxed, so that they are readily separated. This, however, is
merely a guess quite unverified, but looking very plausible.
ANIMAL ELECTRICITY.
By WESLEY MILLS. M.A., M.D., L.R.C.P.Lond., F.R.S.Can , etc,
MONTREAL, CANADA.
Animal electricity is a subject as wide as it is inviting. Electric
phenomena have been demonstrated in connection with the development
of the embryo, with the secretory processes of glands, with the heart-
beat, etc. In fact, the subject has been sufficiently developed to warrant
the surmise that all vital phenomena may have electric as they have
chemical concomitants ; though such is yet far from proven. The elec-
tricity of muscles and nerves has been investigated with great thorough-
ness, and will be found treated in another part of this work. When it
was discovered that certain fishes possessed electric organs, these
naturally became the subjects of investigation b}T some of the leaders in
physics, as Faraday ; and of electro-physiologists, including that great
master and, in fact, discoverer of what is most important in the electricity
of muscles and nerves, Prof. E. du Bois-Re3'mond.
His researches, together with the later ones of Professors Burdon-
Sanderson, Gotcli, and Ewart in Great Britain, make up the most valu-
able part of what has been achieved in this direction up to date. Were
the space at our disposal for this subject not so limited it might be
interesting to glance at the labors of others, imperfect as they are; but,
under the circumstances, it will probably be wiser to attempt to la}'
before the reader, in the briefest way, an account of the methods and
results of those investigators only who have most advanced the subject,
and whose previous researches in kindred fields have won our con-
fidence.
The principal-known electric fishes are the Gymnotus, or electric
eel; the Malapterurus, or sheath-fish ; the Torpedo, and several other
species of rays.
The Gymnotus electricus is the most powerful of all known electric
fishes, and may attain a length of five or six feet. It frequents the
marshes of Brazil and the Guianas, and its shocks are capable of stunning,
if not actually killing, the largest animals. Humboldt informs us that
the direction of certain roads had to be changed in consequence of the
numbers of horses annually killed as they passed through the ponds
which these fish inhabited. Its electric organs consist of two pairs of
long structures situated immediately beneath the skin,—one pair on the
back of the tail and the other along the anal fin. The organ is made up,
as is usual, of cells filled with a sort of gelatinous material, and in this
creature are so small that two hundred and forty have been counted in
(A-67)
A-68
MILLS.
the space of one inch. It is estimated that about two hundred nerves
are supplied to the whole apparatus, these being derived from the anterior
branches of the spinal nerves, and, as applies to the nerves of all electric
fishes, are larger than those supplied to other parts. It is clear that an
animal capable of giving such powerful shocks is not as well adapted for
nice experiments as less-powerful fishes.
Fig. 1.—The Electric Fish Torpedo, Dissected to Show Electric Apparatus.
(Huxley.)
b, branchiae; c, brain; e, electric organ; g, cranium ; 7?ie, spinal cord; n, nerves to pectoral fins;
nl, nervi laterales; np, branches of pneumogastric nerves to electric organs; o, eye.
I. Following the historical development of the subject, we proceed
to give some account of the important researches of Prof. Emil du Bois-
Reymond on the tropical sheath-fish, the malapteriirus. This fish is
found in the rivers of Africa, including the Nile, specimens occasionally
ANIMAL ELECTRICITY.
A-69
reaching a length of four feet. The electric organ extends over the
greater part of the body, lying beneath aponeurotic membranes under
the skin. The cells making up the organ are rhomboidal and filled with
a somewhat firm jelly. The nerve-supply consists of a single strong
fibre, which gives off branches to different parts of the organ. The minute
structure of electric organs will be described and illustrated later. A
general idea of an electric fish may be obtained from Fig. 1.
Professor Goodsir, of Edinburgh, supplied Professor du Bois-Rey-
mond with the specimens he first used for experimentation. The}- were
kept in a trough constructed with a view of preserving a constant supply
of fresh, well-aerated water of a suitable temperature, and were fed at
first on earth-worms and later on strips of beef. The specimens were
small, without barbels, young, and mostly females. The color of the fish
varied with the degree of exposure to light. In darkness they became
blackish, and when fatigued by experiments pale, returning to their
former color after resting for a few days. They became more lively at
Fig. 2.
night; in fact, showed fear of light. When other fish were put in the
same tank with them they immediately discharged their electric organs
successive^, the victims soon drifting about apparently lifeless. When
left in the tank such fishes died, but if withdrawn they recovered. A
frog under similar circumstances stretches out as if stiwchnized. In
bad health the electric power was correspondingly diminished.
Method of Experiment.—The malapteriirus being a fresh-water fish,
not large, tenacious of life, and the electric organs supplied by a single
large nerve originating in a giant ganglion-cell, is much more easily
investigated in many respects than some others. Fig. 2 will give an
idea of the fish, the apparatus used, etc. It will be observed that the
animal is almost entirely covered with a gutta-percha case having linings
of tin-foil at the two extremities, indicated by the dotted lines. These
communicate by means of strips of tin-foil (k s) covered by insulating
A-70
MILLS.
material, with the handle where they are soldered to small copper plates,
in which the wires end. a a' denote the surface of the water in the
tank. The arrows indicate the direction of the currents.
Another ingenious and much-
used apparatus is that shown in
Fig. 3, illustrating the " frog-
alarum" and " frog-interrupter,"
which in great measure explains
itself. By means of the "frog-
alarum " it was always possible
to learn when the fish being ex-
perimented on gave a shock, and
by the " frog-interrupter" only
one shock was allowed to pass
through the galvanometer, no
matter how many were given.
We may now deal briefly with the
results of the experiments :—
Subjective Test.—By touch-
ing the head and back of the fish,
or seizing it between the wetted
hands, shocks varying in intensity,
but powerful for the size of the
animal, may be perceived.
Direction of the Shock.—As
shown fry the arrow in Fig 2, the
current passes from the head
toward the tail, i.e., in a direction
opposite to that of the shock of
the gymnotus.
Physical Investigation of the
Shock. — The principal results
were : Polarization of electrodes,
but no distinct electrolysis of
water resulted. Passage of a
spark was observed^ by the use of
a special apparatus. Induction,
magnetization of soft iron, and
electric attraction were all dem-
onstrated.
Tensions.—The poles of the
organ lie at the head and the tail,
and the posterior half of the organ acts more feebly than the anterior,
owing to greater resistance in the former.
Relative Immunity from Electric Shocks.—Both Humboldt and
Fig. 3.
E and Ef. zinc electrodes in the trough containing
the fish; F, H, Glr the bell, hammer, and muscle ar-
ranged to form an alarum: a, p, q, lever of the frog-
interrupter; ffn, its muscle; p. the platinum point
which rests upon the supporting plate ; q, amalgamated
copper wire which dips into mercury: k, A'/, keys; B,
galvanometer. The action of the interrupter is such
that only one shock can pass through the galvanometer,
for by the contraction of the muscle Gn the galva-
nometer circuit is broken at q and not again closed.
The alarum, of course, goes on ringing.
ANIMAL ELECTRICITY.
A-71
Collodon had expressed the opinion that electric fishes do not shock
each other when their batteries are discharged, and du Bois Reymond's
experiments proved that the malapteriirus is not affected by currents
from a battery that suffice to kill other fish. The torpedo is viviparous,
yet its young are not killed in utero by its own discharges. It appears,
then, that electric fishes can withstand both their own and outside shocks ;
and although du Bois-Reymond discussed the reasons of this immunity,
he did not satisfy his own mind on the subject. Of course, such fishes
are not absolutely unaffected, and could, no doubt, be killed by a very
powerful electric discharge.
The Isolated Living Electric Nerve and Organ.—It will suffice to
note that such a nerve acts like any other nerve under similar circum-
stances,—e.g., when laid on the organ of the same side and tetanized, a
nerve-muscle preparation responded by tetanic contractions. Like
muscle, fresh electric organ is neutral, becoming acid on standing; but
when kept in warm water a short time it becomes acid, in this respect
resembling the central nervous system.
II. We shall now proceed to state the results of the same physiolo-
gist's researches on the Torpedo electricus.
Prof, du Bois-Reymond first used for experiments specimens kept
in the Berlin Aquarium which were brought from Trieste, and these were
succeeded by others of a more definite character made upon fish supplied
through the aquarium at Trieste. The animals used belonged to the
species Torpedo marmorata, and were between twenty-five and thirty-six
centimetres in length. They were kept in tanks in the Berlin Aquarium,
burrowing in the gravel at the bottom and apparently unconcerned as
to the presence of other fishes. When unconfined they eat fish of con-
siderable size, which they first paralyze by their shocks; however, in
confinement they do not seem to have taken the cut-up fish thrown into
the tanks. When experiments were about to be performed they were re-
moved from the tanks by means of a landing-net to a tub, and thence
transferred to the experimental trough described below, and illustrated
in Fig. 4.
The arrangement shown assumes that a shock is to be imparted to
a human being ; so that there are two handles in the experimental circuit,
to one of which, Hv, the wire v' is conducted. The fish represented
in cross-section is lying in a glass vessel thirty centimetres wide and
ten centimetres deep, on the bottom of which there is a circular zinc
plate of about the same width as the body of the animal, forming a ven-
tral shield v v°, a portion of which, v v', was bent and hung hook-like
over the side of the vessel. One end of the experimental circuit was
brought into contact with this hook; a circular piece of flannel,//', soaked
in sea-water, was laid on the ventral shield to prevent the edge of the
dorsal shield d d° from touching the ventral. The specimen rests on the
A-72
MILLS.
flannel. The dorsal shield is an arched zinc plate with the edge turned
up, the upper surface of which is lacquered and provided with a wooden
knob in the middle, through which the leading-off wire, d' Hd, is con-
ducted, insulated, to the second handle. There was just enough sea-water
in the receptacle to cover the back of the fish, and no more. It will be
noticed that there is a frog-alarum in the circuit, the arrows, as usual,
showing the direction of the current; G is the gastrocnemius, with its
nerve; T the bell, .ETthe hammer, and E the weight.
Subjective Tests.—By means of this apparatus (Fig. 4) du Bois-
Reymond succeeded in giving a shock to the students in attendance at
Fig. 4.
his lectures, who joined hands, after wetting them. Of course, the
strength of the shock varies with the condition and size of the specimen.
As a matter of fact, torpedoes seem to lose the power of giving vigorous
shocks sooner in confinement than does the malapterurus.
Electrolysis of Iodide of Potassium.—By means of a special form of
electrol}rzer this physiologist, like Davy and Matteucci, got this salt
decomposed, and, in addition, there appeared a spot at the primarily
negative pole, owing to polarization in consequence of the electrolysis ;
so that there is a secondary current in the opposite direction to the
primary, explaining the change in pole.
The Organ Current.—By this is meant, as opposed to the shock, a
ANIMAL ELECTRICITY.
A-73
current persistentl}' generated through the electric organ, and usually in
the direction of the shock. This organ current has been observed by others
in the torpedo, in the skate, and in the gymnotus. Du Bois-Reymond
found by the galvanometer that this current varied with the organ of the
animal, and he made several measurements of its strength. According to
Sachs, tetanus of the electric organ in the gymnotus weakens the current.
Secondary Electro-motive Actions of the Organ of the Torpedo and
Irreciprocal Conduction.—By means of apparatus used to investigate allied
phenomena in muscle and nerve du Bois-Reymond established some very
interesting conclusions, which, however, may be stated briefly : " Internal
polarization of the organ follows the passing of a current through it in
the direction of the columns, which, like the polarization of muscles,
nerves, and the organ of the malapteriirus, is, under different circum-
stances, sometimes relatively positive, sometimes relatively negative, the
conditions required for the appearance of both polarizations being gener-
ally the same in the latter as in the former.". Different results were
obtained, according to the direction of the current sent through the
organ. This difference of strength of current must depend on either
unequal electro-motive strength or unequal resistance. By " irreciprocal
resistance " is meant that conduction may be better in the direction of
the shock than in the opposite direction, and du Bois-Reymond was led
to believe in its existence in the torpedo.
Electro-motive Actions of Electric Nerves in the Torpedo.—The eight
electric nerves of this creature,—four on each side,—which can be pre-
pared, without branches, of a length of three to four centimetres, and of
an averao-e thickness of two and a half millimetres, served admirably for
the investigation of this subject. This part of the investigation was
carried out by Professor Christiani, who found that the greatest electro-
motive force obtained was more than twice as small as that of the nerves
of the froo- more than three times as small as that of the nerves of birds
or of mammals, excepting the horse, and over five times as small as that
of the nerves of the lobster. One peculiarity Prof, du Bois-Reymond
discovered himself, viz., that the peripheral transverse section shows
greater negativity as regards the equator; though it seems probable that
this is not, strictly speaking, a peculiarity of electric nerves.
Negative Variations of the Current of the Electric Nerves when in
a State of Activity.—Carefully-conducted experiments established the
negative variation, though there were associated phenomena difficult to
explain.
Prof, du Bois-Reymond's Second Investigation of
Living Torpedoes.
This confirmed some previous results and developed new ones, which
we proceed to give.
Electro-motive Behavior of the Skin of Electric Fishes.—Employing
A-74
MILLS.
the usual methods of investigation of such phenomena, it was con-
cluded that the skin of the torpedo behaves electro-motively like that
of the gymnotus, in regard to the direction as well as the magnitude of
the action, and like that of the malapterurus in direction, and in all three
fishes the force is probably about equal.
Irreciprocal Conduction.—This apparent irreciprocity of conduction
was shown to increase with the current density, to have its seat in every
transverse lamella of the preparation, and to increase with the length of
the columnar track which is traversed by the current.
Resistance of the Electric Organ.—The main conclusion is that the
organ conducts best in the direction of the shock, but even in that case
scarcel}' half as well as frog-muscle parallel to the fibres, and from seven
and one-half to twelve times worse than the sea-water of the aquarium,
and much worse still than sea-water of the Mediterranean ; but in the
opposite direction to the shock, from twenty to fifty-eight times worse
than sea-water.
Further investigation showed that these differences are dependent
on the vitality of the organ, for as this diminishes a condition of equality
in conduction—i.e., resistance—is approached. The advantage, to the
fish, of this state of things is obvious ; at all events, so far as the direc-
tion of least resistance is concerned, and on the principles of organic
evolution, it is possible to understand why development should take place,
as it usually does, in those ways, and those only, which are advantageous
to the individual.
Researches of Professors Burdon-Sanderson and Gotch.
It is proposed now to give an account of the researches more
especially of Professors Burdon-Sanderson and Gotch, with incidental
reference to the work of some other investigators, including that of Pro-
fessor Ewart, in the development of electric organs. These are detailed
in two papers in the Journal of Physiology, vol. ix, Nos. 2 and 3, and vol.
x, No. 4. in which researches the skate was the fish employed, the work
being done in July, 1887, at the marine laboratory at St. Andrews.
FIRST RESEARCH.
Previous Anatomical Researches of Stark, Robin, and Max Schultze.
—These are summarized in the paper of Sanderson and Gotch, from
which the present writer extracts. Stark discovered the electric organ
of the skate in 1844. Robin made a communication to the Academy of
Sciences on the same subject in 1846, and at greater length in 1865.
He describes the organ as consisting, in large skates (seventy centi-
metres wide), of a spindle-shaped structure fifty centimetres in length,
which is placed on either side of the vertebral column of the tail. It is
gray in color and semi-transparent, and is traversed transversely and Ion-
ANIMAL ELECTRICITY.
A-75
gitudinally by septa, which divide it into compartments, of which the form
is that of a lozenge. The cephalic proximal end of each organ is sheathed
in concentric layers of muscle. Bj- its median face it is in relation with
the dorsal and ventral spinal muscles, but between these there is a space
along which it touches the vertebral column, and here the blood-vessels
and nerves enter it. The rounded external part of the surface is subcu-
taneous. The blood-supply of the organ is derived from the intervertebral
branches of the caudal arteiy ; the veins join corresponding branches of
the subcaudal vein. The arteries find their way by means of longitudinal
septa to the discs, to be immediately referred to. The nerves are derived
partly from the anterior roots of the nearest spinal nerves, partly from
the trunks of those nerves beyond the junction, and are distributed in a
manner similar to the arteries until they approach the discs, where their
mode of termination will be described later.
M. Robin's description of the minute structure of the organ is as
follows : He regards the discs already mentioned as its essential elements.
These, which are polygonal in contour and about three millimetres
wide, are separated from each other hy transverse septa. The anterior
surface of each of the discs is smooth, the posterior alveolated. They
are arranged in piles (columns), which are separated from one another
by longitudinal septa, and which vary in number according to the
species of the animal. The space between the alveolated surface of a
disc and the smooth surface of the one behind it is entirely occupied by
connective tissue containing and supporting blood-vessels and nerves, all
of which go to form what M. Robin calls the " cloison." Each arteriole
as it enters the cloison from the longitudinal septum divides into capillary
branches, all of which tend forward and terminate in loops, which oceup}'
the alveoli on the posterior face of each disc. The nerves, which enter
the cloison in the same way as the arteries, at once separate from them
by dividing into branches, which tend backward, to be distributed to the
smooth surface of each disc. It thus appears that each disc receives its
blood-supply from behind, and its nerve-supply from the front; and the
separation of nerves and blood-vessels is so complete that, while in the
connective tissue filling the alveoli there are no nerves, in the rich plexus
"of nerves covering the anterior smooth surface there are no capillaries.
The substance of the disc is, according to Robin, not entered either by
capillaries or nerves, and consequently their terminations never come
nearer to each other than the distance between the deepest alveoli and the
smooth anterior surface of the disc (one-fifth millimetre). The medul-
lated nerves he describes as forming a plexus over the anterior surface
of the discs. Each medullated fibre ends by branching into two, three,
or even four filaments, and these again divide, at the same time losing
their medullary sheaths, and finally their nucleated sheaths, after which
they are continued as axis-cjdinders. Many of these terminal branches
are connected close to the surface of the disc with " nucleated multipolar
A-76
MILLS.
cells of irregular form." From these cells fibrils two-one-thousandths to
three-one-thousandths of a millimetre in diameter tend toward the surface
of the disc, dividing repeatedly, so that in longitudinal sections of the
organ these nervous terminations present an appearance described by
Robin as resembling bunches of root-hairs (chevelu radiculaire extreme
ment riche). On arriving at the surface of the disc each fibre terminates
in a pyramidal or conical body, from four to five thousandths of a milli-
metre in length, the base of which is applied to the disc. The plexus of
nerves, with its terminations, separates very easily from the disc, and pre-
sents in surface-view a finely-granulated appearance, with minute per-
forations here and there, the granules representing the terminal pyramids.
On focusing below the surface, the field appears to be beset with minute
points, which are the optical sections of the terminal fibres.
The description, of which a summary has just been given, we find to
be correct as regards almost all the points to which it relates. The only
statements which we are disposed to question are, first, the description
of compartments, which are not lozenge-shaped, but, as a rule, oblong
and rectangular in section, and, second, those which relate to the multi-
polar cells in the nervous plexus and to the pyramidal bodies in which
M. Robin believed that the nerve-fibrils terminated. To these points we
shall recur in giving an account of our own observations upon the struct-
ure of the organ.
The minute structure of the electric organ was investigated in
Raia clavata, by Prof. Max Schultze,in 1858. His attention was directed
almost exclusively to the mode of termination of the nerves. He con-
siders that the disc, the structure of which he minutely describes, owes
its existence to a coalescence (verschmeltzung) of the terminations of
the nerves, of which its intercellular substance is a direct continuation
He describes the nerve-endings as constituting a fine net-work, which in
the disc is transformed into a solid nervous mass, part of which can be
split into laminae, the remainder consisting of finely-granular substance
inclosing nucleated cells. The chief foundation for this view of the
morphological import of the disc seems to be a peculiar microchemical
reaction common to the disc and nerves. Both are colored red by sul-
phuric acid and sugar.
M. Robin's experiments on the electric properties of the organ are
of importance only in so far as they afforded for the first time experi-
mental proof that its function is in accordance with its structure. It
had previously been designated by du Bois-Reymond as " pseudo-elec-
tric," but in consideration of Robin's investigation he now proposes
to distinguish it from the electric organs of the torpedo, gymnotus, etc.,
by the term " incomplete" (unvollkommen). It is, however, difficult to see
that the new word is better fitted than the old one to express its char-
acter, for the organ, though small, is as perfect in structure and function
as that of the gymnotus or the torpedo.
ANIMAL ELECTRICITY. A-77
Histological Observations Made by Professors Sanderson and Gotch.
—The relations of the electric organ to surrounding parts can be best
understood from the engraving (Fig. 5), which represents in outline a
transverse section of the tail, where it occupies most space. It is seen
that its surface is mapped out into polygonal areas by the cut edges of
the longitudinal septa, and that these radiate more or less distinctly from
the obtuse angle on the median side of the section, which corresponds to
the line of attachment along which the vessels and nerves enter. It is
also noticeable that the external areas are arranged concentrically around
the central ones.
Fig. 5.—Transverse Section of Tail of Large Skate (Raia batis).
Actual size.
sp.c, spinal canal; i>, vascular canal containing caudal artery and vein; m, muscles ; o, electric organ.
In Fig. 6 the engraver has given the general effect of a photograph
of a longitudinal frontal section, as seen under the microscope with a low
power. It serves to show that the organ consists of spindle-shaped tubes,
imperfectly divided into loculi placed one above the other, and each
holding a disc. These tubes are so arranged that their axes are either
parallel or very slightly diverge backward. The discs are, so to speak,
suspended by the connective tissue which supports the blood-vessels. As
has already been stated, the arterioles follow, in the first instance, the
longitudinal septa by which the tubes are separated from each other.
From the septa terminal arterioles pass transversely—i.e., at right angles
to the axis of each tube—into the spaces between each two adjoining
discs, occupying a position about half-way between their two opposed
surfaces. The description of their distribution, which we have given
from M. Robin's memoir, need not be repeated. Both arteries and veins
are accompanied by connective tissue, which in the horizontal part of
their course is of sufficient strength to deserve the name of a lamina,
although it is distinguished from the rest of the connective tissue, which
occupies the space between the discs merely by the closer arrangement
of its fibres.
On the caudal side of each of these laminae of connective tissue and
blood-vessels, and consequently between it and the disc behind it, there
A-78
MILLS.
exists a plexus of medullated nerves-; the relations and mode of termina-
tion of which can be best seen in sections of the frozen, perfectly-fresh
organ, which, after having been first placed in normal salt solution, are
treated on a slide with 1-per-cent. solution of warm osmic acid. In such
sections what we propose to call the nervous lamina is seen to be
attached to the nucleated membrane which covers the anterior surface
of the disc by a well-defined border. The terminal fibres which end
abruptly at this border can usually be traced back to a bifurcation of the
characteristic form shown, and the nerve-fibre from which the two prongs
spring to a medullated nerve in the plexus already referred to. We are
not able to confirm M. Robin's notion as to the nervous nature of the
Fig. 6.—Longitudinal Section of Upper Part of Organ as Seen under
Low Power (Raia batis). The arrow indicates the direction of the shock.
branched (or multipolar) cells, which are in relation with the terminal
ramifications of the nerves. Some of these cells unquestionably belong
to the nucleated sheaths of the nerve-fibres ; others are probably con-
nective-tissue elements. As to the mode of ending of the ultimate fibrils
we are uncertain. In sections of the organ hardened in chromic acid the
border of the nervous lamina exhibits a beaded appearance of'very great
regularity, and it can be seen that each of these beads has a terminal
fibril leading to it; but no such structure can be made out in osmic-acid
preparations. Whether this appearance means that the minute terminal
fibrils end in the way described by M. Robin, or give off even finer
branches, we are unable to state. All that we have been able to ob-
serve with certainty is that they can be traced up to, but not beyond,
ANIMAL ELECTRICITY.
A-79
the surface of the disc, and that their direction is perpendicular to its
surface.
The morphological meaning of the structure described in the preced-
ing paragraphs can only be understood by referring to its development,
which has been lately made the subject of study by Professor Ewart. It
is sufficient to sa}r that, although each disc occupies the place of an undi-
vided muscular fibre, it belongs histologically to the nervous system, not
to the muscular. It is, in short, sui generis, and cannot be identified
with anything excepting the organs of similar function found in other
fish. That in several important particulars it resembles a muscular
Transverse septum.
Medullated fibres of the plexus, "1
I Nervous
j lamina.
Terminal ramification of non-medul- [
lated nerves, J
Nucleated lamina,
Striated lamina,
- The disc.
Alveolated lamina, .
Connective tissue.
Transverse septum. At its junction with the
longitudinal septum a nerve is seen in section.
Fig. 7.
nerve-ending or muscle-plate cannot be questioned. Just as the ramifi-
cations of the nerve terminate in the end-plate without being part of it,
so the myriad fibres of the nerve-lamina end in the nucleated layer which
in the adult organ, but much more strikingly in earlier stages of its
development, corresponds in structure with the granular nucleated sub-
stance. Physiologically the two correspond; for just as at the instant
that a muscular nerve is excited the end-plates become positive to the
nerve itself, so here excitation of an electric organ determines an
instantaneous change in the same direction at the surface of every disc.
But these considerations do not afford sufficient ground for any conclu-
A-80 MILLS.
sion as to the analogy between the " electric plate " and the " motor
end-plate." On this point we would defer expressing an opinion until
we have the opportunity of acquiring more exact information than we as
yet possess as to certain of the pl^siological relations of the former, and
particularly the influence of curare, since it is well known that in the
case of the torpedo the electric organ is not affected by that poison,
even though all the muscular nerve-endings are completely paralyzed.
Method of Experiment.—The skate was secured with its ventral
surface downward on a board shaped like a racquet, the tail projecting
along the narrow handle. The board was then plunged in a tub of sea-
water, the tail being left exposed. The apparatus used to give, indicate,
and record electric currents were the same as those usually employed in
muscle-nerve physiology, including the capillary electrometer.
As a result of their experiments, Professors Burdon-Sanderson
and Gotch draw the following conclusions, which are in harmony with
experiments made on the torpedo :—
Conclusions.—1. In Raia batis and clavata an electric organ exists
which corresponds in structure and function with other electric organs
in fishes. It possesses the fundamental endowment by which electric
organs are distinguished from other electro-motive and excitable struct-
ures, namely, that its electro-motive elements are arranged in series
after the manner of a voltaic pile, so that the effects of excitation
increase proportionally to the number of elements in series which are
brought into action. The maximum electro-motive force of the shock—
i.e., the electro-motive force corresponding to one centimetre length of
organ—we have roughly estimated to be about half a volt. In the tor-
pedo it is probably ten times as much. 2. The natural discharge or
shock of the electric organ consists of a succession of electric dis-
turbances, in each of which the distal (caudal) end becomes positive to
the proximal (cephalic) end. 3. A similar discharge can be evoked by
exciting the spinal cord by a single induction shock, provided that the
part excited is at some distance from the organ. 4. Similar excitation
of the part of the cord from which the organ receives its nerves is fol-
lowed at an interval of about a hundredth of a second by an " excitatory-
response" of extremely short duration (two- to three- hundredths of a
second) ; this effect, of which the direction is always normal, must be
regarded as analogous to the excitatory variation of a nerve when sub-
jected to a single instantaneous excitation. 5. The passage of an
induction shock through the prepared organ is followed, after an interval
of about five-thousandths of a second, by a similar •' excitatory response,"
the direction of which is always normal, whatever may be the direction
of the exciting induction current. 6. The excitatory state is not propa-
gated in the electric organ, but is limited to the part to which the
excited nerves are distributed, whether the seat of excitation be the
spinal cord or the organ itself. 7. In the uninjured organ there may or
ANIMAL ELECTRICITY.
A-81
may not be a difference of potential between the cutaneous surfaces
covering the upper and lower ends of the organ respectively. If a dif-
ference exist it is usually in the normal direction, i.e., the distal end is
positive to the proximal. In the prepared organ such a difference almost
always exists, and this is suddenly augmented, if present, or brought
into existence, if absent, by anjr injur j' of the surface of the organ, and
more particular!}' by momentary exposure of it to a high temperature.
The effect so produced rapidly subsides, but a residue of it remains, and
may last for some time. 8. When the organ is divided transversely the
injured end is not thereby rendered negative to the uninjured. 9. When
an induction current of sufficient strength is led through the organ it
produces, in addition to the excitatory response, an after-effect which
resembles, both in its constant normal direction and in its time relations,
the effect produced by injury, but is of relatively small electro-motive
force. It is produced by currents in either direction, but is stronger
when the direction of the induction current is normal. 10. A similar
excitatory after-effect, accompanied by polarization, follows the passage
of a voltaic current of sufficient strength and suitable duration. 11. A
similar after-effect follows the natural shock as well as the " excitatory
response." We understand this to mean that just as by the action of an
external current the organ is brought into a state of sub-excitation,
manifesting itself in a temporary increase of the normal difference of
potential between its ends, so the current of the shock or of the excita-
tory response produces a similar sub-excitation. There, as in the skate,
we have a normal discharge of central origin ; an " excitatory response "
due to excitation of the nerves of the electric organ; an " organ-
current " capable of being brought into existence or augmented by
injurv of the surface; after-effects, physiological or merely physical, i.e.,
due to polarization ; and, finally, all physiological electro-motive effects,
whether they come under the designation of shock, of excitatory re-
sponse, of organ-current, or of after-effect, in one and the same normal
direction.
SECOND RESEARCH.
A second investigation was undertaken by the same physiologists,
with a view of answering certain questions, more especially in regard to
the normal reflex process by which the electric organ is discharged,
and the measurement of the electro-motive force of the response of the
oro-an to a single excitation. The results of this research will be found
in the following summary of the investigators themselves :—
Conclusions.—1. Spontaneous discharge of the electric organ of
the skate has not, so far as we know, been observed. A reflex discharge
can alwavs be induced by mechanical stimulation of the skin, particularly
that of the dorsal surface. 2. The afferent paths by which the reflex is
excited are contained, for the most part, in the spinal nerves. Although
6
A-82
MILLS.
discharges follow electric excitation of certain branches of the trigem-
inus, they can be evoked reflexly after all the cranial nerves have been
divided. 3. The reflex discharge is always discontinuous,—i.e., it consists
of a group of two or more single electric effects, which follow each other
with a frequency of from eight to twenty-five per second. If the stimu-
lation is prolonged, this primary group may be succeeded by others of a
similar character. 4. A reflex centre is situated in the optic lobes.
Electric stimulation of the dorsal surface of these lobes produces while
it lasts a discontinuous discharge of the same character as the primary
reflex discharge. 5. The discharge goes on after the excitation has
ceased, manifesting itself either by prolongation of the primary effect or
by the recurrence at intervals of secondary effects similar to the primary.
6. Electric stimulation of the anterior region of the cord after it has
been separated from the bulb also evokes a discontinuous discharge, which
lasts as long as the excitation. It is followed by effects of the same kind
as those which follow excitation of the optic lobes, but these are less
intense and of less duration. This part of the cord must therefore be
capable of automatic action, although there is no evidence that it can be
excited reflexly. 7. Each disc of the electric organ is capable of
developing, during the state of excitation evoked by a single induction
shock, an electro-motive force of over 0.02 Daniell. The sartorius muscle
of the frog (as we have found in our own experiments) is capable, when
excited by a single induction shock led through its nerve, of developing
an electro-motive force of 0.026 Daniell. The number of nerve-fibres
distributed to the disc is certainly not less than that of the constituent
fibres of the nerve of the sartorius. There is therefore no reason to
reo-ard the electric activity of a disc as extraordinary as compared with
a muscle of similar innervation.
The relatively large electro-motive force which the organ as a whole
is able to develop is attributable (1) to the large number of discs of
which it consists, (2) to their being arranged in pile, and (3) to the
nervous arrangements by virtue of which they are enabled to act simul-
taneously.
Addendum.—Since the foregoing pages passed into the printer's
hands a most interesting paper on the origin of the electric nerves of
the torpedo, gymnotus, mormyrus, and malapterurus, by Professor
Gustav Fritsch, of Berlin, has appeared in Nature, vol. xlvii, No. 12.
The reader who is especially interested in this part of the subject will
do well to refer to this paper, which is admirably illustrated by photo-
oraphs from nature.
The writer gives here a brief outline of the paper, without com-
ment :—
Electric organs are of muscular origin. This* is well seen in a cross-
section of the tail of the mormyrus, in which instead of muscles one
ANIMAL ELECTRICITY.
A-83
finds electric tissue, only the longitudinal tendons passing outside the
electric organs from muscles placed anterior!}'. Again, in the electric
eel (Gymnotus electricus) of America a similar section shows that a part
of the muscle-tissue is changed into electric organs, the rest remaining
unchanged. In the electric skates the electric organs are developed from
muscles that originally belong to the branchial arches and the arch of the
lower jaw. In all cases in electric fishes the impulses that pass along the
nerves and call forth the electric discharge proceed from ganglion-cells.
In the torpedo the ganglion-cells are collected in a bean-shaped mass in
the medulla, forming an electric lobe, and estimated at about fifty-four
thousand. In connection with these an equal number of nerve-fibres
have been found. In the electric eel the electric cells form a continuous
column in the spinal cord,—long and slender, and amounting probably
to sixty thousand. The arrangement in the mormyrus is similar. The
protoplasmic processes of the cells must have a conducting function, a
remark which applies probably also to all ganglion-cells. In the electric
fish of the Nile (Malapterurus electricus) muscular tissue is abundant
and the electric organ seems to have been developed from the skin.
In these the electric current passes through the body in a direction
opposite to that in other electric fishes. The innumerable nerve-branches
are all derived from two electric nerve-fibres, the structure of which is
very suggestive of an electric cable, and leading inward each to a single
ganglion-cell. This is of great size, having no real axis-cylinder arising
from it, but, in place of it, branched protoplasmic processes join and
form a kind of perforated plate beneath the cell, from which the nerve-
fibre starts. Since it is clear that ganglion-cells are the real centres
concerned in all kinds of electric fishes, it seems reasonable to believe
that in other animals they are not merely trophic, but distinctly motor.
The great value of such investigations as these is owing to the light they
throw on nervous processes generally, and on the remarkable develop-
ment effected by organic evolution.
BIBLIOGRAPHY.
Instead of enumerating all the original sources of information in this article, the
reader is referred to " Biological Memoirs," edited by Professor Burdon-Sanderson, and
to the Journal of Physiology, vols, ix and x, in which will be found a very elaborate list
of references.
STATIC ELECTRICITY AND MAGNETISM.
By HENRY McCLURE, M.D.,
CROMER, ENGLAND.
The state of transition through which electrical science is at present
passing renders it difficult to treat the subject with that degree of lucidity
which the logical mind demands. With the phraseology and, to a certain
extent, the conceptions of the older theories, we are gradually rising to
generalizations which tend more and more to give a new meaning to all
electrical phenomena. That meaning is not yet clear enough, however,
to enable us to put aside the older views and to start afresh with new
terms and new definitions. We have still to accommodate ourselves to
the imperfections of a transitional indefiniteness, and to employ language
which the passing months are rendering obsolete. As long, however, as
we endeavor to import into the older phraseology a meaning more in
keeping with the results of modern discoveries, we cannot go far astray.
We may still, for instance, use Franklin's, or the dual theory of elec-
tricity, if we apply to them the corrections furnished by modern science.
The chief exponent of these modern views is Prof. Oliver Lodge, whose
treatment of the subject will occupy our attention in the earlier pages,
and will, I hope, be the means of placing the phenomena of electro-statics
in a somewhat clearer light.
The ethereal theory of electricity presupposes the existence of a
perfectly subtle, continuous, incompressible substance pervading all
space and penetrating between the molecules of all ordinary matter
which are imbedded in it and connected to one another by its means ;
and we must regard it as the one universal medium by which all actions
between bodies are carried on. This, then, is its function : " To act as
the transmitter of motion and energy." We have long known this sub-
stance or fluid as the ether, and to its vibrations we are indebted for the
light of our planet. Professor Hertz, of Bonn, has conclusively shown
that these vibrations are electrical vibrations, but electrical vibrations
by reason of their short wave-length appealing to a sense-organ which
we possess. We have no sense-organ for ordinary electrical waves ; their
length is such that the retina cannot take them up. Professor Hertz
has, howrever, by a stroke of genius, made these electrical vibrations
visible to us by simply shortening their wave-length, and has shown,
moreover, that they obey all the laws of optics,—can be reflected, re-
fracted, etc., and that they travel at exactly the same rate that light
travels.
So electricity has annexed the whole domain of optics. Now, vibra-
tions of light which we know the ether transmits must be transmitted by
(A-84)
STATIC ELECTRICITY AND MAGNETISM. A-85
something possessing rigidity ; rigidity means active resistance to shear-
ing stress, i.e., to alteration in shape ; it is called elasticity of figure. It
is by the possession of rigidity that a solid differs from a fluid. For a
body to transmit vibrations at all it must possess inertia. (Inertia is
defined as ratio of force to acceleration. Transverse vibrations can only
be transmitted by a body possessing rigidity ; all matter possesses inertia,
but fluids only possess volume elasticity, and, accordingly, can only
transmit longitudinal vibrations.) Light consists of transverse vibra-
tions ; air and water have no rigidity, yet they are transparent, i.e., trans-
mit transverse vibrations ; hence it must be the ether inside them which
really conveys the motion, and ether must have properties which, if it
were ordinary matter, we should style " inertia and rigidity."
This electrical ocean,in which we and everything else are immersed,
has been likened by Sir William Thomson to a mass of jelly which allows
all bodies to pass through it without friction, which is perfectly fluid for
steady forces, but rigid for infinitesimal vibrations, and, as water is con-
tained in jelly, so is electricity contained in the ether. Electricity thus
becomes a mode or manifestation of the ether, as heat is a mode of motion
of material particles. Conductors are bodies which allow electricity to
flow through them,—when immersed in such a medium, they become
cavities or channels. But electricity is entangled in such a medium, and
through this it cannot penetrate without violence or disruption. Yet
bodies can move freely through it. The electricity is alone entangled.
The cavities, cracks, or spongy bodies, which are pervious, but with more
or less frictional resistance to the flow of liquids through them, are the
conductors. The insulators or dielectrics are like elastic or impervious
partitions, but yielding masses, subject to strains when electricity is
moved. As a general definition it may be said that all transparent sub-
stances (not fluids) are insulators, and that all opaque bodies are con-
ductors.
By insulating, i.e., supporting on glass stems such opaque bodies as
brass spheres or cylinders, and connecting them by copper wire, you
have so many cavities and tubes in an otherwise "continuous elastic
and impervious medium, which surrounds us and them, and extends
throughout space wherever conductors are not." But we must remember
that all—cavities as well as the rest of the medium—are full of the uni-
versal fluid. We see that if matter were perfectly conducting, electro-
statics would be impossible. It is by pumping electricity from one place
to another, at the same time straining the elastic walls between conduc-
tors, that we make static electricity manifest. There are different ways
of making the presence of electricity manifest: 1. By mechanical means,
as friction, pressure, concussion, cleavage, or mere contact. The latter
seems the essential element. This includes the domain of static, fric-
tional, or Franklinic electricity. 2. By chemical means; this includes
voltaic, galvanic, or dynamic electricity. 3. By means of heat and mag-
A-86
McCLURE.
netism ; this includes thermo-electricity and magneto-electricity. It
must be remembered that the electricity made manifest by these different
methods is exactly the same electricity, and differs merely in intensity
and quantity.
Whether the ethereal theory of electricity will satisfy all the require-
ments of a scientific age or not, I think we can, without hesitation, accept
the fact that electricity behaves exactly as an incompressible and inex-
tensible fluid would behave. It is not meant for a moment that it is a
fluid in the ordinary sense of the word, but that the different methods
enumerated are merely forces applied in moving it freely through con-
ductors and straining insulators or dielectrics, and, if the force applied
is strong enough, bursting the walls confining it.
Electricity always flows in a closed circuit; it is of the utmost
importance to always remember this. A cable across the Atlantic is like
an India-rubber tube already full of water, with both ends opening into
the common ocean at their destination. A force-pump may be used to
force a certain quantity of water out at one end, but just exactly the
same quantity enters at the other end ; so we see that the ocean is equally
as much a part of the circuit as the tube. Electricity obeys exactly the
same laws; the same quantity of electricity enters at one as was forced
out at the other end.
If we place a flannel cap to which a silk thread is attached over one
end of a stout rod of vulcanite (both having been previously warmed),
rub the cap around the rod a few times, then remove the cap and hold
it near a positively-charged pith-ball pendulum, the pith ball is repulsed ;
the flannel is therefore charged positively (as we know, like charges repel
and unlike charges attract). Present the rod to the pith ball, violent
attraction ensues; therefore the rod is negatively electrified. Now re-
place the cap and rub again ; without removing the cap, hold both to an
uncharged pith-ball pendulum, and neither divergence nor attraction
ensues. Thus we conclusively prove that (1) positive and negative elec-
trifications are generated together; in fact, one kind of electrification is
never produced without the other. 2. The positive electrification is
exactly equal in amount to the negative. So that no electricity has
been actually generated ; it has been merely moved from one body to
another, or we might say that electrifying a body positively is adding
something to it; then electrifying it negatively to the same extent will
simply mean taking an equal amount of that something from it. We
have seen that when the vulcanite rod was rubbed there was a transfer
of something from one to the other ; in separating them a short distance
there is a force exerted across the air or dielectric tending to bring them
together. Faraday would have said that they are connected by lines
of force, and that these lines tend to shorten and thus bring them
together. At present we say that the medium between them is in a state
of strain.
STATIC ELECTRICITY AND MAGNETISM. A-87
In an ordinary electrical machine we rub glass with some other sub-
stance, such as leather. The rubbing in this case has no special action
in the transfer of the electricity ; it is not the cause of the electricity in
the same sense as it is the cause of heat. It is most likely that simple
contact between dissimilar substances is the essential condition. Fric-
tion brings into close contact numerous particles of the two bodies; it
also cleans, warms, and dries the surfaces; these all favor insulation, and
so prevent the escape of electricity. Practically, to obtain marked elec-
trical effects from the contact of two insulators, they must be rubbed
together. When two conductors are brought together, such as zinc and
copper, they are charged with electricity of opposite sign. Friction here
neither increases nor diminishes the charge; as metals are conductors,
the charge is instantly distributed. This charge is much more feeble
than when two insulators are rubbed together. When the glass is rubbed
by the leather, a transfer of electricity is effected,—the electricity on the
rubber is conveyed to the earth ; that on the glass accumulates on an in-
sulated conductor, and, as it is surrounded by an insulating atmosphere,
it does not escape. The electrical machine here acts exactly like a pump
attached to two bodies, respectively, driving some electricity from one
to the other, giving one a positive charge and the other a precisely equal
negative charge. One body is the earth and the charge therefore makes
little difference to it. The act of charging a conductor is analogous to
pumping water into an elastic bag, or, better, into a cavity in the elastic
medium that we have previously been considering; the medium's thick
walls, extending in all directions, need great pressure to strain them.
We now come to the most important principle in static electricity.
The Seat of Charge of Electricity is the Outer Surface of Conduc-
tors.__Consider two cavities in this elastic medium, or, better, draw them
on a piece of paper and " consider fluid pumped from one to another,
and you will see the charge (i.e., the excess or defect of fluid) resides on
the outside. If the fluid is exactly incompressible, not the least extra
quantity will be squeezed by the pressure into the space originally occu-
pied by the cavity. You may show that when both cavities are similarly
charged the medium is so strained that they tend to be forced apart;
whereas, when one is distended and the other is contracted they tend to
approach. Further, you may consider two cavities side by side, pump
fluid into (or out of) one only, and watch the effect on the other. You
will thus see the phenomena of induction,—the near side of the second
cavity becoming oppositely charged (i.e., the walls encroaching on the
cavity), the far side similarly charged (the cavity encroaching on the
walls), and the pressure on the fluid in the cavity being increased or
diminished in correspondence with the rise or fall of pressure in the
inducing cavity."
If we take a cylindrical glass jar and coat it, both inside and out-
side to within two or three inches of the top, with tin-foil, we make a
A-88
McCLURE.
Leyden jar. Place such a jar on an insulating stand and connect eithei
coating, by means of a chain, to the conductor of an electrical machine,
and work the machine for a short time. As the coating in connection
with the machine has received a charge, we should expect to get a spark
if we connected the coatings together, say, with the hand. If we get a
spark at all, it will be an extremely feeble one. Now let us connect as
before, say, the inner coating to the conductor of the machine and the
outer coating to the earth, by means of a chain or the hand. If we turn
the machine as many times as before, a very strong spark will be obtained
by presenting a finger to the inner coating, thereby connecting it through
the experimenter's body and the earth with the outer coating. All elec-
trical charging of bodies is exactly analogous to the charging of a
Leyden jar; so we have here the key to the whole problem of electro-
statics. We cannot charge one body alone, we cannot charge one coating
of a Leyden jar alone; an exactly equal charge must be given to the
other coating. When we charge an insulated conductor in a room, the
walls and floor of such room represent the outer coating, the inner coat-
ing being the conductor; the air, with its contained ether, the dielectric,
and is analogous to the glass in the jar. We have seen that we cannot
charge an insulated Leyden jar. If we had a pith ball attached to each
coating, both would rise equally and simultaneously when the attempt
is made to charge the jar. Their levels or potentials would be equal,
therefore no spark would pass. In fact, we have been trying to force an
absolutely incompressible fluid into a space already full of such fluid.
When we connect the outer coating of the jar to the earth we allow of
the escape of just so much electricity as we pump in from the electrical
machine ; so, to charge a Leyden jar, for every spark we give the inner
coating we must take an equal spark from the outer coating. This may
be made plainer by thinking of the coatings of the jar as two India-
rubber tubes (conductors) and the (dielectric) glass as an electric
diaphragm uniting the tubes. The tubes are filled with water, and one
end connected to a pump; we now close the end farthest from the pump
by a second sheet of India rubber. If we then work the pump, the
elastic diaphragm (dielectric), which does not allow water to pass, is
stretched slightly, moving the water a little forward on the other side
of the diaphragm, and thus to a slight extent stretching the elastic cov-
ering on the farther side of the tube. If the pump is removed, there is
a small recoil of the elastic, and any extra water that has been forced in
escapes again from the end of the tube which was connected with the
pump. This represents the small spark from the charged insulated
Leyden jar.
In the second experiment the outer coating of the jar was in con-
nection with the earth. Therefore we must now remove the elastic
covering from the farther end of the tube, and allow both ends to dip
into a tank with which the pump is also in connection. It is well here to
STATIC ELECTRICITY AND MAGNETISM. A-89
remember that electricity always flows in a closed circuit. When the
pump attached to the near end of the tube is now worked, water will be
forced into the tube representing the inner coating; at the same time
the diaphragm is stretched, and exactly the same quantity of water will
be forced from the tube representing the outer coating. The pump may
be worked so as to strain the diaphragm (dielectric) very greatly or
even to burst it. If the force (pump) be now removed, we have a quick
recoil of the diaphragm (dielectric), the extra quantity of water is again
forced out at the pump end of the tube, the equilibrium being adjusted
by the water of the tank entering the far end of the tube. In this
experiment the quantity-of water forced in has been much greater, the
diaphragm has been stretched to a much greater extent, and the recoil
(spark) has been more powerful. In the case of the jar, given a
sufficiently-powerful machine the electrification may be increased until it
either overflows or discharges through the glass, which would be broken
in the process. If the jar is properly constructed, the tin-foil will be
taken up so near the edge that the discharge, when it takes place, will
occur through the air, instead of the glass, thus saving the jar.
These experiments can be also made to illustrate the process of
induction. If we bring a charged body near an insulated conductor,
we drive electricity of like sign to the far side of the conductor, and
electricity of an opposite sign we attract to the near side. If we now
connect the far side of such conductor to the earth, by means of the
fino-er or a wire, we allow this electricity to escape, and we have two
bodies oppositely charged, separated by a dielectric. The same thing
occurs in the Leyden jar and its analogue, the India-rubber tube. We
found that when the jar was insulated it refused to charge, but when we
connected the outer coating with the earth we had the two equal and
opposite charges separated by the dielectric (glass). It has been con-
clusively proved, by examining the glass under such conditions by means
of polarized light, that it is in a condition of strain.
We have looked at electricity in the foregoing from Franklin's point
of view, i.e., that there was one electricity. A positive charge meant an
excess, a negative charge meant a deficiency, of the universal fluid. This
view seems to fit in well with the examples given of pumping an incom-
pressible fluid into elastic cavities with thick walls, spongy bodies, and
elastic bags, and thus stretching the walls. There is an obvious defect
in the analogy, as the volume of the cavity is increased or diminished
when we pump fluid into or out of it. We know—when we charge a
conductor—that there is no change of volume in the conductor. So we
have to map out, as it were, and think of the original space inside the
cavity in its unchanged condition, already full of the incompressible fluid,
as the true conductor. You cannot fill it any fuller, therefore the excess
or defect of fluid would be on the outside, i.e., in the dielectric. This
might be obviated by viewing electricity as composed of two separate
A-90
McCLURE.
entities, and not looking at negative electricity as mere negation. There
are many reasons for thinking that this represents the true state of the
case,—the facts of electrolysis—the two opposite processions of atoms—
conveying their charges of positive and negative electricity in an elec-
trolyte. The electrical flow in opposite directions on the Holtz machine,
the strain phenomena in a dielectric, would be explained by the molecules
in such dielectric being stretched by their oppositely-charged atoms, the
tearing asunder of the molecules as being disruptive discharge, which is
undoubtedly of an electrolytic nature ; so we would have, as in an elec-
trolyte, two opposite processions of atoms carrying their electric charges.
Static Electricity, or Electricity at Rest, or, rather, in a
State of Strain.
In the previous pages I have endeavored broadly to give a general
view of the whole subject of static electricity, utilizing the ethereal elec-
trical theory, as propounded by Professor Lodge, as a means of adding
more defmiteness and reality, than is given in most text-books, to electrical
phenomena. We must now endeavor to treat this subject more method-
ically ; but I hope the general view already given will be a material aid
to a more.perfect understanding not only of this branch of electrical
science, but also of its action on the human body.
CONDUCTORS, INSULATORS, AND ELECTRODES.
We have seen that certain bodies allow electricity to pass through
them and are called conductors. Bodies which do not allow electricity,
or allow it with difficulty, to pass through them are called insulators, or
dielectrics. The metals, charcoal, water, solutions, and moist bodies, such
as the earth, are conductors. Air, whether damp or dry, and all gases,
including dry steam ; most kinds of glass, sulphur, India rubber, vulca-
nite, shellac, gutta-percha, and other resins; some oils, dry silk, and
cotton, are insulators. Wood, stone, and flax are imperfect insulators.
The difference between conductors and insulators is one of degree only ;
all solids and liquids resist the passage of electricity to some extent, and
none prevent that passage entirely.
The insulator plays an important role in the application of static
electricity. If the patient is not well insulated there is a great waste of
electricity and the power of the machine may be quite neutralized. The
most perfect insulator is a platform of glass having glass supports about
twelve inches in length.
The electrodes required need not be many ; they should include a
large and small brass ball, a metal point, a wooden point, and a wooden or
ivory ball. A metal-cap electrode for the head is a good means of pro-
ducing the souffle. The ear-electrode is made of vulcanite formed into the
shape of an ear-speculum and pierced with a brass wire. In applying this
STATIC ELECTRICITY AND MAGNETISM. A-91
to the ears care must be taken that the sparks to be drawn should be very
small; a wooden point or ball should be used in preference to metal.
MODES OF PRODUCING AN ELECTRIC CHARGE
We have seen that rubbing two different substances together is the
usual method of producing an electric charge. Each substance in the
following list usually becomes positively electrified when rubbed or
pressed against any of the substances placed after it, but negatively elec-
trified when rubbed or pressed against any substance preceding it in the
list. We obtain the most marked effects by using pairs of substances
which are far apart in the list: cats' fur, glass, ivory, silk, the hand,
wood, sulphur, flannel, cotton, shellac, caoutchouc, resin, gutta-percha,
metals, and gun-cotton.
Two conductors in contact, whether solid or liquid, charge one
another with electricity of opposite sign. Friction between the metals
neither increases nor diminishes the charge. As metals are conductors,
the electricity is instantly distributed over them. When insulators such
as glass or resin are pressed or rubbed together, only those parts which
come into actual contact are at first electrified. The electricity in time
spreads farther because the insulation is imperfect. Two insulators
which have been rubbed together retain their charges unmodified for
some time after their separation; this is not the case with conductors.
FORCE BETWEEN ELECTRIC CHARGES.
Bodies charged with electricity of the same kind repel one another
by virtue of their charge ; bodies charged with opposite electricity attract
one another. The fluid with which any body is charged cannot leave the
body, being retained by the surrounding dielectric; any force acting on
the electric fluid acts, therefore, on the dielectric. Equal charges under
equal conditions produce equal forces. We thus have the means of ascer-
taining whether two bodies—say, spheres of equal diameter—are equally
charged with electricity; to do this we have only to observe whether, at
equal distances, they exert equal forces on a third body charged with
electricity. Means exist by which equal charges can be added so as to
accumulate on one conductor, and we find by experiment that two equal
quantities of the same sign, when thus added, attract or repel a given
charge, on another body, with twice the force which was exerted by each
singly, when in the same place ; also that two equal quantities of opposite
sign neutralize one another so as, after their combination, to exert no
force. These facts enable us, independently of all hypothesis as to the
nature of electricity, to treat an electric charge as a measurable quantity.
Instruments for numerically measuring or comparing the forces due to
various charges of electricity are called electrometers. Instruments
which simply indicate the existence of a force due to a charge are called
A-92
McCLURE.
electroscopes. The unit quantity of electricity is that which repels an-
other equal quantity at a unit distance with unit force.
DISTRIBUTION OF ELECTRICITY ON CONDUCTORS.
Electricity, as we have had occasion before to emphasize, resides on
the surface of conductors. That this is absolutely true the well-known
experiment of Cavendish or Biot proves. If an insulated metal ball be
strongly charged with electricity and we place two hemispherical metal
envelopes furnished with glass handles on the sphere so as to envelop it,
after contact with the sphere, carefully remove the hemispheres, and by
means of the glass handles bring them near an uncharged gold-leaf elec-
troscope, in each case the leaves diverge ; now bring the ball near the
electroscope, the leaves do not diverge, although the ball originally re-
ceived the charge. We see that the charge has passed from the surface
of the ball to that of the covers. This is what we should expect if we
recall the experiment with the cavities in the elastic medium ; " elec-
tricity being exactly incompressible, not the least extra quantity will be
squeezed by pressure into the space originally occupied by the cavity."
Even if the conductor be hollow and the charge be given to the inside,
the result is precisely the same; it immediately flows to and over the
surface. Many experiments might be adduced to prove this law.
Faraday had a cube-shaped room constructed and rendered a free
conductor of electricity in every part. This chamber was insulated in
the lecture-room at the Royal Institution. He went into this cube and
lived in it, " used lighted candles, electrometers, and all other tests of
electricity, and could not find the least influence upon them or indication
of anything particular given by them, though all the time the outside of
the cube was powerfully charged, and large sparks and brushes were
darting off from every part of its outer surface." Mr. Boys has shown,
by means of two soap-bubbles, one inside the other, that electricity did
not penetrate the wall of the outer bubble, a soap-bubble being a con-
ductor of electricity.
REDISTRIBUTION AND SUBDIVISION OF CHARGES.
If an insulated conductor is charged so as to be unaffected by other
electrified bodies, and any portion of that charge be removed, the remain-
ing electrification will distribute itself over the surface in a manner similar
to the distribution of the original charge. Suppose, for example, that
we have several insulated metallic spheres of equal size, one of them
being charged with a certain quantity of electricity and the others un-
charged. If one of the latter be brought in contact with the charged
sphere it will receive half the charge ; if on separating the spheres either
be brought in contact with another uncharged sphere, it will receive half
its charge, i.e., one-fourth of the original charge. The distribution in
each case will be uniform.
STATIC ELECTRICITY AND MAGNETISM. A-93
POTENTIAL.
The quantity of electricity in an electric charge is a conception
analogous to that of a quantity of material fluid. So the idea of elec-
trical potential is analogous to that of level in a body of water; that is,
level as indicating a condition by which gravitating matter, such as
water, can do work in descending to a lower level. The electrical poten-
tial of a conductor is that condition of the conductor in virtue of which
the electricity tends to pass from the conductor to the earth, and in so
passing do work,—the earth being considered at zero potential.
DENSITY.
The density of a charge at any point is the charge per unit area at
that point. The density of a charge is uniform on all conducting spheres
when they are unaffected by the proximity of other conductors. When
the thickness of the dielectric between two conductors is variable the
density of charges induced between them tends to be greater the nearer
they approach. The density of any charge tends to be greater at all
projecting edges or points. The electricity on any small area of an elec-
trified surface is acted on by a force normal to that surface. This force
tends to stretch the conductor outward, or tear off a part of its surface,
and is called the electric stress, or tension, at that part of the surface.
Stress or tension is measured in units of force per unit of area, and is
proportional to the square of the density on the element of surface.
ELECTRICAL CAPACITY.
If we take two unequal-sized vessels and fill them with water,
the quantity of water they will hold, of course, depends on their size or
capacity. -Similarly, if we take two insulated conductors of the same
shape, but of different size, and electrify them, the large one must have
a greater charge than the small one to electrify it to the same potential,
—i.e., the large one has a greater electrical capacity than the small one.
Thus, the potential of a conductor depends both upon its charge and
its capacity ; in fact, if C equals the capacity of a conductor, Q the
charge or quantity of electricity, and Y the potential, then C equals |.
CONVECTION—sparks; points; silent discharge; brush.
Convection occurs when electricity is conveyed from one place to
another by small particles of matter, which they carry as a charge. A
charged conductor can be discharged by convection if steam or spray be
blown to or from it; each globule of water leaving the conductor carries
away a charge of electricity. When two conductors of different poten-
tials are brought close together, one or more sparks will pass between
them. The spark consists of white-hot matter electrically charged. The
disruption of this matter from the body is caused by the breaking down
A-94
McCLURE.
of the strain in the dielectric ; the heat and light observed are due
to the mechanical action of the disruption,—as when a spark is struck
by a steel upon flint, the spark is not electricity. In a conductor
charged to a high potential the electricity escapes from any sharp points
or edges. The action is one of convection by a stream of particles pro-
ducing an actual current in the air, and is due to the stress at the points
or edges. When the action is unaccompanied by noise or light, it is
called a silent discharge ; when accompanied by noise or light, the term
brush is applied to the phenomenon.
As we have to deal with the human body as electro-therapeutists, it is
well that we should keep constantly before our minds that if we have a
patient on the insulated stool, and connected by means of a conductor to
one of the poles of an electric machine, and if the other pole is also con-
nected to the patient, the stool, or platform, while we work the machine,
there seems to be no effect; we cannot get the faintest spark from our pa-
tient, yet we are moving electricity in a closed circuit; a current is flowing.
It is as if an India-rubber tube were attached to a pump, the free ends of
the tube dipping, into the same tank. Here we are dealing with the purely
conducting elements ; the strain phenomena are absent, therefore we can
have none of the effects of static electricity, and the current which is
flowing is so small that it is not appreciated by the patient. The reason
we get such a small current is that, though we have got an enormous
electro-motive pressure or potential (60,000 volts; say, equal to a bat-
tery of 60,000 Daniell cells), the resistance in the machine is so great
(since there are so many dielectrics between the rubber and the prime
conductor) that the electricity is almost all expended in overcoming this
tremendous resistance, amounting to possibly millions of ohms. But if
the conducting chain in connection, say, with the negative pole be
allowed to fall to the earth, and the machine worked, a different state of
things is seen. The patient is charged with positive electricity; at the
same time the walls or floor of the room are charged with exactly the
same amount of negative electricity,—that is, the positive charge on the
patient has, by induction across the dielectric, produced an equal and
opposite charge.
Now, if we approach the patient with an earth-connected conductor,
—that is, a conductor in connection with the walls or floor of the room,—
the charge of electricity is increased; " the capacity of a conductor is
increased by bringing an earth-plate near it," the reason being that we'
are simply thinning down the dielectric. The thin-walled elastic medium
takes much less force to distend it than would the thick mass of dielectric
reaching from the body to the walls or floor of the room. By approach-
ing the body with an electrode connected to the earth by means of a
chain, we do this; and when the ball of the electrode has been brought
near enough, the strain in the dielectric has become so great that it
breaks down, a disruptive discharge ensues, accompanied by a spark.
STATIC ELECTRICITY AND MAGNETISM. A-95
In fact, we have converted static into kinetic or current electricity,
having electrolytic heating and other effects of a true current. But it is
oscillatory in character ; the rapidity of this oscillation is very great,
and may reach as high as a hundred million vibrations per second.
We have arrived now at a point of the greatest importance to the
electro-therapeutist, and that which requires most careful consideration.
We have seen that the insulated body in connection with the machine is
virtually the inner coating of the Leyden jar, the outer coating being
represented by the electrode in the hands of the operator; the dielectric
between them—as we have had frequent occasion to mention—is in a
condition of strain. The force producing the strain is a " stress," or, as
it is sometimes called, the electric tension ; at the point opposite the
ball of the electrode there is a tendency to stretch this part of the body
outward, as it were, to tear off part of the surface. When the spark
occurs there is a quick forward movement of the electricity away from
the body, with an equally rapid recoil. The duration of the whole spark
has been estimated to be all over in the hundred thousandth of a second.
If we view the human body as a conductor, such a current would, I am
afraid, penetrate to no appreciable depth. But experience tells us that
a static-spark current does penetrate. To my mind, we must get rid
altogether of the idea of thinking of the human body as a conductor
in the same sense that we speak of metal as being a conductor. It con-
ducts electricity, it is true ; but it conducts it very badly. Nearly all
bodies will conduct electricity more or less ; but my contention is, that
the human body is made up of conductors and insulators, or dielectrics;
the skin with all the transparent tissues are dielectrics, the fluids being
conductors. Now, this is just the combination that we require to trans-
mit the spark current; and the electricity that resides upon the surface
of conductors, as it were, soaks in here. If an insulated conductor be
placed in a polarized dielectric between a charged conductor and the
other conductor be an earth-plate facing it, and a constant difference of
potential be maintained between them, the electricity in the dielectric
acts inductively on the conductor, inducing a negative charge on the
near side and a positive charge on the far side; the electricity has, as it
were, slipped through the conductor, and the insulating medium has to
bear a greater strain, though the electro-motive force is the same and
the charge is increased.
If the dielectric were supposed to be stratified, each stratum of such
dielectric, being strained, pushed forward like an elastic partition by the
electricity trying, as it were, to get to the conductor whose potential is
lower, then, if one of these strata gave way, there would be some further
forward movement of the electricity, but the strain would have to be
borne by fewer strata; the strain, therefore, on those remaining would be
greater. By placing a conductor in a polarized dielectric we replace one
or more of such strata. The human body, as I have said, is a very bad
A-96
McCLURE.
conductor of electricity; this is common knowledge to us all in death
from lightning. We know that it makes little difference what metal we
use for a lightning-conductor, as the electricity slips along on the extreme
outer skin, and does not penetrate sufficiently to find out whether the con-
ductor be silver, copper, or iron. With Faraday's conducting-tube experi-
ment before us, I think we must be compelled to view the human organism
as made up of dielectrics and conductors ; I do not see any reason to de-
part from the former statement I have made—though now dealing with
organic matter—that insulators are transparent bodies, and conductors
are opaque. The skin I consider a dielectric,—I do not say a perfect die-
lectric ; there may be strata that slip more or less like the conductor in a
polarized dielectric, though I should say that none of them slip so much;
there is, however, a likelihood of differences in bearing strain. Static elec-
tricity having penetrated far, there may be next some fluids that allow a
complete slip, electrolytic action being the means of conveying the elec-
tricity to the next dielectric (some transparent tissue,—sheaths of nerves,
forms of fibrous tissue, etc.), which entangles the electricity and takes up
the condition of strain, and so on. All this, let it be remembered, is due to
static electricity alone, the body being charged from the prime conductor
of the machine. It is hard to conceive, without such an explanation,
what possible benefit is to be derived from static insulation alone (elec-
tric bath, or the souffle (electric wind); but I, for one, have not the
slightest doubt of the excellent effects derived from the two latter appli-
cations of static electricity, independent of all suggestion or expectant
attention. Now let us see what occurs at the moment of discharge. The
electricity is straining the dielectric, both inside and outside the patient's
body. Of course, the air part of this strain is the more perfect, as there
are fewer slipping strata ; in the dielectric within the body, however, there
may be a good deal of this, causing a certain amount of leakage; so that
the air strata have to bear the greater part of the strain. At the moment
of discharge the elastic partitions or strata are broken down, the elec-
tricity is released—it surges forward—and as rapidly recoils backward.
An obvious fact is that when the distorting force is removed the medium
will spring back to its old position, overshoot it on the other side, spring-
back again, and thus continue oscillating till the original energy is
rubbed away by viscosity or internal friction. Now released, there is no
dielectric to restrain it; it is a true current, but an oscillating one.
MACHINES.
We have seen, first, that bodies may be electrified by friction ; sec-
ondly, by induction or proximity to an electrified body; thirdly, that
electrified bodies not only attract non-electrified bodies, but communicate
electricity to them by contact; and, fourthly, that bodies similarly elec-
trified, either by each other or from the same source, show mutual re-
pulsion. These principles underlie the construction of all electrical
STATIC ELECTRICITY AND MAGNETISM. A-97
machines. The simple plate-glass machine consists of a large disc or
plate of glass revolving on a horizontal axis, the axis of the plate passing
through wooden supports, and the handle which turns the machine is
made of glass ; as the glass plate revolves it is rubbed against by two sets
of rubbers, one above and the other below ; at an angle of ninety degrees
from each of these rubbers there is fixed a bent brass rod, surrounding
but not touching the edge of the plate, and furnished on the side pre-
sented toward the plate with small, projecting spikes ; these two brass
rods are attached to the ends of a thick brass conductor, supported on
Fig. 1.—One Form of Plate-Glass Machine (The Rdmsden).
an insulating stand, usually made of glass. This is known as the prime
conductor ; it need not have any special form, except that every part of
it must be rounded, with the exception of that presented toward the
glass plate, as we have seen that the electricity of a conductor always dis-
tributes itself entirely on the surface of such conductor, and in such a
manner that the accumulation of electricity is always greater at the most
pointed parts, and least at the most rounded. As we have seen that the
electricity upon any conductor tends to drive away the electricity upon
another conductor in the neighborhood, so, in like manner, the electricity
on a conductor behaves to the electricity on the same conductor. At
7
A-98
McCLURE.
every point of a conductor there is a force acting outward from it which
tends to break down the insulation of the air or other dielectric surround-
ing the conductor, and to cause the escape of the charge. This force is
greatest where the accumulation is greatest.—at the most pointed parts, in
other words. It follows, therefore, that the conductor should be round—
having no points or edges—except opposite the glass disc; for here we
wish to facilitate the flow of electricity between the conductor and the
glass. Before using the machine a little amalgam of mercury and tin
rubbed up with some tallow is smeared over the rubbers, as this is found
to promote the transfer of the electricity. When the handle is turned
and the glass plate revolves, it becomes electrified positively by friction
against the rubbers. The rubbers at the same time become negatively
electrified, which electricity flows to the earth ; or, as far as our knowl-
edge goes, we may say, with equal reason, that the rubbers lose positive
electricity, and, to supply this, more positive electricity flows up from
the earth to the rubbers, and the rubbers are connected to the earth. As
the plate turns around, the positive electricity is brought opposite to the
points. The positive electricity on the plate, as the latter passes between
the points, drives the positive electricity of the prime conductor to the
farther part, and therefore leaves the points and that portion of the
prime conductor in their neighborhood with a deficiency of positive elec-
tricity, or, as we may say, electrifies them negatively. There will there-
fore be a force acting upon the electricity on the points, tending to drive
the negative electricity outward from the points toward the glass, or, in
other words, tending to draw positive electricity away from the glass
plate on to the points of the conductor. The part of the glass plate
opposite the points thus loses the greater portion of its charge. In
passing through the second pair of rubbers, it again becomes charged as
before; this charge is delivered up to the second set of points. This
process continues until the potential of the conductor is so nearly equal
to the potential of the plate that the force between them becomes too
small to cause any further transfer of electricity. If, however, some
outlet be provided for the electricity which accumulates upon the prime
conductor, the action may be continued indefinitely. This is the simplest
form of electrical machine, but is seldom used in medicine.
At the present time influence or induction machines are very gener-
ally used by electro-therapeutists. Before studying their action, it would
be as well to give a short description of an "electrophorus." This simple
instrument was invented by Yolta, in 1775, for obtaining a series of
charges of electricity from a single charge. It consists of (1) a gener-
ating plate,—a flat, round cake of resin, sealing-wax, shellac, or vulcanite
contained within a metal dish or resting upon a metal plate; (2) this me-
tallic plate or dish is called the " sole "; (3) a disc of metal of slightly
smaller diameter, having attached in the centre an insulating handle,
which is called the cover or collecting plate. The method of charging is
STATIC ELECTRICITY AND MAGNETISM. A-99
as follows : We warm the generating plate until it is quite dry, then rub
it with flannel or strike it with a fox's brush; this makes negative elec-
tricity manifest on the upper surface of the cake; now, as we know, the
cake is a dielectric, and the layers or strata composing it are in a state
of strain, consequent on the charge it has received ; it induces positive
electricity on the upper part of the sole, and, as the cake is uninsulated,
the negative electricity escapes to the earth, or, as we might say, a posi-
tive charge comes from the earth. So the plate has a positive charge of
electricity and the cake a negative charge. Place the cover, by means
of the insulating handle, on the generating plate ; the two discs do not
touch intimately, for there is an air-film between them ; we have therefore
a negatively-charged body separated from a conductor. The consequence
is that induction takes place,—a positive charge attracted to the lower
side of the disc, a negative charge repelled to the upper surface. If the
cover is touched with the finger, the free negative electricity escapes
through the body to the earth, or we may regard it as being neutralized
by positive electricity flowing from the earth through the body and
hand. Remove the finger, and the positive charge on the cover is, as it
is said, " bound " by the negatively-charged plate. The cover is then
lifted by the insulating handle, and is found to possess a charge of posi-
tive electricity sufficiently strong to yield sparks when the knuckle is
presented to it. If the generating plate be perfectly dry, this may be
repeated many times from the same charge given to the cake. These
series of events go on rapidly and continuously in all influence or induc-
tion machines. Suppose we have an insulated, uncharged conducting
vessel or shell, B, and a positively-electrified conductor, A, insulated, and
we introduce A into B, not touching the side, the interior surface of B
will be charged by induction with a quantity of negative electricity equal
to the quantity of positive electricity on A; at the same time the exterior
surface of B will be charged with an equal quantity of positive electricity.
The position of A inside B will not affect the amount of these charges.
It will affect the distribution on the inner surface of B, but on the
exterior surface of B the distribution will be unaffected by the position
of A, being determined by the form and position of the walls and floor
of the room where the experiment is performed; changing the position
of A inside B will not affect the potential of B. If A be allowed to touch
B, the opposite charges upon their opposed surfaces cancel each other,
leaving B wholly charged with a quantity of positive electricity equal to
that originally on A. If A be now withdrawn, recharged with positive
electricity and introduced inside B without touching, it will induce a new
negative charge on the interior of B; a new positive charge will now be
added to that already on the outside of B. If A now touches B, the
opposed charges on the opposed surfaces will again cancel each other,
leaving two positive charges on the exterior of B ; this process can be
repeated any number of times, so that we can give B an indefinite num.
A-100
McCLURE.
ber of charges. When A is wholly inside B each charge added raises the
potential of B, which may be raised in this way indefinitely above that
to which A is charged by the source of electricity. In bringing A
toward B while both bodies are charged, say, positively, we work to
overcome their repulsion, and by the time A has passed inside B there
has been sufficient work done to raise the potential of A above that of B ;
though A when it received its charge was at a much lower potential than
B. We see that a charged body introduced inside a conducting shell,
and then brought into contact with it, gives up its charge wholly to the
shell, no matter what the relative potentials of the two conductors may
have been before the one was brought inside the other.
All induction or influence machines depend, for their actions, on the
foregoing principle. If we take two such insulated shells, B and C, and
give a slight charge of positive electricity to B ; and now take an insu-
lated brass ball and bring it near the conducting shell, B, but not touching
it, the positive charge on B induces a negative charge on the side of the
ball next it; we now touch the ball with the finger, and the effect is we
withdraw the repelled positive charge, leaving the ball with a negative
charge. Now place the ball inside the uncharged shell, C, and allow them
to touch. As we have previously seen, the negative charge is entirely
given up to the shell, C. If the ball be removed from C and held near
the outside of C, a positive charge is induced on the side of the ball next
C and a negative on the other side. Touch the ball with the finger and
the negative charge is conveyed to earth, and we have the ball with a
positive charge ; this charge can be given up to B by placing the ball
inside it and allowing it to touch, which increases the positive charge
already on B. This increased charge on B is then used, in the same
manner as the original one, to electrify the ball negatively, and, the
charge on B being increased, the negative charge on the ball will be
greater than before. This is given up to C in the same manner as before,
and the increased negative charge on C is used to develop by induction
an increased positive charge on the ball, which is transferred again to B.
If we continue this process, the difference of potential between C and B
may be so increased that if they are brought close together a spark will
pass from one to the other. An influence machine simply consists of an
arrangement for carrying on such a series of operations as has just been
described in rapid succession.
A revolving carrier or series of carriers is used, together with an
inductor or series of inductors, between which and the carrier a certain
small difference of potential must be excited in order that the machine
may start. The carriers as they pass the inductors are electrified by
induction, and when passing out of the influence of the inductor they are
touched by a spring in connection with a collector, which in its turn acts
as an inductor, and in this way a very small difference of potential can
be rapidly increased to a considerable extent. With the other forms of
STATIC ELECTRICITY AND MAGNETISM. A-101
influence machines it was necessary to begin by electrifying one of the
conductors. Influence machines, however, are now made which are able
to excite themselves without external assistance, by means of a small dif-
ference of potential which invariably exists between the inductors, and
which is sufficient to begin the series of operations.
The lower part of Carre's dielectric machine, as seen in the cut, is a
plate of glass supported on vulcanite pillars; in fact, is an ordinary
plate-glass machine with only one set of rubbers, which are uninsulated ;
it is turned by the ordinary handle; above this and on supports, over-
lapping the glass disc in its upper half, is a larger disc of ebonite, which
is made to revolve at the same time as the glass disc, but necessarily at
much greater speed; both plates are surmounted by a large brass
Fig. 2.—The Carre Dielectric Machine.
cylinder,—the prime conductor,—from which projects a brass rod having
a number of points for collecting the electricity from the ebonite plates.
We thus see an illustration of the electrophorus, a quantity of electricity
being supplied by the glass plate, but which is positive electricity of the
same sign appearing on the side of the ebonite plate next the points ; the
upper set of points, F, taking up the positive electricity ; the lower set,
E, being connected to the earth by means of the chain.
This machine is made in three sizes, all of which produce a fair
quantity of electricity. The second size is the one generally used by
electro-therapeutists, the diameter of the ebonite plate being twenty-one
inches, that of the glass fifteen inches. This machine, under favorable
conditions, gives a spark of about ten inches. It is very reliable in
most atmospheric conditions.
A-102
McCLURE.
The Wimshurst influence machine consists of two circular discs of
ordinary window-glass, mounted upon a fixed horizontal spindle in such
a way as to be rotated in opposite directions, at a distance apart of not
more than one-eighth of an inch. Each disc is attached to the end of a
boss, of wood or ebonite, upon which is turned a small pulley. This is
driven by a cord or belt from a large pulley, of which there are two,
attached to a spindle below the machine, and which is rotated by a winch-
windle, the difference in the directions of rotation being obtained by the
crossing of one of the belts. Both discs are well varnished, and cemented
to the outer surface of each are twelve or more radial,, sector-shaped
plates of thin brass, disposed around the discs at equal angular dis-
tances apart. The two sectors situated in the same diameter of each
Fig. 3.—The Wimshurst Influence Machine.
disc are twice in each revolution momentarily placed in metallic connec-
tion with one another by a pair of fine-wire brushes attached to the ends
of a curved rod, supported at the middle of its length by one of the
projecting ends of the fixed spindle upon which the discs rotate, the
brass sector-shaped plates just grazing the tips of the brushes as they
pass them. The position of the two pairs of brushes with reference to
the fixed collecting combs, and to one another, is variable, as each pair
is capable of being rotated on the spindle through a certain angular dis-
tance; and there is, as in the case of the collecting commutator brushes
of dynamo-electric machines, one position of maximum efficiency. In
this machine it appears to be when the brushes touch the discs on
diameters situate about forty-five degrees from the collecting combs and
STATIC ELECTRICITY AND MAGNETISM. A-103
ninety degrees from one another. The fixed conductors consist of two
forks furnished with collecting combs directed toward one another and
toward the two discs which rotate between them, the position of the two
forks, which are supported on ebonite pillars, being along the horizontal
diameter of the discs. To these collecting combs are attached the ter-
minal electrodes, whose distance apart can be varied by the two project-
ing ebonite handles shown in the illustration. These collecting combs
appear merely to convey the electric charge to what may be called the
external circuit, for the induction action of the machine is as rapid and
powerful if both are removed and nothing left but the discs and brushes ;
when in the dark, the machine being worked, the whole apparatus bris-
tles with luminous electricity. The machine is, moreover, self-exciting,
requiring neither friction nor the spark from any outside electric exciter
to start it.
An extract from Nature, May 3, 1883, says : " It appears that in this
machine the metal strips affixed to the plates act both as inductors
and carriers. Suppose the front plate be rotating clockwise and the
back plate counter-clockwise. If the metal strips descending from the
summit on the left on the back disc are charged positively, the metal
strips ascending on the front disc from the left will, as they pass under
the momentary touch of the brush, acquire a negative charge. As these
negatively-charged strips of the front plate advance toward the right,
they will come to a point where they are opposite to the upper end of the
hinder diagonal conductor, and here, whilst still acting as carriers to
bring the negative charge round to the right side, they will act as induc-
tors, and will influence the strips of the back disc, which will, as they
are in turn touched by the hinder brush, acquire positive charges. The
strips on the front disc will therefore constantly carry a negative charge
as they move over the top from left to right, and those of the.back disc
will carry a positive charge from right to left. In the lower halves of
their respective rotations the inverse of these actions will hold good, the
front carriers conveying positive charges from right to left, the back ones
conveying negative charges from left to right. The result will, of course,
be that the two main conductors on the left and right will become, re-
spectively, positively and negatively charged. If dry and free from
dust the machine excites itself, and, after a couple of turns have been
given to the handle, discharges sparks freely. If the two main conduc-
tors are respectively joined to the inner and outer coatings of a large
Leyden jar, the discharges take place with short, loud sparks of great
brilliancy. If from any cause the machine does not at once charge itself,
gently rub with a silk handkerchief either of the ebonite pillars."
Professor Lewandowski claims that his machine, differing in its con-
struction from all hitherto-known influence machines, answers the thera-
peutist's purpose better than any other ; the merits claimed for it being
that it is uninfluenced by moisture and temperature, as the generating
A-104
McCLURE.
part of the machine is inclosed in a cylinder. The following figure repre-
sents the machine, and the principle of this contrivance consists in the
employment of two hollow drums of idio-electric bodies, of which one is
somewhat smaller than the other and is shut up perfectly air-tight within
the others ; both rotate round the same axis, though in different direc-
tions. The two vertical iron supports, a ax and b&^are screwed to the
Fig. 4.—Professor Lewandowski's Machine.
rectangular wooden frame Ra and Rax, seventy by fifty centimetres, their
tops being joined together by the vulcanite rod, a b. These two uprights
support the axles, e f, W, and WY, which are parallel to each other. The
axle, e f, is fixed and made of steel. Upon the chief axle, e f there are
two vulcanite collars, one of which is joined to the pulley, r, and the
other to the pulley, rL. In the middle of the two collars there are, on the
chief axle, two hard-gum cylinders, one within the other, T, Tx (Fig. 5).
STATIC ELECTRICITY AND MAGNETISM. A-105
The pulley r is connected with the internal cylinder, 2\ ; whereas the
pulley rx is connected with the external cylinder, T; so that the internal
cylinder and the external one can be rotated quite independently.
The two lower axles, IT and Wx, each carry a large pulley, R and Rx,
and a toothed wheel; the large pulleys, R and Rx, are respectively united
by means of straps to the superior pulleys, r and rY. The axle, W,
moreover, carries the handle, k. This whole arrangement allows
the two cylinders to be turned in the reversed direction, when the
handle rotates only in one direction. The wooden frame carries,
besides, two uprights, the lower parts of which are made of glass and the
upper of metal; they terminate in the metallic knobs, m and n. In the
middle of these supports are two metallic knobs, S&and jS&^each carrying
a collecting comb in close proximity to the external cylinder; whilst one
metal double comb, sk skt, inclosed in the small cylinder, is carried by
the fixed axle, ef. In the balls m and n are the conductors, Ax and A2,
Fig. 5.
which can be moved to and fro horizontally. The turning of the handle,
k, brings about the rotation of the outer cylinder, T, through the trans-
mission of movement by means of the pulleys R and r ; whilst at the same
time, in consequence of the turning of the toothed wheel, the axle Wx
rotates in an opposite direction, and this motion carries the small cylinder,
Tx, over by means of the pulleys Rr and rx. If the knobs of the con-
ductors are brought near each other so as to come into contact, when the
handle is turned in any direction it suffices to touch the surface of the
external cylinder with a piece of hard caoutchouc, which has been slightly
rubbed on the clothes, either above or below the middle of the drum
(corresponding with the middle of the inner vertical double comb). This
exciting or charging of the machine is manifested by a whizzing sound.
If the motion be stopped, the electric charge of the cylinders lasts for
several hours. If the handle be turned in the opposite direction, the
machine does not become uncharged.
Atkinson's Toepler electric machine is an electro-static machine, of
A-106 McCLURE.
high tension and large quantity, whose sensitiveness to atmospheric
influences does not interfere with its practical working. It is made with
two circular plates of glass, one stationary, the other revolving close in
front of it; two sets of combs and two Leyden jars, with a switch between
them. To the back of the stationary plate are attached two sets of paper
and tin-foil inductors, connected with which are two wire brushes, and to
the front of the revolving plate are attached six metal carriers with
Fig. 6—Atkinson's Toepler Electric Machine.
raised centres, which are brought into contact with the brushes as the
plate revolves, and generate the electric charge, which is rapidly increased
by induction. Opposite parts of the plates and opposite inductors and
carriers become oppositely electrified, condensation takes place in the jars,
and sparks pass between the sliding electrodes, which may be increased
to seven inches or more in length. Electricity is generated at once, and
the electric charge constantly sustained by the friction of the carriers
STATIC ELECTRICITY AND MAGNETISM. A-107
and brushes ; hence the machine remains in practical working-order under
the most unfavorable atmospheric conditions.
The switch, as seen in the cut, is placed between the Leyden jars,
and in connection with their outer coatings, so that the induced current
between them is controlled by the operator. As this current flows at
the same instant with the discharge between the sliding electrodes
Fig. 7.—Atkinson's Toepler Electric Machine.
connected with the inner coatings, it is only necessary to separate them
to obtain the interrupted induced current similar to the faradic. In con-
nection with the switch are seen cable cords and electrodes, which may
be held by insulating handles and applied to any part of the body.
Opening the switch changes the current to the cords and electrodes, and
on separating the sliding electrodes the faradic effect is at once produced,
which may be varied from the slightest tremor to the most violent mus-
A-108
McCLURE.
cular twitchings. A separation of one-sixteenth of an inch produces a
mild, pleasant sensation ; one-eighth to one-fourth of an inch becomes
painful; while a separation of one-half to three-fourths of an inch can
hardly be borne by the strongest nerves. When the switch is closed and
the sliding electrodes drawn out beyond sparking distance, a person
seated on an insulated platform and connected by cable-cord with the
ball surmounting the Leyden jar farthest from the driving-wheel will
receive a condensed charge of positive electricity, or of negative if con-
nected with the jar nearest the driving-wheel.
In damp, warm weather, a film of moisture sometimes settles on the
glass plates and temporarily, suspends insulation, so that the machine
ceases to generate. The effectual remedy in such a case is to dry and
warm the plates, which may easily be done in a few minutes by placing
one or more kerosene-lamps near them. The warming is as important as
the drying, to prevent further deposition of moisture on the surface.
The Franklinic Interrupted Current and Static
Induction.
A very important advance in the application of static electricity
was made by Dr. Morton, of New York, in 1881. This was the intro-
duction of what he terms the franklinic interrupted and the static
induced currents. As we have seen, in drawing a spark from the patient
on the insulated platform, we break down the dielectric between the
metal ball and his body and, by doing so, cause a real current of elec-
tricity to pass, and close the circuit. The two coatings of the Leyden
jar have been connected. The patient's body is brought in contact with
the earth by means of the chain on the electrode, and, as one pole of the
machine is earth connected, the circuit is thus completed. At the same
time, we must remember that the current we have produced is an alter-
nating one. In this case the patient receives the spark, the circuit being
broken at the patient's body. But we could quite conceive that the cir-
cuit might be broken at any part of it,—say, a foot from the patient's
body,—he himself holding a piece of brass rod or other conductor
having an insulating sheath, the ends of the rod terminating in two brass
balls, and one end of this rod applied directly to any part of the body to
be acted on. If we now, instead of drawing a spark directly from the
body, draw it from the external brass ball, the disruption takes place then
between the external.end of the conductor held in the patient's hand and
the ball of the electrode in the operator's hand. At the moment of the
occurrence of the spark the patient receives the rapidly-alternating cur-
rent through the electrode held in his hand. The current might be
broken at any part of the circuit, and the patient as part of the circuit
feeling the effects. Dr. Morton has constructed an electrode for applica-
tion of the franklinic interrupted current. It breaks the circuit at some
distance from the patient's body; the end next the body may be a moist
STATIC ELECTRICITY AND MAGNETISM. A-109
sponge or other terminal, such as is used in applying the faradic current.
There are two brass balls which constitute the circuit-breaker; these
can be separated and brought together by a movement of the operator's
finger. The spark passes between them and can be regulated by the
distance between the balls.
M$g£f (Q)
Fig. 8.—Morton's Electrode.
STATIC INDUCED CURRENT.
Dr. Morton says: " For this current the electrodes and conducting
cords must be especially constructed ; the metal within the sponge of a
plate should be rolled back upon itself at its edges, so as to present a
rounded peripheral contour, or, better still, it should be a ball of about
an inch in diameter; the handles of the electrodes should be long and
made of ebonite; the conducting cord should consist of a thick strand
of fine wire well insulated by gutta-percha. These precautions are neces-
sary, owing to the great ' tension ' of the current, and its consequent
disposition to break down insulating barriers, which in the case of ordi-
nary currents would suffice to confine them to their proper conductors.
To use the current, bring the discharging rods of the machine into con-
tact. If the Holtz machine, remove the connecting rods which unite the
Fig. 9.—Diagram illustrating Connections for Internal Treatment by the
Static Universal Electrode.
two Leyden jars and hook on the two conducting cords and electrodes.
The patient need not be insulated. If now the wet electrodes be grasped,
the machine set in motion, and the discharging rods separated a very
small fraction of an inch, the current will be felt, and may be graduated
to any strength desired or bearable, and may be localized in its applica-
:Q>
f\
A-110
McCLURE.
tion, internally and externally. In the machine of Carre* jars of about
eight ounces in capacity are used, and are simply suspended from each
conductor by means of a hook; to the outer coating of the jars are
attached the conducting cords with the moist electrodes; the poles in
this machine may be separated for about an inch. The strength of the
current is determined by the size of the jars and amount of separation
of the poles. Nerve and muscle may be acted on in exactly the same
way as in the application of faradism, but, to my mind, in a much more
effectual and less painful manner. I have seen muscles react to this
current when not the slightest reaction could be obtained from the
strongest bearable application of faradism, using both coarse and fine
coil. This form of electricity, by means of special electrodes, can be
used for the vagina, uterus, or other internal canal or cavity (as shown
in diagram)."
-h_______________ —
C=^(\==00---Q*^3
Fig. 10.—Diagram illustrating Static. Induced Current, with Electrodes
for Internal Treatment.
CHOICE OF MACHINE AND METHODS OF APPLICATION.
In the application of static electricity in electro-therapeutics the first
consideration presenting itself is the choice of a machine. Almost all the
types in use at the present time are good. De Yigourout, of Paris, whose
experience of static electricity has been very great, speaks most highly
of the Wimshurst machine and that of Carre*. The Holtz machine ap-
peared to him to give too much electricity and to have too exciting an
effect upon certain patients. He says, " We must not attach too much
importance to these questions of apparatus, but I will say there is an
advantage in using large machines. The discs of the Wimshurst at the
Salpetriere are seventy centimetres, and I have actually tried one of one
metre. It seems impossible to obtain good effects from small machines,
which cannot be used without a condenser, and which patients are
ordered to buy, with the injunction (too common an error) to treat them-
selves." My own experience would correspond closely to this. The
main object is to get a machine that you can rely on in all atmospheric
STATIC ELECTRICITY AND MAGNETISM. A-lll
conditions, giving a fair quantity of electricity at a sufficiently high
pressure or potential.
METHODS OF APPLICATION.
1. The Electric Bath, or Static Insulation.—The patient is placed on the insulated plat-
form, in communication with one of the poles of the machine,—say, the positive. After
some turns of the handle he is found to be charged with positive electricity of a high poten-
tiality, at the same time offering means of a constant waste of electricity from all parts of his
body and clothes,—waste which is continually repaired by the electricity flowing from the
conductor of the machine. The physiological and therapeutical effects of the electric bath
cannot be doubted. This is the base of all treatment by static electricity, and might even
constitute it entirely ; after at least a few sittings its action is purely sedative.
2. The Electric Souffle, or Wind.—This is obtained by directing the point of a metallic,
uninsulated rod toward the patient, at a distance of about a foot, by induction ; the point is
electrified negatively (that is, if we are using positive electricity) ; it communicates its
electricity to the adjacent air-molecules or dust-particles; they are thus attracted to the
nearest part of the patient's body, and we have a discharge by convection, by a stream of
particles producing an actual current in the air. The action of the souffle as a sedative is
most remarkable, and may be compared with the galvanic anode, but it is found to be more
energetic.
3. Sparks.—These are obtained by bringing a metal-ball electrode sufficiently near the
patient that the dielectric between the ball and the body is broken down ; they are used to
excite muscular contraction by acting on the muscle direct, or on the nerves supplying the
muscles, and to excite cutaneous sensibility.
■4. Aigrette.—This is produced by bringing a rather blunt metal point or a piece of wood
near the patient's body. We have no electric wind or spark, but an intermediate form of
discharge. When the point is positive it is a luminous brush of a bluish or violet color.
This form of application is especially useful in the treatment of* nervous patients, where we
wish to lead up to stronger applications, or where we want to act upon a sensitive surface,
as the face.
5. Electric Current.—This is effected by passing a metallic, uninsulated ball more
or less rapidly over the patient's clothing. It thus produces a multitude of little sparks,
whose length is measured by the thickness of the interposed fabrics. The friction brings
about a disagreeable or even a painful sensation,—smarting and burning. The skin is
reddened as by stinging. Some patients whose cutaneous sensibility is dull or perverted
find the friction agreeable. The reason why the friction can oniy be made over clothing is
evident; if the ball were applied to the skin there would be no insulation, as it simply con-
veys the electricity to the earth ; the friction, like the sparks, exercises a stimulating local
action and a distant and reflex action, whose effect, on the whole, is sedative; practiced
over a large surface of the body, it is distinctly stimulating. Friction made on the lower
half of the body diminishes spinal congestion, such as a spasmodic state of the lower limbs,
exaggerated reflexes, seminal emissions, etc. During the action of an electrical machine
ozone, or distinctly odorous gas, is developed in considerable quantities. The peculiar
smell which accompanies a flash of lightning is due to the transformation of atmospheric
oxygen into this gas. According to Dr. Lauder Brunton the passage of an electric spark
causes tRe molecule of oxygen to split up into single atoms, which do not, however, remain
apart, but immediately coalesce either with other single atoms to re-form molecules of
oxygen or with other molecules of oxygen containing two atoms to form a molecule of
ozone, which thus contains three atoms. To show the presence of ozone a piece of paper
impregnated with a solution of iodide of potassium is used ; if the gas is present the paper
will assume a deep-blue color. This gas can be administered in an effectual manner to the
patient by means of an insulated electrode consisting of a small disc carrying half a dozen
points. The electrode is held near the patient's open mouth (not within sparking distance),
and he is required to breathe deeply, thus inhaling the ozone. This is of great service in
asthma and anaemia.
A-112
McCLURE.
COMPARISON BETWEEN GALVANIC AND STATIC ELECTRICITY.
If we take an ordinary galvanic battery—say, of 20 cells—and com-
plete the circuit by means of a piece of fine platinum wire a few inches
in length, it is raised to a white heat. If we complete the circuit in an
induction machine by joining the poles by means of the same wire, no
effect whatever will be observed. In the latter case the quantity of elec-
tricity is too small to sensibly heat the wire. If the terminals of a gal-
vanic battery be two copper wires and the circuit completed by bringing
them together, a small spark will be seen when they touch, but the spark
is so short that it would be impossible to measure it, while with an elec-
tric machine of moderate size we would get a spark of several inches in
length. If we connect a Leyden jar by its two coatings to the poles of
an electrical machine and the handle is turned for some time, the jar will
either burst or overflow, if the machine is powerful enough : if not, a
strong spark will be obtained by connecting its inner and outer coatings.
If the ends of the Avires from the battery be now connected to the coat-
ings of the jar, it will be found that, however long the battery may be
left on, neither overflow nor spark will be produced. To charge a
Leyden jar we require not a large quantity of electricity, but a high
potential difference. The electrical machine gives a high potential dif-
ference, but a very small current; at the same time be it remembered
that static electricity can do all that can be done by galvanic or dynamic
electricity ; it has physiological as well as luminous and heating effects;
it can magnetize iron or steel and produce chemical changes. It is not
improbable that before long a static machine may be invented not only
giving a high voltage, but a large quantity of electricity ; the problem
to be solved is the lessening of resistance between the different parts of
the machine.
MAGNETISM.
An ordinary bar magnet exhibits certain familiar phenomena when
suspended by its centre of gravity; though free to turn in any direction,
it will invariably come to rest in one position,—that is, with its poles or
ends pointing north and south. The forces which turn the magnet into
this position, or maintain it there, are due to the action of some other
body, which may be a magnet. The space where a magnet experiences
this action is called a magnetic field. The earth produces a magnetic
field. The forces experienced by a magnet and due to the earth's mag-
netic field are sensibly the same at all parts of any space of moderate
dimensions, as a room. Within such a space the field is said to be
uniform, and the direction of the magnetic force is the direction which
the axis of a freely-suspended magnet would assume. When the axis
of the magnet does not coincide with that direction, two equal and oppo-
site parallel forces act on the magnet; these forces tend to turn the
STATIC ELECTRICITY AND MAGNETISM. A-113
magnet so as to bring the axis into the direction of the magnetic force.
The body producing the magnetic field experiences equal and opposite
forces, tending to turn it in the opposite direction. A magnet produces
a magnetic field in its neighborhood and modifies any magnetic field pre-
viously existing there. The field due to a magnet is not uniform ; the
forces may be much greater than those due to the earth. Magnetic fields
are also produced by electricity in motion. Under the undisturbed
action of the earth's magnetic field the end of the axis of any magnet
points in a direction which differs at different parts of the earth's sur-
face, but which is always northerly. If a magnet be broken into the
smallest particles possible, it will be found that each particle is a magnet
having two opposite poles, so that each particle possesses properties
exactly similar to a bar magnet. We may imagine a magnet to be com-
posed of molecules which cannot be further divided by physical means.
This include's Webber's theory. Ampere's theory, which is now gener-
ally accepted, supposes that each molecule of the magnet has a current
of electricity circulating round it. These currents are assumed to exist
in all magnetic substances ; before magnetization they move irregularly;
after magnetization they circulate in parallel directions. If the observer
face the north pole of the magnet, the currents move in an opposite direc-
tion to the hands of a watch, and, of course, looked at from the south pole,
they move in the same direction as the hands of a watch. So we see that
magnetism can be defined as electricity in rotatory or whirling motion.
An electro-magnet is simply a bar of soft iron, generally in the shape
of a horseshoe, round which a coil of insulated wire is wound, through
which a current of electricity can be passed. Electro-magnets are often
used to magnetize bars of steel, as they are much more powerful than
ordinary permanent magnets. We can magnetize by an electric current
in the following manner: By winding silk-covered copper wire in a coil,
attaching the ends to the terminals of a fairly strong Yoltaic battery;
move the coil from one end to the other of a bar (or a horseshoe-shaped
piece) of steel, taking care to move it always in one direction. We can
also magnetize by the earth's induction. If we take a poker and hold it
parallel to the direction of a freely-suspended magnetic needle, we
should expect that, if the poker were built up of magnetic molecules,
each molecule would try to set itself in a direction parallel to the sus-
pended needle; for we should suppose that the earth would act on the
.molecules of the poker as it does on the needle. The direction or dip
of a suspended magnet at this part of the world is almost vertical. So
we should hold the poker vertically. If we hold it thus for a few min-
utes and then test it for magnetism by trying whether either end of it has
the power of repelling either end of a suspended magnet, it will be found
that it has not acquired any sensible magnetic properties. Steel railings,
however, which have remained in a vertical position for many years, have
frequently been observed to have acquired magnetic properties, the lower
8
A-114
McCLURE.
end having become a north pole, as we should expect, if Webber's theory
be true. Now, as we know, all the molecules of the poker are closely
packed together, and it is therefore quite possible that the earth may
exert a force tending to set them in a definite direction, but that this
may not be strong enough to overcome the cohesion of the molecules.
If we could by some means diminish this cohesion, we might have better
results; this can be done by simply striking the poker with a hammer
when held in a vertical position, and it thus becomes a magnet, the lower
extremity becoming a nortti pole ; but if the poker be reversed and again
struck its magnetism will be immediately reversed also. The cohesion of
the molecules can also be diminished by heating the poker; when thus
treated and left to cool in the vertical position, it becomes a magnet.
A slight sound is heard when a body is magnetized or diamagnetized
by an electric current, and is due, according to this-theory, to the sudden
turning of the molecules. This production of sound during magnetiza-
tion was utilized in one of the earlier forms of telephone receivers. Heat
is also produced when a magnet is rapidly magnetized or diamagnetized.
We have seen that the space through which the influence of the
magnet extends is the magnetic field of such a magnet. This force in-
creases as we approach the poles and diminishes as we recede from them.
At every point it has a definite intensity depending upon the distance
from the poles; and it has a well-defined direction at every point, as
indicated by the line of force passing through the point. We can see
the general distribution of these lines of force by placing a sheet of
cardboard above a magnet resting upon a table; if we sprinkle iron
filings over the cardboard, and as the filings fall gently tap the card-
board, we can see that they arrange themselves along certain curves ;
these curves represent the lines of force.
Magnetic Induction.—A piece of iron, not of itself a magnet, will,
when placed in a magnetic field, become magnetized in the lines of the
magnetic force in the field. Thus a bar of iron, placed with its longest
axis in the direction of the lines of magnetic force, will become a bar
magnet, having its north pole at that end of the axis toward which a
north pole would, under the influence of the field, tend to move.
The action by which iron becomes magnetic in a magnetic field is
called magnetic induction. The molecules of iron in a magnetic body
before magnetization are, by Webber's theory, assumed to have their
axes turned in every possible direction, the magnetic actions of the
molecules thus neutralizing each other so that the body will not act as a
magnet. If the north pole of a bar magnet be brought near such a body
it will attract the unlike poles of the molecules and will repel the like
poles ; so that the molecules will tend to arrange themselves with their
north poles pointing one way and their south poles another way. The
molecules will thus act together, forming a magnet whose south pole
will be the pole next the north pole of the inducing magnet.
STATIC ELECTRICITY AND MAGNETISM. A-115
In a uniform magnetic field, iron magnetized by induction is not
impelled in any direction by the magnetic force, which acts with equal
and opposite force on the two induced poles. When the field is not
uniform, the induced poles, which are themselves equal, are unequally
acted upon, and motion tends to take place in the direction in which that
pole would be urged which lies in the stronger part of the field. Thus
iron, in virtue of the magnetism induced in it, is attracted by either pole
of the bar magnet; for the end of a piece of iron, say, near a north pole
will become a south pole and will be more attracted than the distant
north pole of the iron is repelled. A magnet shaped like a horse-
shoe having poles near the ends will attract a piece of soft iron placed
opposite and across the ends to the best advantage, for each induced pole
will be in the most intense part of the magnetic field which the magnet
can produce.
We see here, as in static electricity, that induction precedes attrac-
tion. Iron in which magnetism has been induced can, in its turn, induce
magnetism in another piece of iron.
Paramagnetism and Diamagnetism.—Other substances besides iron
and steel can be magnetized by induction, acquiring properties similar
to iron, but in a much feebler degree; these substances are called mag-
netic or paramagnetic to distinguish them from other substances, such
as bismuth, which also acquire polarity under the influence of a magnetic
field, but in which the direction of the induced magnetism is opposite to
that of the magnetic force. The latter substances are called diamagnetic.
One result of these two opposite arrangements of induced poles is
that all paramagnetic matter in a magnetic field tends to move from the
place of smaller to the place of greater intensity of force, and that all
diagnostic matter tends to move from the place of the stronger to the
place of the weaker intensity of magnetic force. Diamagnetic matter is
repelled, paramagnetic matter is attracted by the pole of a magnet; con-
sequently, while a bar of iron, if free to turn, tends under the action of
induction to place itself along the lines of magnetic force, a bar of dia-
magnetic matter, such as bismuth, tends to place itself across these lines.
All bodies are either paramagnetic or diamagnetic, but the magnetic
effects are much feebler with all known forms of matter than with iron
or steel.
The Earth's Magnetism.—The earth's magnetic field is not one which
could be produced by a simple bar magnet or any simple system of bar
magnets. The earth has not got a magnetic pole in the sense given to
the pole of the magnet. It is usual, however, to call these points on the
earth's surface where the direction of the lines of magnetic force is vertical
the magnetic poles. The magnetic pole situated near the northern end
of the earth's axis resembles what we have called the south pole of a bar
magnet; the earth's pole in the south resembles the north pole of a bar
magnet.
A-116
McCLURE.
Therapeutic Application of Magnets.—At the present time there is
no evidence of a reliable nature that a magnetic field, no matter how
powerful it may be, exerts any sensible influence on the healthy human
organism. In certain abnormal states of the nervous system, notably in
hysteria, effects of a remarkable character are produced; muscular con-
tractions are relieved and anaesthesia temporarily cured when a large
compound magnet is brought near the patient. This I have seen done at
Charcot's clinic at the Salpetriere, under the personal direction of Charcot
himself. And there is no doubt that in other hands, as well as in his,
they have been the means of even curing some neuroses.
At the Salpetriere at the present time, however, magnets in the treat-
ment of disease are little used, static electricity having almost entirely
superseded them. In the use of magnets as therapeutic agents the
phenomena are necessarily entirely of a subjective character, and are
therefore open to many objections, amongst them being the possibility of
such applications degenerating into charlatanry. Magnets are often of
service in diagnosis, indicating the presence and position of needles or
small pieces of steel or iron in the tissues, and are frequently a great aid
in the removal of such foreign bodies. The electro-magnet is the form
now generally used for such purposes.
THE FARADIC OR INDUCED CURRENT; ELECTRO-
MAGNETISM; ELECTRO-MASSAGE, AND
INSTRUMENTS.
By GEO. J. ENGELMAKN", M.D.,
ST. LOUIS.
I. HISTORY.
The induced or interrupted current is generally termed the faradaic,
or faradic, in commemoration of Faraday, to whom we owe the discovery
of this form of electricity, and also the induction coil of Ruhmkorff, as
a direct result of this discovery that an induced current of electricity is
generated in a conducting, or closed, wire circuit placed near to, but not
in contact with, another circuit through which a current is passing.
The history of faradic electricity, in its relation to medical science,
is a curious and unusual one; hardly had it been discovered, three-score
years ago, but its physiological and therapeutic properties were clearly
defined ; and it was not only at once accorded a place in medicine, but it
attained a preponderance and popularity now unknown. Much has since
been forgotten, and little has been added to our knowledge of this form
of electricity, notwithstanding the wonderful progress in other branches
of electrical and medical science.
In the early part of this century magneto-induction instruments of
crude form were used here and there, but they proved unsatisfactory: the
method of application was vague and general.
The first attempt at localized application, with a distinct object in
view, was made by Sarlandiere, in 1825, who sought to limit the effect
of electricity to certain muscles and nerves by guiding the current
directly to the part to be reached by means of needles, one connected
with either pole, and plunged into the tissue so as to concentrate the
current upon that part of the muscle or nerve between them. It is need-
less to say that the pain caused so far surpassed any possible benefit that
this method found little favor.
Oerstedt, of Copenhagen; Ampere, Schweigger, and others led the
way by their investigations to the development of this form of electricity,
produced by the induction coil as invented by Faraday, who, moreover,
in 1831 gave us the laws governing electro-motor induction, the induc-
tion of magnets on currents and of currents on currents, and showed
that we can increase the electro motor force by increasing the number
of windings of the conducting wire, as each winding or turn of wire cuts
across the lines of force independently. His electro-magnetic induction
experiments during the early thirties, led to the Ruhmkorff coil, which
(A-117)
A-I18
ENGELMANN.
has ever since served for the production of the faradic, induced, or in-
terrupted current in the laboratory, and, without the condenser, as the
type for all instruments employed in medicine.
Not one of the earlier instruments has survived, but we must record,
as among the first, the apparatus for the therapeutic use of voltaic in-
duction currents constructed in 1831 by Masson, and another invented
about the same time by Pixon, for the application of magneto-electric
currents.
It was not until the forties, after the investigations of Faraday and
the invention of Ruhmkorff, that more serviceable magneto- and volta-
electric instruments came into the hands of the practitioner so that this
form of electricity could be practically utilized. At first the rotary or
magneto-electric apparatus prevailed, but soon yielded to the more con-
venient volta- or galvano- electric instrument,—gradually disappearing
more and more, until at the present day it is known by name only, not-
withstanding some good points which should at least preserve it from
total oblivion.
The new instrument soon became popular, as it was small, easily
manipulated, and gave currents of great physiological energy; powerful
effects upon the nerve were felt, and upon the muscle seen as well as
felt, yet little was really accomplished ; the current was vaguely and
indiscriminately applied until Duchenne showed that it should be local-
ized to attain satisfactory curative results. Others as well seized upon
the new therapeutic agent,—men such as Marshall Hall and Golding
Bird in England, Froriep in Germany, and others; but it was Du-
chenne, known by the city in which he labored as Duchenne of Boulogne,
an accurate observer and careful experimenter, who, by his thorough
electro-physiological and neuro-pathological researches, at once firmly
established the induced current on a scientific basis; and we may well
speak of this great apostle of faradism as the founder of modern electro-
therapeutics. Enthusiast as he was, he practically excluded galvanism
from the field by confining his work to this one form of electricity ; and
he not alone discovered its physiological and therapeutic properties, but
developed and perfected them so that but little has been added since his
day. As an able contemporary truly says, he placed faradism almost
where it now stands,—far ahead of the present general knowledge. If
we follow the course of his investigations, from his first publication in
1847 to the final results as they appeared in his classic work, " l'Electrisa-
tion Localisee," in 1855, we shall review the more important physical,
physiological, and pathological features of faradic electricity.
Duchenne, guided by the idea suggested in the impracticable exper-
iments of Sarlandiere, sought to localize the current to certain parts or
organs, to confine and concentrate its effects upon nerve and muscle
without influencing the skin in its passage, or to concentrate its powers
upon this superficial structure without affecting the underlying tissues.
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-119
He applied the dry metallic electrode to the dry skin, and, although
sparks and crackling gave evidence to eye and ear of the passage of the
current, as did the superficial sensory nerves, no physiological phenomena
were produced, proving that it did not penetrate; the same current,
applied to the same points by means of sponge-electrodes, well moistened
in warm salt water, produced neither sparks nor crackling, but nerve-pain
or muscle-contraction, as it traversed sensory or motor nerves or muscles.
He also found that the muscle was contracted, not only by the current
directly traversing its fibre, but also, and even more effectively, by a
current penetrating at certain well-defined points, not necessarily near to
or directly upon the muscle. These points—which he called " points
d'election," points of choice—were proven, by Remak and von Ziemssen,
to be the points at which the motor nerve is nearest the surface and most
easily reached by the current, generally near where it enters the muscle.
This discovery led him to make the distinction, still upheld, between
direct muscular contraction, produced by placing an electrode upon the
muscle itself, and indirect contraction, produced by irritation of the
nerve controlling the muscle.
His thorough studies of the muscular system in health and disease
were followed by physiological and pathological experiments upon other
parts, and taught him, even then, the impotence, if not danger, of the
faradic current in disease of the central nervous system.
Furthermore, it may surprise some of the prolific writers of the
present day to know that Duchenne, as far back as the forties, recog-
nized the difference between coils of heavy and of fine wire,—one of the
most important features in faradic electricity,—which I have endeavored
to elaborate, and which has called forth the attack, the sarcasm, and con-
demnation of certain of the authors of modern works on electro-thera-
peutics. Though Duchenne made the distinction between primary and
secondary coils, finding that at times the current from the one, at times
that from the other, appeared the stronger, he did not clearly understand
that their individuality was due not to the difference in direction or in-
duction in primary and secondary coils, but to their quality, the length
and thickness of the wire forming the coil. He found that the action of
the secondary coil was more intense upon the skin, and of the primary
upon deep-lying organs, especially muscles, and speaks of an "electric "
action of the coils, yet recognizes that the difference depends upon
physical laws; although he himself could give no possible explanation
of this clearly-established fact, he denies that given by the physicist Bec-
querel, who claimed that the varying tension of the coils must account
for this difference in the effect of the current. ,
The discovery of the difference in the action of primary and sec-
ondary—in other words, of heavy and fine—coils was made by Duchenne
in the faradization of the bladder with one electrode in the rectum and
one in the bladder : finding some irritation of the sacral plexus in the use
A-120
ENGELMANN.
of the secondary, or fine-wire, coil he desired to weaken the current, and
inserted the primary, or heavy-wire, coil, which, contrary to his expecta-
tion, proved still stronger and caused intense suffering. Although un-
able to give an explanation, he clearly established the difference in the
character of the current from primary and secondary coils, making five
main points, to which I shall refer in the proper place.
Barring trifling errors, and the illusions of the enthusiast, as the
man must be who would succeed in any one sphere, the work of Duchenne
still stands, at the present day, as the foundation upon which every
method of localized electrization is based, and, I can but repeat, strange
as it may seem, far in advance of the present general knowledge.
The faradic current was received with general favor and over-
shadowed all other forms of electricity as a therapeutic agent; its pre-
ponderance being due to the thoroughness and the wide-spreading of
Duchenne's work, whilst novelty, cheapness, and simplicity at once made
it popular : it was more readily kept in order; there were fewer elements,
fewer connections ; it was seen, heard, and felt; doctor and patient knew,
by sparks and buzzing, by nerve-shocks and muscle-jerkings, when the
apparatus was at work, whilst the cumbersome and expensive galvanic
current, especially if properly used, gave no appreciable effect; the pa-
tient was not satisfied ; a slight burning, perhaps, but no shocks ; nothing
so startling or effective, as it would seem ; and the doctor, before the
days of the galvanometer, often in doubt whether his battery " was
working " or not.
Faradism was the one form of electricity used in medicine; the
scientific researches of du Bois-Reymond and Pfliiger, in 1850, upon the
electrical phenomena in living animal-tissue, were the first evidences of
recurring interest in galvanism. In their studies of the effect of the
anodal and cathodal opening and closing currents upon nerve and muscle,
which proved of such diagnostic import, the induced current played but
a secondary part; and when, in 1855, Robert Remak, of Berlin, disclosed
the merits of the constant current, which he looked upon as the only
practically-useful form of electricity, galvanism assumed a supremacy
which it has ever since retained,—in the main, I believe, because it ap-
peared of greater import and excited a more general interest as being the
form of electricity which first served industrial purposes.
Amid the triumph of galvanism the excellent work of Tripier, who,
in 1860, presented to the French Academy a sledge instrument con-
structed by Gaiffe, with a series of coils, both primary and secondary, of
varying length and thickness of wire, made no impression whatsoever,
receiving but passing notice even in his own home. His name to-day is
almost unknown, though the results of his labors are now appearing; he
demonstrated the varying therapeutic effects of currents' from differently-
constructed secondary coils, and devised the first instruments for bipolar
faradization of uterus, vagina, and bladder, which have recently been
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-121
elaborated and have guided Apostoli to his valuable methods of bipolar
faradization.
The enthusiastic teachings of Remak excited renewed interest in
electricity ; " as witli each.important discovery men's minds turned anew
to this strange agent extravagant hopes were again aroused, only again
to be followed by failures ; " so that, when the recoil came, and a calm
survey of results actually accomplished followed the first enthusiastic
laudations, the current almost fell into disrepute, as practically useless
and but the agent of quackery. During my student days, in the very
home of Remak, I was taught that it was without effect for therapeutic
purposes, though of diagnostic value in some obscure nervous diseases.
Yet from time to time a fresh impetus was given by some new theory,
experiment, or discovery, and popular favor was ever readily extended
to this mystic and wonderful agent from which so much was expected.
During all these therapeutic fluctuations scientific investigation con-
tinued, and wonderful progress was made in the practical application of
electricity; medical thought and experiment naturally turned in the
same direction, and profited by the results evolved.
A more thorough knowledge of the properties of electricity, the
introduction of the polar method,—above all, of measurement and dosage,
as first applied by Apostoli in 1884,—made the constant current more
tractable and serviceable, and again a great wave of electro-therapeutics
swept over the profession, all to the credit of galvanism, crowding out
faradic electricity more and more. The persistent efforts of Rockwell
have given general faradization a place, as the American method, in
therapeutics ; Apostoli has perfected and practically applied the methods
of bipolar faradization, first indicated by Tripier; whilst my own efforts
toward increasing range and efficiency of the current, by variation and
increase of interruption and by gradation of coils, however successful,
have altered the general situation but little as yet.
Yaluable additions have been made to our knowledge of faradic
electricity in recent years by scientific investigators, prominent among
whom are de Watteville, with his investigations on electrical tension, in
1877; Gaertner, who studied the electrical resistance of the human body,
in 1887 ; and Kraiewitsch, who taught the application of Ohm's law to
induction currents, in 1889 ; Stauffer, on the quantity of induced currents,
in 1890; then Weil, on fine- and heavy- wire spools, in 1891 ; and, lastly,
d'Arsonval, the brilliant Frenchman, who has probably done more than
any investigator now living to further our knowledge of the physiological
effects of the faradic current.
A bar to the progress of faradism is the impossibility of satisfactory
therapeutic measurement; although the physical quantity of induced
currents can be determined with precision, the measurements so far
achieved are no gauge of physiological effect, and even the fundamental
laws of electricity fail in certain phases of this current. It can be meas-
A-122
ENGELMANN.
ured in micro-coulombs and volts, and milliamperes can be determined;
yet this in no way indicates physiological efficiency, as character and
frequency of interruption and resistance and character of coil may alter
these without varying the physical qualities indicated by the measuring-
instrument. The quantity of electricity remains the same, however much
the curve—which is indicative of physiological effect—may vary. Never-
theless, some attempts have been made at direct measurement: a faradim-
eter was recently promised by an able and enthusiastic American author,
whose efforts have so far, it would seem, not been successful. The only
instrument which has appeared is the faradimeter of Edeknann, which
indicates, by a scale on the slide, the strength of the current from that
one coil in volts on short circuit, and for a motive power of 300 milliam-
peres ; yet it is no more indicative of physiological effect than a scale
marked at pleasure in inches or centimetres. It is a beginning, though
incomplete and, I must even add, misleading as a physiological or thera-
peutic measure.
It may be interesting to sketch, in a few words, the development
and present status of the apparatus which furnishes the induction cur-
rent for medical purposes, and I am sorry to say that it well demonstrates
that no progress has been made for decades since the completion of the
galvano-faradic instrument, when it displaced the earliest forms of the
magneto-induction apparatus.
Any instrument of the present day, of whatever make, on either side
of the Atlantic, is perfect in one way ; " it works well," is well made,
extremely satisfactory forthe price,and can be had in suitable shape for any
purpose the practitioner may desire, as pocket, box, or stationary battery.
But whilst all instruments now made function well and " buzz " smoothly,
the great majority furnish but one form of current, thus greatly impairing
their utility, and to this fact mainly is due the secondary position occu-
pied by the faradic current, as well as its limited therapeutic use. The
average instrument of the day is not equal to that of Duchenne, with its
efficient primary, or coarse-coil, current, and is inferior to the one con-
structed by Tripier, in 1860, with its series of coils and variability of
interruption. Some few makers, appreciative of the wants of the profes-
sion, are now furnishing superior instruments, which admit of the
application of the widely-different forms of the faradic current, so essen-
tial to its efficient therapeutic application ; greater range is being given
to the coil and to the rate of interruption ; in fact, greatly improved
instruments have quite recently appeared.
Present Status of Faradic Electricity.
The preponderance given to galvanism by the labors of Remak still
prevails, and has of late been strengthened by the striking effects of
electrolysis, by the perfection of the polar method, and the possibility
of measurement and dosage; the efforts of individual workers in the
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-123
field of faradic electricity availing but little to improve its status. Gal-
vanism is in fashion, and fashion is a power in medicine. The faradic
box is stowed away, its use is to a great extent confined to those who
still deem one form of electricity as good as another, or choose their
instrument for its cheapness,—a curious state of affairs in this progressive
age, due to lack of interest on the part of manufacturer and electrician,
scientist and practitioner, to the inferior character of the average instru-
ment, and to ignorance of the physical and physiological properties of
the induced current, which is a terra incognita to the majority of those
who use electricity in medicine, and even but little explored by the more
advanced ; yet light is dawning, more perfect instruments are being-
furnished, and scientific investigation is perfecting our limited knowledge
of this neglected form of electricity.
A brief review of assertions made in even the most recent text-books
and publications by prominent writers will at once reveal the vagueness
and uncertainty of present knowledge in this sphere, and may serve to
explain the distrust and disregard of the practitioner for this form of
electricity :—
In the International Electrical Congress, held in Frankfurt in 1891, one of the questions
under consideration was "whether therapeutic results can be achieved by the current
which can not be achieved by suggestion," and much stress was laid on suggestion as a
main factor in electrical treatment, prominent in the effects claimed for static electricity,
though less so in faradic and galvanic applications. Another speaker expressed the opinion
that, in the use of the faradic current, the irritating action (reizende Wirkuug) alone is
directly or indirectly serviceable in treatment; the sedative, nerve-quieting, effect he did not
mention. Th* Edelmann faradimeter, which is not by any means, as was intended, a
therapeutic meter or measure of faradic electricity, he recommended for the laboratory or for
the specialist, though too complicated and expensive for the practitioner, and, in citing the
instruments necessary for therapeutic purposes, " der kleine Spanner," one of the small-
sized faradic boxes, without variation of coils or interruptions, is recommended as answering
all demands ; and for purposes of measure, dosage, and comparison the number of inter-
ruptions and size of electrode are named ; yet no means of determining or of varying the
number of interruptions is given, and the main features, character, and position of coils and
resistance of body are ignored.
The Edelmann faradimeter, here quietly accepted as a measure of faradism, is another
evidence of the darkness still enshrouding this current; it has been accepted because it
emanates from one of the most competent and scientific of electricians, with the assistance
of a prominent electro-therapeutist, and is presented by them to the profession as the first
instrument for the measurement of the induction current, which is to remove that stum-
bling-block to the progress of faradism,—the absence of measure. And what does this
instrument accomplish ? It records the voltage of the current in short circuit, i.e, as
measured directly, unimpaired by any obstacle, without body resistance, and is hence merely
a deceptive snare for physiological or therapeutic purposes, as the tissues permeated, or
character and extent of resistance, which is here ignored, vary the current value in the
most surprising manner; for instance, the heavy coil, when in perfect juxtaposition, gives
a current of 240 volts by the Edelmann faradimeter, and yet this has but an imperceptible
physiological effect when applied through a high body resistance ; whilst the fine coil, which,
in the same position, indicates only 180 volts, has a powerful effect, and, on the contrary,
when applied through a low resistance, as in visceral or bipolar faradization, the intensity
and efficiency of the 240-volt current far exceeds that of the 130 volts.
The strength of the current would be far better approximated by indicating the nature
A-124
ENGELMANN.
of the coil and the resistance offered than by the volt scale of this faradimeter; yet it Is a
beginning, and a move in the right direction, not to be confounded with the faradimeter
pictured in an American work, to which I should not again refer were it not to exemplify
how lightly this subject of faradic electricity has been treated. The following statements
are calmly made of an instrument which does not, and did not then, exist: " With this at
our command we can observe and record qualities, tension, and volume of the faradic cur-
rent used upon a patient in terms of the 6ame standard, the volt, and the ampere." As the
instrument has not materialized it is needless to call attention to the fact that the coulomb,
and not the volt and the ampere, is the electrical unit by which we must measure faradic
electricity; and that, as I have already stated, even this is no index of its physiological
effect.
Most authors have nothing whatever to say of the tension or quality of the inter-
rupted current, and I refer to works which have appeared in the last few years; but one
text-book, on " Electricity in the Diseases of Women," does touch upon the subject, stating
that " the volt-force of the faradic current probably varies from several hundred to several
thousand volts," whilst, as a matter of fact, it rarely attains the intensity of several hundred:
the volt-force of a shorter coil varies from 10 to 300 volts, with an inducing current of 300
milliamperes and 2% volts ; and that of a fine coil from 5 to 180 volts, as Edelmann states.1
Hardly more definite are the teachings in our medical works upon other features of
faradism. Thus, the subject of current-break, the essential,"the very life of this form of
electricity, receives but little, if any, attention. One author passes it over with the injunc-
tion " to avoid an instrument which makes a harsh noise," and another limits his demands
upon the interrupter to " a clear note " as important in gynaecological practice. The varia-
tion in the physiological effect of the current by change of interruption, and the complete
control exercised over it by a properly-adapted trembler, which I claim to be a prominent
feature, has never been alluded to.
When variation of interruption is spoken of, it is within limits which afford no positive
alteration of physiological effect, and a definite assertion is never made, the number of in-
terruptions necessary to obtain a certain effect is never given, and no instrument exists in
which a definite number of interruptions as needed for & definite purpose can be obtained at
will. Rapid and slow interruption is occasionally spoken of, but the reader is left to infer
the meaning of these words ; but one author, the most scientific, tells the practitioner how
to determine the number of oscillations of the trembler by comparison of its sound or note
with that of a tuning-fork of known vibration. Yet this knowledge, acquired with such
difficulties, is of little value, as it will be almost impossible to again obtain this same
number of interruptions, and practically it is of no importance, as the range of possible
variation is insufficient for the obtaining of practical results thereby. A single instrument
exists, now in the College of Physicians, in Philadelphia, devised and described by Onimus
and Le Gros, in which the rapidity of interruption, within moderate limits, can be defined,
but it has never been particularly utilized. I will add that, since writing this, attention
has been directed to this point, and efforts in this direction have been made by some of the
leading workers.
More detrimental to the therapeutic progress of faradism has been
the persistent ignoring of the variable physiological effects produced by
currents from coils of varying resistance and electro-motive force or
different length and thickness of wire: one author, regardless of what
was already taught by Duchenne half a century ago, tells us that "all
usable strength and qualities of a faradic current are obtainable from a
single secondary coil," and even speaks of the " coarse-wire nonsense "
11 note these measurements as recorded by Edelmann, and yet I have my doubts as to their
accuracy ; my own measurements are not as yet completed, and I prefer to give no imperfect
data, but will only say this much, that I find higher amperage from the heavy coil, and, as far as
I can now say, lower voltage ; hence I wish it distinctly understood that I am here quoting from
Edelmann, and giving the voltage as impressed on his faradimeter.
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-125
as something to be eradicated because it is absurd and confusing to the
practitioner. I have myself been thoroughly scored for venturing to
insist upon the variability of therapeutic effect produced by coils varying
in their relations of resistance to electro-motive force, or coils of fine and
heavy wire, and, in short, in a comparison of recent medical literature,
we are confronted by vague and contradictory statements, mainly theo-
retical, without a sound physical, physiological, or therapeutic foundation.
Thus, quality and therapeutic effect are estimated by the feel of a current
to the hand or arm of the investigator. It is upon such grounds
(Steavenson and Lewis Jones," Medical Electricity,"London, 1892) that
the identity of currents from coarse and fine coils is asserted ; and upon
similar experiments is founded the statements of Edelmann, that static,
faradic, and galvanic currents, with like interruption and like force, are
identical, which would be true, provided that change of potential, volt,
and ampere force were similar,—an impossibility from the very nature
of these currents ; but, because a single impulse from an approximatively
similar faradic and galvanic current cannot be distinguished by the
healthy tissues of a blindfolded observer, we cannot assert identity of
quality and therapeutic effects. Let such reasoning cease. Feel is no
indication of quality or effect; the feel of the mustard plaster and the
same-sized plate electrode with a proper galvanic current is not to be
distinguished, nor is that of the slowly-heating cautery point and the
galvanic needle, the heated metal and the galvanic plate electrode. And
yet, is the character of the agent and the effect produced one and the
same ?
Even the electrician or the physicist adds to the existing confusion
when he seeks to arrange electro-physiological and electro-therapeutic
facts in harmony with the elementary laws of electro-physics, unconscious
of the fact that the human body does not react like a bar of iron or a
coil of wire; that measurement in electrical units is not a measure of
physiological effect; that a current of high tension and great quantity
may have a minimal physiological effect, whilst a current of low tension
and small quantity may act with the greatest intensity; and that even
Ohm's law ceases to hold good upon the human body when currents are
interrupted with sufficient rapidity.
We can hardly wonder at this unfavorable condition of affairs when
every idea of quality and quantity is wanting; when even the effect of
the current is doubted or but vaguely acknowledged ; when its effect is
judged by the/eeZ it gives to the hands of the investigator (Steavenson,
Edelmann, and others) ; when it is questioned whether the effect of the
current is not mainly suggestive or psychogenic (Electrical Congress,
Frankfurt, 1891) ; when an irritating effect alone is ascribed to faradic
electricity (idem), or its effect is strictly limited to "conditions which
exhibit nerve- or muscle-weakness " (Massey),—in itself by no means
a narrow or unimportant field; when the average small faradic box is
A-126
ENGELMANN.
advocated as answering all purposes (Frankfurt Congress); and when
the choice of a faradic apparatus is deemed of little consequence, and the
details, such as character of secondary coil, " can safely be left to the
judgment of the manufacturer," and " the clear note of the spring inter-
rupter" is cited as the one mechanical detail which requires looking into.
A solution of these complicated questions, and an understanding of
the intricate phases of faradic electricity, can be obtained only by scien-
tific research, by physical, physiological, and therapeutic experimenta-
tion ; indeed, the progressive work of individual investigation is now
beginning to lift the veil, yet obstacles of various kinds bar the way to
the development of faradic electricity as a satisfactory therapeutic agent:
we are under the sway of galvanism, and the recently-introduced alternat-
ing current, like all novelties, is detracting from the longer-known
forms of electricity; so that we can but trust to the energetic work of
those interested in faradic electricity, and to the perception of the pro-
fession, that they overcome these influences and accord the proper place
to the interrupted current.
It is not a question of the respective merits of these various forms of
electricity, as each has its own especial sphere ; and that of faradism,
though it can never supplant galvanism, is far broader and more im-
portant than the profession now take it to be, and that of the alternating
current must yet be determined.
II. INDUCED CURRENTS.
Every change, be it of force or position, in a magnetic or galvanic
field, gives rise to a current of electricity in a conducting circuit near to,
but not in contact with, such field. Currents so produced are called in-
duced currents ; they are, as ordinarily developed (unless the change in
the inducing force is of infinite rapidity), subject, like other currents, to
the law of Ohm, and are gauged by one or the other of the standard
units of electrical measure.
Induction currents are of short duration, persisting only during the
persistence of the change in the magnetic or galvanic field, the change in
the inductor or inducer: and, as their existence is dependent upon a change
of force or position, and their intensity co-ordinate with the rapidity
or intensity of this change, the potential never for an instant retains
its primitive value; it is constantly changing, and never attains a per-
manency.
A. Kinds of Induced Currents.
In accordance with the kind of force and change in the inducing
field we distinguish between magneto-induction currents and galvano-
or volta- induction currents.
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-127
I. MAGNETO-INDUCTION CURRENTS.
The magneto-induction current is developed by a change of position
between inducer and induced, between a magnet and a closed circuit, the
latter being the secondary coil to the ends of which the rheophores are at-
tached. This is accomplished by rapidly approaching and again remov-
ing the induction coil from the magnet, or, as it was more commonly
done, by a rapid revolution of the magnet, thus approaching and re-
moving it from the coil, each motion generating a current, but in oppo-
site direction to the other. The strength of this current increases with
the strength of the magnet, the rapidity of movement, the number of
windings in the .secondary coil, and the approximation of the coil to the
magnet. This was the principle upon which the earlier rotary, or mag-
neto-electric, instruments were constructed ; but as this current is no
longer used in medical practice, and, moreover, presents the same general
features as the galvano-induction current, we will not elaborate it.
II. THE GALVANO-INDUCTION CURRENT.
The galvano-induction current is developed within a neighboring
secondary circuit by a variation in the flow of force in the galvanic field :
one current is generated by the increase, and another, in opposite direc-
tion, by the decrease, in the flow of force. This current increases in
strength with the strength of the generating galvanic current in the
primary circuit, with the number of windings or lines of force in the
secondary circuit, and with the approximation of these circuits,—of the
inducing force to the induction coil,—but also with the brusqueness of
the change in the flow of force.l
The theorist knows, and the practitioner to his regret may have
discovered, how greatly variation influences even the direct galvanic
current. Whilst a continuous current of 200 milliamperes may be applied
without pain in gynaecological treatment, when slowly increased to that
intensity, rapid increase is very painful, and sudden making or breaking
would be almost unbearable. The indirect or induced current, however,
owes its very existence to variation of force, and is greatly intensified by
the brusqueness of that variation, which reaches its climax in the sudden
making and breaking of the current.
As the physiological effect of the current induced in the secondary
circuit is proportionate to the rapidity of the variation, or the intensity
of the change, in the flow of galvanic force in the primary or inducing
circuit, we obtain the rpost effective induction current by the most rapid
and extreme change of force in the inductor; that is, by the sudden
change from 0 to the full current-force, and again by the fall from its
highest efficiency to 0,—that is, by the instantaneous making and break-
ing of the current. Gentle variations of the galvanic flow in the inductor
1 This is true as regards the physiological properties of the current, and to a certain extent
as regards its physical properties, although these are not co-ordinate.
A-128
ENGELMANN.
do not produce induction currents which affect muscle or nerve, but it is
the brusque, sudden change which does achieve the physiological effect.
III. WHY THE GALVANO-INDUCTION CURRENT IS PREFERABLE.
The effect of the induction current being due to variability of status,
the highest efficiency can never be achieved by magneto-electric currents,
produced by a change of the relative position of magnet and coil, Vhich
can only be progressive, approximative, but never instantaneous ; hence,
for practical purposes, the galvano-induction current is used, but its
efficiency is increased by the plus of a magneto-induction current pro-
duced not by actual approach and removal of a magnet, but by the more
effective sudden magnetizing and demagnetizing of a soft-iron core,
within the coil of the primary circuit, by the making and breaking of the
inducing current: thus, two currents are induced in the neighboring
circuit or secondary coil. It is known that if an inducing circuit is
traversed by one current and another is induced at the same time, its
effect is increased thereby "if this current is of equal polarity or in the
same direction, and diminished if in contrary direction : thus, the mag-
neto-induction serves to strengthen the volta-induction current. The
current developed by the making of the galvanic flow—the make or
closing current—is contemporary and equipolar with that produced by
the approach or make of the magnet,—the current of magnetization,—as
the break or opening current is identical with that of demagnetization ;
hence, the resulting induction is as the united product of the two forces.
B. Medical Currents.
I. FUNDAMENTAL LAWS.
For a more thorough understanding of the current as applied in
medicine we must recall the fundamental principles of faradic electricity.
The establishment, variation, or cessation of a current produces polariz-
ing effects in a neighboring circuit, as proven by the passing current if
this circuit is a parallel wire, or by the magnetizing effect if it is a bsu*
of iron, at right angles; and vice versa, variation, relative or absolute,
of a magnet causes currents in neighboring circuits, wdiose direction,
intensity, and duration are in direct relation to the direction, intensity,
and duration of the change in the magnetic inducing phenomena.
A current which is established or approximated causes a current in
opposite direction in the neighboring circuit: a current which ceases, is
removed, or passes away causes in the neighboring circuit a current or
a polarity of the same sense or direction as the one in the inductor.
These induction phenomena all depend upon a variability in the inductor,
either of condition or position ; they cease as soon as permanency is
established, in either form of change. Direct induction currents are
those produced by the negative variations, cessation, opening, or re-.
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-129
moval, and are in the same sense or direction as the current or polarity of
the inductor. Inverse currents are those developed by a positive varia-
tion, by establishment, increase, or approach, and are in opposite direc-
tion to the inductor.
Self-induction.—Any variation in the flow of force in a circuit
develops a current within its own conductor, and this product of self-
induction, the extra-current, is in contrary direction to the producing
current, and weakens it. The extra-current of make or close is inverse
to the current proper of the circuit, or indirect; that of opening or
break is in the same direction as the inducing current, or direct.
Direction.—If an observer be swimming in the magnetic field in the
direction of the lines of force, which enter at his feet, the current pro-
duced by a variation passes from his right to his left. The direction of
a current induced in a circuit by any variation in the flow of force is
such that it, at every moment, opposes the movement which produces it:
if the flow increase,—approach of the magnet or making of the current,
—the induced current opposes its increase and existence; that is, it is in
the opposite direction to the current which produces it: if the flow
decrease,—removal of magnet or breaking of current,—the induced
current opposes the diminution, i.e., it is in the same direction as the
inducing current.
The duration of the induced current is equal to the duration of the
variation in the flow of force which produces it.
The quantity of electricity is equal to the variation in the flow of
force (independent of its duration") divided by the resistance of the
circuit.
II. DESCRIPTION.
We can, then, picture the medical current as follows: a galvanic
field, consisting of a loop of wire as primary circuit, through which a
current is passing from a battery, B, and surrounding this, but not in
contact with it, a turn of wire, C", as secondary circuit. A steady cur-
rent now flows through C from P to N, which is without effect on C";
let the wire be broken at I, and no current can pass; but if the contact
is suddenly made, the circuit, C, completed by uniting the wires at I, an
induction current is produced in C", at the making of the current in C,
in contrary direction to the primary flow of this force, and this again
induces an extra-current co-ordinate with itself in C; so that we now
have in C the battery current, weakened by the opposing extra-current;
but let the flow of force through C continue steadily without change of
potential, all induction effects will cease as completely as if no current
permeated the inducing circuit. If, now, the current in the primary
circuit is broken by disconnecting the wire at I, the potential is reduced
and another current is established in C" ; this is in the same direction as
the inducing current, and, reacting upon C, establishes an extra-current
9
A-130
ENGELMANN.
in the primary circuit, which is in the same direction as the original bat-
tery current. The current in C, both at making and breaking, is in one
and the same direction,—the primary is always a direct current in the
same direction, of the same polarity with the inducer,—while that in C"
Fig. 1.—Simple Primary (C) and Secondary (C") Circuit at Break or Opening
of Current.
alternates: at making of'the current it is in an opposite direction to the
inducing current and the current in C, an inverse current, and at break-
ing in the same direction with it, or direct. The flow of galvanic force
is feeble, and the magnetic force produced by a single circular turn or
wind of wire is small; hence, to increase this force, a number of turns
Fig. 2.—Lines of Force Increased by Turns of Wire, Forming a Solenoid
Current as Found on Closing or Making of Circuit.
are employed for the primary circuit, C (Fig. 2); these are made by the
winding of copper wire over a cylinder, and a solenoid is thus formed.
The induction force of the secondary circuit is likewise augmented by
an increase of the number of lines of force in the concentric superimposed
secondary coil.
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-131
If we regard the solenoid of the primary circuit as a magnet, as it
actually is upon closing of the current at I, its polarity will be such,
N—S, that the current induced in C" opposes its increase and existence
by its contrary direction, whilst with the breaking of the current this
magnetic polarity momentarily disappears, to be at once re-established
in the same direction by influence of the current established in C" by
the break in the primary flow ; the break current as opposing the move-
ment of diminution or demagnetization must be one of make or magneti-
zation ; hence in the same direction as the original galvanic flow. It
appears from this that the currents induced in two conaxial solenoids
at making of the current, and making or approach of the magnet, are
such that the current in the secondary coil is in contrary direction to
the one in the primary, while the secondary current of break and de-
magnetization is equipolar with it (in the same direction as the pri-
mary). Other conditions unchanged, the induction effect is increased
by an increase in the change of potential in the inducing circuit,—i.e.,
in rise and fall of the magnetic force in the primary coil, which can
be attained, without increase in battery force, by placing a bar of soft
iron within this coil. The lines of force in this solenoid may be
likened to those of a long, thin magnet; and if an iron rod is placed
within its axis, the lines of force will pass through this rod and mag-
netize it, and, on account of the greater conductibility of soft iron for
lines of magnetic force, they will be concentrated therein, and more
lines will then pass through the solenoid than if the iron were not
there ; practically we utilize a bar of soft iron within the primary circuit,
and thus develop more lines of force in the space around the solenoid;
we create a more intense magnetic field, and heighten its efficiency. This
core, by its successive magnetization and demagnetization, on make and
break of current, acts as an inductor upon the two surrounding conaxial
circuits, and acts in the same sense as the primary galvanic current.
Moreover, it serves, in the simpler forms of apparatus, alternately as
magnet and neutral body to an iron spring-head, which causes the open-
ing and closing of the battery circuit, thus acting as an automatic inter-
rupter, by means of which the most effective and physiologically active
induction currents are obtained from the primary galvanic flow: the
variability in the flow of force, which produces the induced current,
thus attaining its limit, as the most abrupt increase and decrease of cur-
rent and approach and removal of magnet is obtained by the sudden
making and breaking of current and magnetizing and demagnetizing of
core and solenoid.
The fluctuation of force in the primary circuit acts not only upon
the neighboring secondarv coil, but reacts upon itself (self-inducing),—a
reaction which is greatly augmented by the increase in the magnetic
powers of the circuit by the core of soft iron. These currents, resulting
from self-induction, are called extra-currents, and, from the laws enounced,
A-132
ENGELMANN.
it is evident that the extra-current of make, or magnetization, is opposed
to the primary current of make, and weakens it so much that it may be
disregarded, whilst that of break, or demagnetization, is co-ordinate with
the battery current, and is as a plus to the flow of force in the primary
coil at break ; hence, although make and break currents in the primary
coil are both direct, in the same direction as the battery current, the
latter preponderate to such an extent that we take account only of the
current of break and demagnetization.
The induction currents proper, in the secondary coil, are quite dif-
ferent in character; the inverse current, induced by closing of circuit
and make of the magnet, takes effect as well as the direct current of
opening and demagnetization. Although these currents are alternating,
in opposite direction, it is customary to attribute one direction, or
polarity, to them, which is always that of the fj"
current of break, or demagnetization, as its in-
tensity and physiological effect is far greater than
c
Fig. 3.—Faradic Apparatus, showing Current of Make and Magnetization.
that of the make current, though equal as to quantity. The curve of the
direct or opening current is more brusque, the variable stage to which
it owes existence being more brief than that producing the make current;
hence its greater physiological efficiency. We now have this condition
of affairs (Fig. 3) : 1. A galvanic current sweeps around the primary
coil, C, which (a) converts the core into a magnet, N-S, and (b) induces
a momentary reverse current in the secondary coil, C". 2. The sudden
magnetizing of the core itself induces a reverse current in the secondary
coil, which strengthens the galvanic induced current within this circuit.
3. The magnetized core attracts the soft-iron head of the spring to itself,
and so breaks the current-flow. 4. This stopping of the current-flow
stops the magnetizing influence upon the core, and a direct current is
induced in the secondary coil by the breaking of the primary current,
strengthened by that induced by the demagnetization of the core. 5.
The magnetic force holding the hammer being removed, it returns, by
the tension of the spring, from the core to the battery-wire, whereupon
another current passes, and by these vibrations the process is repeated
in such rapidity as the strength of spring and magnet admits.
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-133
III. CHARACTERISTICS.
Static
The faradic current, although the product of induction, is an electric
flow with all the properties of the electric fluid, which vary in degree
only in three forms in which it is employed in medicine, as galvanic,
static, and faradic electricity, and we may now add,
as a fourth, the alternating current. The faradic, which
resembles the lately-introduced alternating current,
being, as it were, an intermediate between galvanic and
static, is characterized by the brusqueness of its curve,
and by its variability, interruption, and alternation, as
compared to the constant and continuous galvanic, with
less quantity or ampere force than this, and higher
amperage, though less voltage, than the static. The
galvanic current, as used in medicine, has great quantity
with low voltage,—from 1 to 300 milliamperes, with
from 2 to 40 volts ; the faradic has less amperage and
higher voltage,—T^„ to T\j milliampere, with from 10 to
250 volts. The static has a minimal quantity, not over
To"o"oto"o"o" ampere, or xo'oo" milliampere, and the highest
voltage, from the hundreds upward. The alternating
current is used by Apostoli with from 32 to 64 volts.
These conditions may be graphically demonstrated by
the flat, voluminous curve of the galvanic current, the
abrupt, brusque curve of the faradic, and the still more
abrupt ascent of the static. Yet the properties of the
fluid in these various forms of its application remain
unchanged as those of
water, whether flowing in
the broad channel of a
stream, hurled in jets
from the nozzle of a
hose, or escaping as steam from the valves of a boiler.
The curve of the primary current differs greatly from that of the
secondary, as it differs in measure, sensation, and physiological effect;
sense or direction, duration and intensity of both currents is well repre-
sented by Fig. 5 (Edelmann), which shows us the primary flow, M N,
alternately made and broken every second ; a b,b c, c d indicate the
duration each one second, whilst af,bg,ch represent the intensities of
primary (battery) flow.
On make or closing of the current, at the beginning of the second a b
the primary flow is inauguarated, attains the intensity a f, at which it con-
tinues until the opening or break at the close of the second b, whe* it sud-
denly sinks to 0. To this current are added the extra-currents of the
primary circuit, on make, at a, an extra-current in a contrary sense, reducing
Galvanic
Fig. 4.—Current Curves.
A-134
ENGELMANN.
the force of the original flow at/, and at b, break, in the same sense thus
strengthening the flow at g. This make and break of the primary flow
induces the contemporary current impulses A, B, C, D, in the secondary
circuit; the less-powerful impulse, or current of make, A, C, being in a
contrary sense to the primary flow, whilst the break current, B, D, which
practically is alone to be considered, is in the same direction.
The primary flow continues whilst contact persists, but the second-
ary lasts only as long as the change of force in the primary flow on
make and break, and its intensity is proportionate to the intensity of
the primary as influenced by its extra-currents at the moment of make
and break.
In speaking of the faradic current it is virtually the opening cur-
rent, the current of break and demagnetization, which alone is consid-
ered, as it is the preponderating element in both primary and .secondary
coil, and determines polarity or direction, as well as intensity, of the
FlG. 5.—SliCO^DARY AND PRIMARY CURRENTS. (EDELMANN.)
currents. In the primary circuit the closing current is reduced by the
induced extra-current, which is in the same direction as the opening cur-
rent, and aids it so that the opening current is the sum of the induced
electro-motor force, and that of the inducing circuit itself, with a greater
quantity of electricity, as indicated by the galvanometer, and with
greater physiological effect. For the secondary coil the galvanometric
quantity of electricity, as measured on short circuit, is the same for both
opening and closing current; but as the physiological effect of the former
is greater, it is the opening current alone which is considered ; this is of
shorter duration, and, the same energy being expended in a shorter time,
is of higher tension, and its effect on muscle and nerve is greater; it is
the controlling factor, as far as physiological and therapeutic purposes
are concerned, and is alone considered, to the exclusion of the make or
closing current.
The opening current is formed and completed in about 0.000275
second, and the closing current in 0.000485 second, the ratio of potential
being as 6 to 13 for a current of this character. The duration of the
current*of opening is shorter, its curve more brusque ; its tension and
power to overcome the body resistance encountered in all therapeutic
applications is greater, and this preponderance over the closing current
FARADIC CURRENT, MAGNETISM. MASSAGE, ETC. A-135
increases with the increase of resistance. With large moist electrodes,
or in the electric bath, the physiological effect of opening and closing
current is the same : this is with lowest resistance, as we see also the
identity of physical effect in the sway of the galvanometer needle when
resistance is 0. As resistance increases, the preponderance of the
opening current steadily increases, until with the highest possible resist-
ance, as in the high-tension, single-wire current, we cease to see any
effect from the closing current, whilst that of the opening current is
marked. So in physiological effect, and the same is true of the high-
tension current in physical effects, a flash lights up the electric
lamp on opening, whilst no result is visible on closing. With more
moderate resistance the deflection of the galvanometer needle proves
to the eye this preponderance which the sense of feel readily discovers.
The resistance of the body varies with the tension of the current, being
less as the tension increases, less for the faradic current than for the
galvanic, and varying likewise for the faradic itself; less for the fine coil
than for the coarse coil, and less for the current of opening than for that
of closing; only when the body resistance is reduced to a minimum do
we find an equality of physiological effect in the currents, but this is a
condition rarely attained in medical usage, with the exception of the
faradic bath. The more brusque curve of the opening current is well
demonstrated by the spark, which is larger on opening than it is on clos-
ing of the circuit, although produced by the same amount of electricity ;
the same energy is expended in a shorter time, and produces a greater
effect. This spark, which serves no purpose but to convey the extra-
current of opening to the primary coil, consumes a large percentage of
the current-energy, of which some 25 per cent, is lost, much of this
being converted into heat in the spark.
The actual current-energy is indicated by I X E, or the current-
intensity multiplied by the electro-motor force,—the number of windings
in the coil (always remembering that E is actually E—E', as we shall
see later); in the secondary current it is only three-fourths of that in
the primary. Like opening and closing current, so anode and cathode
vary in physiological effect: the cathode, or negative pole of the faradic
current, has a greater effect on motor and sensory nerves, and can always
be recognized thereby. The closing contraction will be first observed at
the cathode, the opening contraction at the anode. Weak currents con-
tract only at closing in both directions Of the current; moderate cur-
rents show a stronger closing than opening contraction, and very strong
currents contract only at opening with ascending currents, and at closing
with descending currents. The effect of the poles on sensory nerves is
similar : whilst the closing contraction may be said to be cathodic and
the opening contraction anodic, both poles have a certain sensory influ-
ence but the closure (cathodic) excitation is greater than the opening
(anodic) excitation.
A-136
ENGELMANN.
The difference in the effect of the poles, like that of opening and
closing current, increases with the resistance, and here also we see the
most striking difference in the high-tension single-wire current, a bright
glow being obtained from the negative pole, with the positive grounded ;
but if the 118-volt lamp is connected with the positive pole, and the
negative is grounded, the light is more dim and intermittent or flashy.
Coils of high electro-motor force are necessary for these experiments.
IV. VARIATIONS.
The faradic current is a most pliable and variable form of electricity,
subject to changes (a) in intensity and quantity and (6) in quality, by
alteration in the current-giving apparatus and in the method of applica-
tion, thus making it possible to obtain a variability of physical and
physiological effects and giving it great therapeutic possibilities.
(a) Variations in the strength of the current are of two kinds, either
in physiological effect not measurable, or in quantity, as indicated alike
by measure and effect. The first, obtained by insertion or withdrawal
of the tube of Duchenne, by variation in the rapidity of the contact-
breaker and by variation of resistance, I will not here discuss, as it is of
little importance compared to the last, the now universally-adopted sledge
movement of the secondary coil. The tube is used only in small pocket-
instruments, and, while varying the shape of the curve, does not alter its
size, a diminution of intensity being accompanied by a corresponding-
increase in the time of the discharge, and vice versa; so that the product,
Q, or quantity, which is always equal to I X T, remains unchanged.
Change of resistance varies the effect of the current and its quantity in
a given manner, being inversely proportionate to I; yet the rheostat
would be an unnecessary addition and unsatisfactory for measuring pur-
poses, and the influence of varying body-resistance upon the faradic
current is hardly to be considered as a means of varying the current-
effect. Surface-resistance, determined by character of electrodes as well,
and also the number of interruptions, vary the strength of the current,
but they likewise vary its quality, and should rather be considered under
that head. As the influence of the interrupter as a controller or influ-
encer of current-strength is an entirely new feature, I will briefly outline
this method.
The current-strength, or rather its physiological effect, is gradually
though slightly increased by an increase in the rapidity of interruption
up to a certain speed of the contact-breaker, and then diminished by
increase in the rapidity of interruption. We see this exemplified by Coil
III, short, 1458 winds, 79 ohms resistance, as follows: with high resist-
ance, small metal electrodes to upper and lower arm, the first sensation
on single impulse is not experienced until 45 of the scale ; whilst a slow
beat, 150 per minute, is felt at 40^, and the more-rapid interruption, 4000
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-137
per minute, is already felt at 34. Muscle-jerk is obtained at 63 on single
impulse, at 52 with slow interruption, and at 43^ with rapid. The
greater the current-strength, the greater the number of interruptions
necessary to reduce the current to 0, or to annul its effect on the sensory
nerves ; but before this point is reached the muscle ceases to respond, a
rapidly-interrupted current, to which the muscle no longer reacts, still
influencing the sensory fibre.
A moderate current, such as that from Coil III of the Engelmann
battery (W. & B.), at 45 of the scale (or £), is sufficient to produce mus-
cular contractions with 45 to 1000 interruptions per minute. This
current grows stronger with an increase in the rapidity of interruption
up to 4000 per minute, then soon decreases,—muscular contractions cease;
at 6500 sensory nerves almost cease to react,—a current effect is barely
perceptible; and before 10,000 is reached it ceases to be felt altogether. If
the current is a strong one, as it is from the fine Coil III completely over-
lapping the primary, with an inducing force of 4 Leclanche cells, and
applied through large, moist electrodes, a current too strong for ordinary
therapeutic applications, the number of interruptions necessary to reduce
its physiological effect to 0 must be greatly increased ; but if pushed to
28,000 per minute, even this strong current will not be felt, whilst at
25,000 it is still perceptible. The rapidity of interruption controls the
physiological effect of the current as perfectly as the sledge movement
of the secondary coil; so that, all other conditions unchanged, it is an
index of current-strength, and might be used as such with well-regulated
interrupters.
To demonstrate this current gradation by variation in the number
of interruptions I will cite a single experiment. Coils I and III of the
Engelmann battery are used, with an inducing force of 300 milliamperes
and 5 volts (on short circuit, about 75 and 60 volts, respectively, by
single impulse), applied by moist electrodes, three by four inches, to
upper and lower arm, giving a moderate resistance (3000 ohms), which
almost determines equality of coils :—
NUMBER OF Coil I. Coil III.
INTERRUPTIONS PER MINUTE. FIRST SENSATION. FIRST DISTINCT MUSCLE-CONTRACTION. FIRST SENSATION. FIRST DISTINCT MUSCLE-CONTRACTION.
Position of Coil on Sledge Scale, in Millimetres, from Point of First Contact.
1600 3500 6500 11000 13200 5 10 15 20 27 15 20 25 30 35 5 15 25 27 32 22 26 ::o 34 35
A-138
ENGELMANN.
Whilst not actually applicable for purposes of measurement, this
table will serve to show the importance of the contact-breaker and the
necessity of noting the number of interruptions if any distinct idea of
current-strength is to be obtained, and it is self-evident that, for the
regulation of current-intensity, the type of apparatus hitherto in general
use must yield to more perfect and accurately-constructed instruments
which admit of a regulating and recording of the interruptions.
Variations in the quantity of the induced current, comparable to the
galvanometric measure or value, are obtained by the sliding of the
secondary coil over the primary. This is the method in general use
for the regulation of current-intensity. Its mechanism is simple; the
current-strength is readily seen by the position of the coil, and noted by
the scale marked on the sledge. The electro-motor force is indicated
with approximate precision by the arbitrary divisions of that scale,
as it is nearly proportionate to the distance between the centres of
the coils. This method of varying the current-strength has been
long since adopted, and has served for record by the placing of a
scale on the slide; and we can now appreciate its advantages over
other methods more fully, since we know that this change of position
indicates a change of force which is measurable, and that its galvano-
metric measure corresponds more nearly with the physiological efficiency
of the current than do changes of other kinds.
(b) Variations in Quality.—Of the greatest importance to the medi-
cal man are the variations in quality and physiological effect of the cur-
rent; so much so that I may say that upon this factor depends the ther-
apeutic value of the induction current. These current-changes, by which
the most varied therapeutic results can be obtained, are produced by
variation in the secondary coil, in the rapidity of the contact-breaker,
and in the extent of surface-resistance. Whilst the current-strength is
likewise varied more or less thereby, this is of minor consequence, and,
as we have in the sledge a method superior in every way to attain this
end, I shall consider only the essential feature, variation of physiologi-
cal effect or quality. Each element is characterized by an individuality
of action, and must be separately described ; and yet, in proper combina-
tion only is its highest efficiency and the greatest variability of physio-
logical effect obtained. Thus, the short secondary coil of heavy wire is
characterized by its effect upon muscle, especially the muscular fibre of
internal parts, where the resistance is reduced to a minimum ; but this
is by no means true under all conditions and for all purposes, and to
attain its greatest efficiency in this direction the coil must be combined
with low surface-resistance and slow interruption of the primary flow.
The long coil of fine wire is characterized by a sedative and anaesthetiz-
ing effect, but this is only with diminution of surface-resistance and great
rapidity of interruption ; with moderate interruption and high surface-
resistance its action is quite to the contrary,—revulsive. Whilst great
FARADIC CURRENT, MAGNETISM. MASSAGE, ETC. A-139
rapidity of interruption determines a nerve-quieting effect of the current,
this is only true of currents from long, fine coils, and applied with low
surface-resistance ; thus, we must utilize the different means of varying
the current-quality to attain the most perfect results, yet each acts
independently of the other and in a manner peculiar to itself.
The secondary coil greatly influences the physiological effect of the
induction current by variation in length and thickness of the wire used
in its construction,—that is, variation of resistance and number of winds,
—upon which quantity and electro-motor force, or tension, of the cur-
rent depend. These are the features which influence its characteristics
most decidedly, and not whether it be from primary or secondary coil,
as Duchenne supposed, who observed the effect correctly, but was misled
in his reasoning. We now know that effects which he obtained from the
primary coil, and naturally attributed to it, were due mainly to the char-
acter of that circuit, and are very similar to those produced from a sec-
ondary coil of similar character, and that the apparently peculiar effects of
the secondary coil are due mainly to the fact that this was always con-
structed of longer and finer wire. The distinction he makes between
primary and secondary coils holds good if we consider the primary as a
short, heavy, and the secondary as a long, fine coil; hence we have little
need of the primary circuit, since we can obtain the same variation of
effect more satisfactorily by placing a similar coil in the secondary
circuit.
Unquestionably there are some differences of physiological effect
between primary and secondary coils, but these are not of sufficient im-
portance for therapeutic purposes as long as we have only the one small
primary coil. Until we can obtain a greater range of primary coils, such
as I have in connection with a specially-constructed instrument, it is
far better that we confine ourselves to the secondary circuits, which
admit of comparison and of extensive variation.
The primary circuit, if properly constructed, has a special therapeutic
field, from which I have already obtained admirable results; .but I am
not yet prepared to discuss them, and they are unattainable from ordi-
narv faradic primaries; hence I will not dwell upon these currents.
From Duchenne's own statement we see that primary and secondary are
practically coarse and fine wire, or low and high, electro-motive-force
currents. The five main points of difference between primary (coarse)
and secondary (fine) coils made by Duchenne are: 1. The current from
the secondary (fine) coil acts more intensely on the retina, if applied with
moist electrodes to face or eyeball. 2. The secondary (fine) coil affects
the sensibility of the skin more intensely. 3. The primary (coarse) coil
affects organs more or less deep under the skin more intensely. 4. The
secondary (fine) coil produces more marked reflex contractions. 5. If
moist electrodes are used on the skin, the secondary (fine) coil penetrates
deeper than the primary (coarse).
A-140
ENGELMANN.
I have considered only the striking variations of current as produced
by changes in the secondary coil. Upon length and diameter of the wire
depends the resistance of the coil and the quantity of the current; the
number of windings or turns determine the electro-motor force; hence
these details must all be given in defining character and effect of a cur-
rent, and every coil should be accordingly marked. A short coil of
heavy wire is indicative of great quantity or amperage, and low tension
or electro-motor force; a long coil of fine wire, of small quantity and
high tension ; each factor has its significance, and it is a mistake to give
all importance to the number of turns of wire, or lines of force, as some
have done, claiming that a coil of heavy and one of fine wire will have
the same effect, provided that the number of windings are the same in
each, basing this assertion on the " feel " of the current and the idea of
an equality of lines of force, without physical or physiological experi-
ment, and forgetful of the important element of resistance, as varied by
thickness of wire. As a matter of fact, the current from two such coils
differs in quantity and quality, in galvanometric measure and in physio-
logical effect,—yes, even very much in feel. Let us examine two coils :—
Heavy : No. 15 wire= 0.85 ohm resistance, 528 windings.
Fine : No. 40 wire = 180.00 ohms resistance, 528 windings.
The heavy coil preponderates in quantity, or amperage; the fine in ten-
sion, or voltage. At 100 of the sledge scale, the coils overlapping, the
heavy coil gives, on short circuit, a galvanometric force of 25 milli-
amperes,and the fine coil only 0.5 milliampere, or one-fiftieth ; with 3000
interruptions per minute (high resistance, 50,000 ohms) and metal elec-
trodes applied to middle of upper and lower arm, the heavy coil causes
strong contractions, not at all painful at 100, perfect juxtaposition ;
whilst the fine coil could not be borne at that point of the scale, and is
very painful at 75, yet causing very slight contraction only, the heavy
coil producing strong contraction at 50, without any sensation. With
moist electrodes two inches square, in the same position, and a resist-
ance of 7000 ohms, the heavy coil causes powerful contractions at 70,
with almost no perceptible feel of the current; whilst the fine coil causes
strong contractions at 40, yet so painful that they cannot be borne
beyond 50. The current from the fine short coil, 528 winds, is an exceed-
ingly sharp one, affecting the sensory nerves, whilst the heavy coil affects
these but little, yet acts powerfully on muscle.
Surface-resistance, kind of electrode, and rapidity of interruption
greatly vary the current from coils of all kinds, affecting each one dif-
ferently, so that the effect of a coil cannot lie wholely defined without a
knowledge of the conditions under which it is used; yet, as a rule, I can
say that the short, coarse coil, low resistance, with greatest possible
electro-motive force, by prolonged application renders the parts more
sensitive ; even after & seance of ten minutes the current must be reduced
to avoid more powerful effects, whilst the current from the long, fine coil,
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-141
high resistance, and high electro-motive force, is sedative in its effect,
and quickly establishes a certain tolerance; this anaesthetic effect, in-
creasing with number of winds, thinness of wire, and rapidity of inter-
ruption. In a vagino-abdominal application for reduction of pelvic pain
the fine coil was distinctly felt at 35 volts, short circuit, with 3500 inter-
ruptions per minute, and after an application of five minutes was moved
farther over the primary to 50 volts before it was even felt.
With low resistance, as it is not generally met with in medical use,
though decidedly marked in the electric bath and in some bipolar appli-
cations, the current from the short, heavy coil is stronger and of greater
physiological effect than that from the fine coil; as the resistance in-
creases the fine coil gains ascendency, and with the high resistance usually
found it is stronger by far, with greater physiological effect, than the
coarse-coil current. Even in the spark we observe the marked difference
in effect; the spark from the shorter, heavier coil is shorter, but hotter,
from proper instruments giving sufficient heat to melt iron ; from the
long, fine coil it is longer, but gives less heat.
In a bipolar intra-vagihal treatment with an inducing force of 300
milliamperes and 1| volts, 2500 interruptions, the shorter coil, 2300
winds, No. 28 wire, produced painful sensations at 110 volts, short circuit;
whilst the longer coil, 8200 winds, No. 40 wire, was not even felt at 150
volts, i.e., in more perfect apposition with the primary. With 400 milli-
amperes inducing current, a heavy coil of 1100 winds, 3.8 ohms resist-
ance, and fine coil, 11,050 winds, 1030 ohms resistance, high circuit resist-
ance, faradic brush on elbow and hand, the fine coil is intense at 11 centi-
metres from complete juxtaposition, whilst the heavy coil is not even
painful when full in : but if large, moist electrodes are used, the coarse
coil at its weakest gives intense and painful contractions, whilst the fine,
full in, is painless and the contractions produced are but slight. The less
the resistance the less the preponderance of fine coil, until with minimal
resistance the coarse coil is strongest.
This weakening of the current is not due to a resistance measurable
in ohms, but to a counter-current produced by self-induction ; it is a
diminution of potential, and not an increase of resistance. The opening
current induces a counter-current in its own conductor, and thus prevents
the ascending; this counter-current does not change the quantity or the
galvanometric effect, and the surface of the curve remains the same at
the initial and maximum intensity, but its apex is very much changed.
This self-induced counter-current is stronger in the fine coil and stronger
with low resistance ; hence these peculiar phenomena. The law controll-
ing self-induction currents is this : that they increase in intensity (1) with
approach of the circuits, more intense the nearer the circuits, hence
greater in their own conductor than in a neighboring circuit; (2)
with diminution of diameter of the wire in the coils, hence greater
in the fine-wire coil; (3) with strengthening of the current, hence
A-142
ENGELMANN.
greater as resistance is less or battery force greater. By self-
induction the potential of a fine coil of 1030 ohms resistance through
a body-resistance of 3000 ohms is reduced to only 22 per cent, of its
original value, whilst that of the heavy coil is diminished much less,
remaining at 78 per cent, of its original value.
The electro-motor force cannot be measured simply by the number of
winds (Weil), but it is E—E', E' being the electro-motor force of the
counter-current. According to the nature of the coils their relative strength
varies, but for the-average extremes of coarse and fine coil equality of
current effect at the same point of the sledge is obtained at a body-resistance
of from 1000 to 3000 ohms (see experiment, p. 137, showing almost equal
effect of coarse and fine coil with variable number of interruptions at
3000 ohms resistance); but with metallic resistance this equality of
current, as measured, is obtained at from 200 to 300 ohms (Weil); so that
we may see how greatly current effects are varied by changes in any of
the determining conditions, and it is evident that the variations of
current obtained by differences in the construction of the secondary
coil are of the greatest therapeutic importance, and must be recognized
by manufacturer and practitioner before efficient instruments and satis-
factory results are obtained.
Having found that the highest possible resistance with the lowest
possible electro-motor force produces the most painful, irritating currents,
and the lowest resistance with the highest electro-motor force the most
powerful muscle effect with the least pain, I have improved on the
former coarse coil of 0.8 ohm resistance and 528 winds by a coil of fine
wire in multiple, giving 6500 winds with 4.1 ohms resistance, and thus
obtain the best contractile effects. The most useful coils for general
nerve and penetrating effects are with 4000 to 6000 winds, but sedative
effects superior to those from such coils I have obtained from coils of
9600 and even 12,900 winds, with resistance up to 2500 ohms. Experi-
ment, has shown me the peculiar physiological effects of the differently-
constructed coils, and 1 hope soon to be able to determine precisely and
accurately the conditions for various coils, under which they are most
efficient for their especial therapeutic purposes.
Rapidity of interruption likewise varies the quality and physiologi-
cal effect of the current greatly without altering the galvanometric
value. The effect of the contact-breaker is such that the strongest cur-
rents from the fine coil, in complete juxtaposition, with moist electrodes,
can be reduced from a maximum intensity, insupportable to the sensory
nerves, to 0, and with such regularity of gradation that the number of
interruptions may serve as measure of current-strength. Yet I utilize
the interrupter merely for the variation of quality or kind of effect;
slow interruption, from 5 to 200 or 300 per minute, determining more
effective muscular action, whilst the sedative effect upon sensory nerves
is more readily secured by rapid interruption,—20,000 to 50,000 per
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-143
minute. A current which, with moderate rapidity of interruption, pro-
duces powerful muscle-contraction with marked sensation is gradually
reduced as rapidity increases, the contractions cease, and it is scarcely felt
when the number of interruptions is increased still more ; finally it is com-
pletely obliterated, yet produces a sedative and even an anaesthetic effect,
though no longer recognized by the sensory nerves ; this anaesthetic
effect persists for a greater or less space of time, according to intensity
of current, rapidity of interruption, size of coil, and length of sitting.
Coil III, 32 wire, 6000 winds, 650 ohms resistance, at 45 of the scale, with
three by four inches moist electrodes and an inducing force of 4 Leclanche
cells, produces muscular contraction with 1000 interruptions per minute,
and is not felt with 7000, yet produces a sedative anaesthetic effect estab-
lishing tolerance ; at 100 of the scale, the coil full in, the current is too
powerful for motor or sensory nerves up to 15,000 interruptions, but
with 25,000 it is scarcely noticeable, and yet produces a decided sedative
effect. Rapidity of interruption, while strongly influencing the physio-
logical effect of the induced current, does not in itself control this as
completely as it does when combined with the proper quantity and quality
of current and surface-resistance ; that is, with suitable coil and electrode,
each in itself influencing the nature of the current in a similar manner
and approximating the same results.
In brief, I may say, of the contact-breaker, that the physiological
effect of the current slowly but distinctly increases with the number of
interruptions, from 1 up to 2500 or 3000 per minute; if the current be a
mild one, it reaches its highest intensity at 3000 to 4000, then decreases, at
about the same rate, until no longer felt with from 7000 to 9000 interrup-
tions. The muscles respond less acutely than do the nerves; very slow
interruption, of moderate current, is perceived by the sensory nerves
only; as rapidity increases muscular fibre contracts; with greatly-
increased rapidity the muscle ceases to respond, and finally the sensory
nerves; so that with great rapidity the current is no longer perceived,
and yet physiological effects are produced, though the current is not felt.
The greater the current strength, the greater the number of interruptions
necessary to completely annul its effect. Slow interruption favors
muscle-contraction and rapid interruption nerve effects ; the very rapid,
whether perceived or not by the sensory nerves, is sedative in its
action.
Surface-resistance, as produced by character and material of elec-
trodes and moisture or dryness of skin^ determines intensity, also quality
and effect, of the current, the latter being the important therapeutic
factor : moist electrodes, low surface-resistance, render the current pain-
less and penetrating without effect upon the superficial sensory nerves,
yet acting with energy upon deep-seated muscles; the cotton-covered
electrode, thoroughly saturated with fluid, reduces both surface- and
tissue- resistance; the dry epidermis is saturated, its conducting powers
A-144
ENGELMANN.
greatly increased, and its resistance reduced ; perfect contact is estab-
lished, the entire surface of the electrode is available, thus lessening the
density of the current to a minimum, rendering it painless and causing
it to penetrate; the same current, from the same coil, might be arrested
upon the surface with revulsive effect, causing great pain in the super-
ficial sensory nerves. This radical change in the physiological effect of
the current is produced by a diminution of surface-resistance, the highest
resistance, a painful surface-current, being produced by the dry metallic
electrode placed loosely upon the skin, the smoothest penetrating current
by the moist electrode pressed firmly against it.
A secondary coil of 32 wire, with 4500 feet, 747 ohms resistance, and
a current of 400 milliamperes, applied with high surface-resistance, small
metal electrodes, to the middle of upper and lower arm, 500 interrup-
tions per minute, is intensely painful at 50 of the scale, so much so that
it could not be borne stronger; applied in the same place with low
surface-resistance, by the moist electrodes, two inches square, even with
the utmost intensity of current, with coils overlapping, at 100, strong
contractions were produced, but no pain. The metal electrode with this
coil at 50, half in, powerfully affects the sensory nerves, motor nerves
barely responding, whilst the moist electrode is hardly perceived under
these conditions ; and if the current is increased by the moving forward of
the coil to 100, strong muscular contractions are produced, but still the
sensory nerves are little affected. Thus, it is eAudent that surface-resistance,
character of electrode, and method of application vary the physiologi-
cal effect of the current, as Duchenne has long since taught. A revulsive
effect is produced by high resistance, dry skin, and metallic electrode,
whilst the penetrating, deep nerve and muscle effects are from moist
electrodes, with low resistance; especially quality and physiological
effect is altered by variation of surface-resistance, quantity and galva-
nometric measure being less affected. The primary electro-motor force
unchanged, we vary the intensity of the induction current by the sledge
movement of the secondary coil, and its quality, or physiological effect,
by variations in the character of the secondary coil, in the number of
interruptions, and in the amount of surface-resistance, as determined by
character of electrodes, never relying upon any single one of these
factors, but combining these various methods of current-variation to
achieve the desired result.
V. MEASURE AND RECORD.
The absence of definite galvanometric measure is another of the
unfavorable conditions which have served to retard the therapeutic use
of faradism. As the study of the induction current by the galvanometer
affords no indication of its physiological action, and as up to the present
time we have no means of determining a unit of physiological efficiency,
we must content ourselves, for purposes of measure and of record, by
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-145
defining the conditions under which the current has been developed, and
the manner of its application.
It is impossible to compare satisfactorily currents from all medical
instruments, by reason of the great difference in construction, especially
those in which gradation is one of physiological effect only, without
change in any measurable quantity. Uniformity of record and a defini-
tion of current-strength can be attained only in the sledge instrument, in
which the galvanometer effect, like the physiological, decreases with the
removal of the secondary coil from the primary, and the extent of sepa-
ration of the coils is an approximate gradation; hence, I shall consider
only currents from instruments of this kind, which are in every way supe-
rior for medical purposes.
The measurable element in the induced current is its quantity; we
cannot properly speak of its intensity, nor can we value it in amperes ;
we can estimate only its quantity, the product of time and intensity
(Q = IXT), which is expressed in micro-coulombs and is measurable.
The same is true of the condenser discharge, as we may see by the ex-
periments of Edelmann, who finds a condenser discharge of 9.8 volts in
261 millionths of a second as effective, physiologically, as one of 70 volts
in 70 millionths of a second of time, the increase in time serving to
make 9 8 volts as effective as 70; but peculiar difficulties likewise oppose
the measurement of this form of electricity, as volt-force is lost when
passing off under low potential, the more being lost the lower the
potential.
The opening faradic current is measured by sending it into an electro-
dynamometer and noting the maximum deviation given by this impulse
to the needle, then comparing this with the discharge of a condenser of
one micro-farad capacity, charged to the potential of 1 volt, therefore
containing one micro-coulomb, which, upon my instrument, is 3.95 divi-
sions of the scale. To measure a given induction flow the shock of the
opening current, obtained by pressure upon the single-impulse key, is
conveyed to the electro-dynamometer, and the number of degrees obtained,
as marked by the greatest deviation of the needle, is divided by 3.95, the
product being the number of micro-coulombs, or the current quantity. We
can now indicate the galvanometric value, by noting the quantity of the
opening impulse in micro-coulombs upon the scale for every change of
position of the coil—this being true for a fixed inducing current—for
one given coil and for a certain resistance. Moreover, it is necessary
that every opening impulse be alike, which is possible only by an even-
working contact-breaker, as it is made, but not found in the average
instrument for the more-rapid interruptions.
The scale so graded as to indicate in micro-coulombs the quantity of
current for a certain resistance is, at present, our nearest approach to
measure ; and this resistance must be a body resistance, as the current-
energy varies differently for metallic and for body resistance ; the maxi-
10
A-146
ENGELMANN.
mum intensity for metallic resistance being attained at 0 or complete
overlapping of coils, and at 3 centimetres for body resistance. Even
with attention to these details this is deceptive and the scale only an
illusory one, as the physiological effect varies with conditions ever
present in therapeutic applications, which in no way affect quantity.
Granting that the inducing current remains unchanged, the physio-
logical effect varies with the resistance of the circuit and its variable
elements, these being the metallic resistance within the coils themselves
dependent upon length and thickness of wire, and the external resistance,
size and character of electrodes and body resistance proper, in itself
a most unstable element, varying for opening and closing current, vary-
ing for different points of the scale, and varying from one moment to the
other with the change of potential.
A single experiment will illustrate the extreme variation of current-
strength and effect caused by change of resistance, and also the variation
of that resistance by apparently trifling causes. Coil I, 0.85 ohm resist-
ance, 528 winds, with an inducing current of 400 milliamperes and 5
volts, applied by metallic electrodes, 2 centimetres in diameter, to right
shoulder and calf of left leg, with dry skin, presenting a body-resist-
ance of 50,000 ohms, is hardly felt at 100 or complete overlapping of
coils ; the electrodes are held in place by a spring, pressing them down
firmly ; the surface becomes red, congested, and moist, so that within ten
minutes, without change of any kind, leaving electrodes in place, the
current is distinctly felt at both anode and cathode at 47 of the scale,
less by over one-half, and is almost unbearable at 100, where but a few
moments ago it was barely perceptible. This remarkable change of
current effect is caused by reduction of surface-resistance, due to thin-
ning of the skin by compression, and its saturation with moisture by
perspiration through prevented evaporation and congestion of vessels.
If we now reduce the resistance still more, to 3000 ohms, and apply the
same current, through large moist electrodes, three by four inches, to
upper and lower arm, we find muscular contraction at 27 of the scale at
100 interruptions per minute, at 29 with 6000 interruptions, but no
sensation, and at 47 powerful contractions, without effect upon the
sensory nerves; and this coarse coil of 0.85 ohm resistance predominates
over the fine coil, 40 wire, 180 ohms resistance, 528 winds, which with
high resistance gave far the stronger current.
The experiment is instructive in many ways, but here cited especially
to demonstrate the variation of resistance within a few minutes, without
change of any kind by the operator, the electrodes even remaining in
precisely the same place. More striking still are the greater physioloo-i-
cal effects of currents of small quantity and low tension over currents of
great quantity and high tension : the latter from a fine coil of 6500 winds,
with a primary force of 300 milliamperes, 5 volts, 5000 interruptions, and
13 micro-coulombs of opening impulse, produced only a distinct jerk with
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-147
no disagreeable sensations, whilst the heavy coil, with 528 windings and
less than 4 micro-coulombs, produced strong and painful contractions.
This is with low resistance, under the less-frequent conditions of applica-
tion : the opposite effect would be observed were the test made with the
high resistance generally found in faradic treatment.
This striking result is due (Dubois, Stauffer) to the influence of the
extra- or self- induced current Of opening, within the secondary coil,
Fig. 6.—Edelmann Faradimeter.
upon its own coil-current. The self-induced current is, in opposite
direction to the current proper in its own circuit, more effective than the
current circulating in a neighboring circuit, and, being in opposite direc-
tion, it prolongs the variable stage of the original current which estab-
lishes it, prolongi/ig its duration at the expense of its tension, without
altering quantity or galvanometric measure; as these self-induction
effects increase with the number of windings and the thinness of
the wire, the co-efficient of self-induction is much higher for the fine
coil, and the current is counteracted far more than in the coarse coil,
A-148
ENGELMANN.
being practically 0 in Coil I (Engelmann), 0.8 ohm resistance ; hence its-
greater maximum intensity with less quantity and greater physiological
effect on nerve and muscle.
Even less indicative of physiological effect than the gradation of the
scale in micro-coulombs is that of the Edelmann faradimeter (Fig. 6) in
volts, which is only for a given coil, with a given inducing flow on short
circuit, but fails when body-resistance is interposed. The instrument
consists of two parts: the stand with the Grenet cells, C, B, and A,
with rheostat, W and D, and galvanometer, G, attached to the wall,
and the faradic apparatus some distance away, in order that the gal-
vanometer may be removed from the magnetic influence of the iron core
within the primary coil. The cell C supplies the motive power for the
current-interrupter independent of B and A, which give the current for
^Hf^DH1
Fig. 7.—Course of Current in Edelmann Faradimeter and in My Instrument,
with Separation of Coil and Interrupter.
P, battery for coil; I, coil; E, hammer-magnet; B, battery for hammer.
the coils; this primary current must be one of 300 milliamperes, in
order that the position of the secondary coil may always indicate the
correct volt-force of the secondary induction current, as marked on the
scale, R, of the sledge.
I use but one Grenet cell, and even this gives a stronger current
than necessary, but, by the nickelin-wire rheostat, W and D, through
which it passes, it may be reduced to the necessary intensity of 300
milliamperes, which is verified by the galvanometer, G, through which
the current may be sent at will by pressure on the spring-head, S,
now and then during the seance. The force of tlie primary flow is
controlled by testing the galvanometric effect.
Fig. 7 shows the current interrupted by a separate and distinct
vibrator as it is in the Edelmann faradimeter, in my new instrument,
and as it should be in every accurate instrument for medical work.
�26462
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-149
The cut (from Edelmann) likewise shows the hammer of Wagner-Neff
clearly as an individual feature, propelled by its own separate battery
power, whilst usually it is acted by the coil current. P is the battery
supplying the current for the coil, 7"; the circuit is closed at t and inter-
rupted at p and p by the hammer of Neff. The hammer, or trembler,
itself is operated by the battery, B, from which the current passes
through the electro-magnet, E, then to the anchor or bar of the trembler,
A, and the spring, y, which makes and breaks contact with the govern-
ing screw, k, the spring being set so that contact is established at p and
p when no current passes. As soon as a current is established by
closing the circuit by the key, S, the soft-iron horseshoe magnet, E, is
magnetized, acts as an electro-magnet, and attracts the bar, A, breaking
the current at p and p; the current broken, E is demagnetized and the
trembler, A, is released, returns, and re-establishes contact, thus making
and breaking the current at both points of contact, p and p, both for
the hammer current and the coil current; yet there is no current con-
nection between these two points, as the contact-breaker for the coil is
superimposed upon the bar of the trembler, A, but insulated from it, so
that the current from P—the coil current— is made and broken as often
as the trembler, A, completes a vibration, yet the currents are separated
by the insulating block. My own interrupter differs somewhat from this,
and my controllable high-speed contact-breaker is upon an altogether dif-
ferent principle, with this one point of resemblance only,—that the
motive power for coil and trembler is separate and distinct, whilst in all
other instruments now in use it is one and the same battery-force which
supplies both, and contact is made and broken by a spring alternately
attached to and flying back from the electro-magnetic coil core as it is
magnetized and demagnetized by the make and break of contact.
By the separation of the contact-breaker we avoid loss of power
and the self-induction action of the electro-magnet upon the coil current.
The quantity of the current is dependent upon (1) the galvanic
inducing flow and primary coil ; (2) number of winds of secondary coil
and thickness of wire, or coil-resistance; (3) position of coil on sledge;
(4) resistance of circuit, but in order to determine therapeutic or
physiological effect we must know (5) surface-resistance or character of
electrodes and skin ; (6) number of interruptions and time of applica-
tion. The only measure of effect we now have is a record of the details
of current production and method of application, and this enables us
to value the character, strength, and effect of the faradic current with
some degree of precision.
The following points I deem necessary for determination of current
effect and for record :—
1. Strength of galvanic inducing current.
2. Character of secondary coil, number of winds, and resistance of
coil.
A-150
ENGELMANN.
3. Resistance of the circuit, of body, and electrode.
4. Character and size of electrodes determining density of current,
pain, and penetrating power.
5. Position of secondary coil on the sledge scale.
6. Number of interruptions of the contact-breaker, approximatively
at least, until instruments of precision are furnished.
7. Duration of the seance, or time of application.
The first of these, the primary flow, is the only permanent one
of the various elements upon which the current effect depends; so
that it is evident how difficult it is to obtain a precise estimate of
current-energy or physiological effect, since quantity proper, as ex-
pressed in micro-coulombs, conveys only a partial and imperfect idea of
its value. But, in order to make even this record possible, it is necessary
that the manufacturer should construct the apparatus with precision,
and that each instrument should carry upon its face an index of force;
character of primary coil should be given, and each one of the series of
secondary coils must indicate number of winds and resistance of
wire; the number of interruptions of the variable contact-breaker, at
different points, must be marked ; and electrodes should be made in
standard sizes, and in proper relation to each other; uniformity in elec-
trodes, primary coil, and galvanic inducing flow would greatly facilitate
record and comparison.
VI. EFFECT; METHOD OF ACTION.
The effect of the faradic current upon the human system varies
greatly with the character of the current (force of primary flow, nature
of coils, and rapidity of interruption), the nature and size of electrodes,
and the resistance offered by the body itself; in general, I may say that
its action is-either irritating and stimulating or sedative, contracting or
relaxing, and that this effect of the current, upon any part or organ of
the body, is produced by its action upon the controlling nerves and
muscles ; but in what manner the effect is exercised I cannot positively
say. This is as yet an unexplored field. The mechanical action seems
prominent; whether or not it acts in other ways as well I am not pre-
pared to state with any degree of certainty. We know that the faradic
current can produce chemical changes, as is proven by the spark and its
action even upon the invulnerable platinum; but as the polarity is con-
stantly changing, the action of one current is counteracted by that of
the next, so that the effect can be but momentary, and nascent chemical
products rarely combine; so that a permanent effect can hardly be attained.
The chemical effects produced are greatest in currents of greatest
quantity from heavy, short, secondary coils, and of slow interruption,
becoming quite marked when the closing current is eliminated, as in the
one-direction current of the Stohrer instrument, and likewise in the
primary circuit. I do not believe that the chemical effect takes any part
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-151
in the action of the faradic current upon the system, but that this
is a certain mechanical influence upon the molecular composition of
the organism, prominent in its dynamic action (Stein). Boudet cured
facial neuralgia by the vibrations of a tuning-fork, 200 per second, com-
municated to a sounding-board, upon which was fixed a small rod with
ball end, which was placed upon the face at the point of exit of the
infra-orbital nerve, thus communicating the vibrations to that nerve;
after an application of from five to six minutes the pain ceased for a
time, and by continuation of the treatment a permanent cure was
achieved. I do not rely upon the one statement, but find this indication
of the curative therapeutic effect of mechanical vibrations corroborated
by the experience of others both in England and in France, and quite
recently Charcot's investigations have given a renewed impulse to
this medicine vibratoire: in the Salpetriere a large tuning-fork, placed
upon an extensive sounding-box, was used,-the atmospheric vibrations
produced thereby acting as did the rod in the other case, and with simi-
lar satisfactory results, even to the restoration of muscular activity in
the paralyzed lower arm of a hemianaesthetic.
I fully agree with Stein, who believes that in the mechanical vibratory
action of the faradic current we must seek the cause of its physiological
action ; but as to the idea expressed, that many electro-therapeutic effects
are due to a regulation of molecular vibrations, I can say nothing. The
question is still an open one, and must be solved ere faradism can be
accorded its proper place in medical therapeutics.
C. Medical Uses.
Faradic electricity is used in medicine for purposes (1) of diagnosis
and (2) of treatment, but the range of its utility has been limited by
reason of the prevalence of galvanism, our limited knowledge of faradism,
the absence of measure and means of comparison, and largely by the
crudeness of the instruments furnished, which give but a certain form of
induction current, to which therapeutic applications must, of course, be
confined, making it really useful in a comparatively small number of
cases only. It is impossible to compare galvanic and faradic currents
as therapeutic agents, as each has its proper sphere, and that of the in-
duced current will be greatly enlarged with increased knowledge and
greater precision and variation of current.
We speak of the positive pole as the anode and the negative as
the cathode, which may always be recognized by its sharper current
and greater effect on motor and sensory nerves. The prevalence
of the negative over the positive pole is more marked for short, heavy
coils than for long, fine coils, and likewise more marked when applied
through low resistance than through high resistance. Using Coil I,1
1 In speaking of Coil I, II, or III, I always refer to the standard coils of my apparatus as
manufactured by Waite & Bartlett, because these are the only coils which are precise as to
quantity and quality; number of winds, resistance, length and diameter of wire being noted.
A-152 engelmann.
with low resistance, 2500 ohms, both hands in warm zinc-water, 4000
interruptions per minute, the negative pole is first felt at 25 of the
scale and the positive at 31 ; the first contraction is secured by the nega-
tive at 44 and by the positive at 50. With Coil III, 1500 feet, and the
same conditions, the first sensation is observed at 12 at the negative
pole and at 21 at the positive, the first contraction at the negative pole at
26 and at the positive at 31. If we take a high resistance, though only
5400 ohms, we find less difference in positive and negative for Coil I, and
with Coil III, 1500 feet, the negative pole is first felt at 22 and the posi-
tive at 23, the first contraction or muscle-jerk, for both positive and
negative, being noted at 31, whilst for Coil III, 4500 feet, positive and
negative vary even less.
I. DIAGNOSTIC USES.
The faradic current is valuable diagnostically for determining the
existence, the increase or decrease of pathological excitability, in differ-
entiating between central and peripheral lesions, and in the detection
of simulation. In gynaecological practice it is of prominent diagnostic
import in differentiating between abdominal and more especially ovarian
pains of an hysterical and those of an inflammatory character. The
fine coil or tension current with its sedative influence has a potent
calming effect on hysterical suffering, especially in abdominal and ovarian
regions, and serves an admirable purpose in differentiating between
nervous or hysterical pains of the ovary and those which are inflam-
matory ; this means of differentiation, recently emphasized by Apostoli,
should be more frequently resorted to, as many a patient is subjected to
operation for ovarian pain of a purely hysterical nature, which would
have been detected and relieved by the faradic current, had it been prop-
erly tested.
In faradic exploration a careful comparison must be made between
the healthy and diseased side, or, what is less advantageous, between the
part in the diseased and the same part in a healthy person, and repeated
investigations are necessary before a positive result can be reached.
For scientific exploration we must know the resistance of the tissues on
either side, size and resistance of electrodes, number of interruptions,
and character of coil and current-strength,—which we are as yet unable
to give, but which, for purposes of record and comparison in one and the
same case, the primary-battery flow remaining unchanged, is indicated
by the relative position of the coil on the sledge scale. The irritability
of the muscle is tested by determining the lowest power of the faradic
current which will contract it, and then comparing this with the healthy
side. It may be noted that in hysterical paralysis electro-contractility
is generally normal while electro-sensibility is lowered, and in infantile
paralysis voluntary contractility is increased whilst faradic contractility
disappears; so also in the reaction of degeneration, or when by an injury,
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-153
a cut severing its continuity, the nerve is destroyed, and more or less
atrophy or degeneration is found in both muscle and nerve. Even with
the crude instruments of former days the variability of reaction in
healthy and diseased tissues was well characterized and the faradic cur-
rent a valuable diagnostic agent; so that we may now expect still more
from this current, so thoroughly controllable as it is by the new apparatus.
II. THERAPEUTIC USES.
Even in the secondary position still occupied by faradism it has
a broad range of application in medicine and is used in a variety of ways:
(a) applied to the body direct; (b) in faradic massage; (c) in the faradic
bath.
(a) The direct application of the current, with both poles in contact
with the body, is the usual method of therapeutic use of induction cur-
rents, as general, as localized or polar, and as bipolar faradization.
General Faradization.—The labile application, over the entire sur-
face of the body, so earnestly advocated by Rockwell, is used as tonic
and stimulant in constitutional debility; above all, in nerve-exhaustion,
and as a powerful irritant in cases of asphyxia, suspended animation, and
poisoning.
Localized faradization, as Duchenne termed this new departure in
electro-therapeutics, the application of the current by one pole direct to
the part to be affected, is the method most generally used, and should
more correctly be spoken of as polar faradization, in contradistinction
to the bipolar method and the polar method of galvanization, which is
precisely the same manner of application in the use of the galvanic cur-
rent. This localized or polar method of application has done away with
the former distinction between ascending and descending currents ; but
we still speak of labile and stabile currents, one of the electrodes being
moved over the surface, or both stationary, and of superficial and deep,
or penetrating, currents,—the former with the dry metallic electrode to
the dry skin and superficial nerves, the latter with moist electrodes to the
deep-seated tissues. These are the ordinary methods of its therapeutic
use : as nerve and muscle irritants in all kinds of paralyses, heart-weakness
from various forms of poison,as stimulant in cases of constipation, vesical
weakness or relaxation of nerve- or muscle- fibre in any part, and as seda-
tive in neuralgias, in hysterical and inflammatory pains ; the short coil
of fine wire serving as the most powerful irritant with the dry electrode,
the long coil of fine wire having the greatest penetrating power, and with
very rapid interruption of current the most marked sedative effect,
readily producing tolerance and a certain amount of anaesthesia. The
short coil of heavy wire, with slow interruption, produces the most
effective muscular contractions, but, instead of producing tolerance,
seems to render the tissues more susceptible.
The Bipolar Method.—The bipolar method is the localization of the
A-154 Engelmann.
current by means of a single electrode carrying both poles, and has of late
assumed prominence by reason of the able and energetic work of Apostoli
and the efficiency of the methods devised by him in uterine and pelvic dis-
ease. It is restricted almost wholly in use to the inner parts, the cavities
and mucous membranes, and is practically the application of localized elec-
trization to internal organs ; since the current, to be localized or confined
to these parts, must of necessity be applied by means of a single elec-
trode; as so little space is given, a metallic rheophore only is admissible,
and this can be used effectively for penetrating currents on the mucous
membranes, which offer a very low resistance, not to be compared to that
of the dry skin, and for this reason, as well as the absence of the
numerous sensory nerves, it causes much less pain than would a metallic
electrode upon the skin,—indeed, no pain at all. Currents of quantity
for muscle effects, and currents of tension as nerve stimulant or sedative,
can both be used to advantage, and without causing pain.
Our knowledge of faradic electricity and the means of varying and
of applying the current have improved so that the principle long upheld,
that for external faradization currents of tension are most active and
that in internal, bipolar or localized, faradization the current of quantity
acts most vigorously, can no longer be followed as a fundamental rule.
Although it is true that currents of high tension penetrate deeper where
the resistance is great, as upon the skin, and that the current of quantity
is strongest if the resistance is very low, yet it is wrong to generalize
and to refer the current of tension to external and the current of quantity
to internal faradization. Some of the best therapeutic effects of tension
currents, such as the relief of ovarian and pelvic pains, are achieved by
their internal use, and equally striking results of quantity, or coarse-coil
currents, are obtained in external application, as for purposes of massage
or direct muscular contraction.
The advantages claimed by Apostoli for the bipolar method in
internal applications are (1) that it is more simple, requiring no assistant;
(2) that it is less painful, the sensitive skin being avoided ; (3) that it is
more active, as localizing the full effect of the current used upon one
small part; (4) that it is more efficient, as it admits of the use of stronger
currents by reason of the lessened sensibility.
(b) Faradic Massage.—Under this term, which I look upon as a mis-
nomer as it is now used, is generally understood the combination of faradi-
zation with massage : the heightening of the stimulating or sedative effect
of massage by a corresponding faradic current applied by means of the same
apparatus by which the mechanical effect is exercised upon the tissues, be
it hand, or plate, or roller electrode. This I should call a combination of
massage and faradization, whilst I term faradic massage proper the
stimulating or contracting of the muscle by faradic currents of quantity
and slow interruption,—the most efficient of all means of muscular stim-
ulation or massage, as it can be applied directly to any desired muscle
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-155
or group of muscles, and stimulates the tissues by arousing heightened
natural action.
I will not elaborate this now, but will speak merely of faradic
massage as generally understood, a most agreeable and effective method
of treatment. The effect of massage, which has been established in our
country by the earnest efforts of our honored colleague, Dr. S. Weir
Mitchell, and his successful treatment of neurotic, bedridden women, is
increased by the use of a properly-modified current, galvanic or faradic,
as the case may be. Thus, the absorbing action of the hot baths of Hot
Springs or of Wiesbaden is heightened by galvanic massage, and the
sedative and stimulating action of tonic waters or treatment by faradic
massage.
The galvanic current alone causes a more permanent hyperaemia
without the disadvantage of the mechanical irritation of massage, and,
on the other hand, it lacks the advantages of the mechanical effect,—the
removal of stagnating blood and lymph; both together, properly applied,
re-inforce each other, the galvanic current making the effects of massage
more lasting. The rules for application are the same as for simple
massage. The method of action is well stated by Mordhurst as follows :
(1) the hyperaemia caused by massage is heightened and prolonged by
the contemporaneous application of galvanism, and this heightened effect
is achieved without the injurious influence of too intense mechanical
irritation, as severe and long-continued massage would produce it; (2)
by massage with the massage electrode the absorbed particles of the
pathological product, taken up by the lymphatics, are mechanically
removed from the diseased site; (3) the long-persisting hyperaemia in
the skin aids greatly in the depleting of the morbidly-affected lymphatics
in the neighboring tissues.
Galvanic massage is especially adapted for the treatment of articular
rheumatism and the removal of indurations and inspissated deposits, but
it is also used for the relief of neurasthenia and neuralgic pains.
Faradic massage augments the stimulating effect of massage, and
by the penetrating powers of the current extends its range of action to
the deeper tissues, without adding to the superficial irritation ; the
calming, sedative effect of the mechanical manipulation is likewise
increased by the direct action of tension currents upon the nerve-fibres.
Faradic massage is useful in various forms of nerve-exhaustion, neural-
gias and headaches, in chlorosis, in paralysis, constipation, muscular
rheumatism, and in certain phases of chronic articular rheumatism.
Although generally applied by a current from the ordinary battery, by
means of the plate or roller massage electrode, Butler uses an appa-
ratus of his own construction, in which the generator is within the roller
itself.
(c) The Faradic Bath and Douche.—Both faradic and galvanic cur-
rents are used in hydro-therapeutic treatment, and are combined with
A-156
ENGELMANN.
bath or douche, as the electric bath and the electric douche, and are used
in very much the same class of cases as electric massage, though more
general in its effect. The manner in which the bath is given varies with
the construction of the tub, whether this is of a conducting material or
not. If the tub is of metal, generally copper, the patient must be pro-
tected from contact with its walls by a lath-work of wood : one rheophore
is connected with the tub itself, and the current is thus carried by the
water to that part of the body which is immersed, the other electrode
being applied to a part out of the water. More commonly a tub of non-
conducting material is used ; porcelain" is best, but wood, coated with
white, non-metallic enamel, can be used, and is cheaper. The current is
generally passed lengthwise through the body, the back or shoulders
resting upon the non-conducting protector of the one plate and the feet
against the other; some use a larger plate at the head end, but others
(Trautwein) merely coil the terminal of the battery-wire a few times in
this electrode and use a large plate at the foot end ; for some conditions
the current is directed more to certain parts by small plates placed
accordingly. Back and feet rest against the protecting, non-conducting-
rim of the electrode, about one and a half inches from the plate itself;
it should not be too far away, in order not to diffuse and weaken the
current, as water, unless very warm, opposes far more resistance to the
current than does the body. The resistance of water as pleasant for a
warm bath is but a trifle greater than that of the body with the epidermis
saturated, and at 30° R., or 38° C, a hot bath, the resistance of water
and body is the same; so that the current-measure is the same, whether
passing in the bath through the water alone, or through water and body
in the tub.
It is said that about one-sixth of the current passes through the
patient (Steavenson), the saturation of the epidermis diminishing the
resistance greatly, so that from a galvanic current of 200 milliamperes the
patient receives 40 milliamperes. This diminution of resistance, which is,
of course, readily shown by actual measurement, is further marked by
the equality of closing and opening induction current in the faradic
bath, and by the inefficiency of tension currents from fine secondary
coils, which have almost no effect; hence the primary coil is used for
bath currents, or, better still, secondary coils of very heavy wire.
The important features in determining the result are : temperature
of bath, kind and intensity of current, and time of application. Plain
water is used, to which solutions are often added, but the mineral waters
of health resorts are preferable. From ten to fifteen minutes is amply
long for a first bath ; this is increased in time with the staying powers
of the patient, but should rarely exceed thirty minutes. It is well to
begin with the body temperature of 98° F., gradually increasing or de-
creasing as the case may demand. The strength of the current used will
depend upon the necessities of the case, but, as the time of application
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-157
is prolonged, it should never be very strong; the faradic current must,
however, be distinctly felt, and the galvanometer must be consulted for the
galvanic bath, as with the diminution of surface or skin resistance, and
the large surface of application, low density of current, it may produce
but little sensation, yet a powerful constitutional effect.
The faradic bath is the perfection of general faradization and the
direct opposite of localized electrization, the confining of the effect to
the diseased part; as it is frequently used to intensify the action of cu-
rative mineral waters, it is found in its greatest perfection in watering
places; the faradic current, thus used, in combination with a bath of
proper temperature, is a most agreeable sedative in neurotic cases, and a
pleasant as well as efficient stimulant in general debility, as from anaemia
or neurasthenia, and it is most unfortunate that this useful agent should
be more or less relegated to quackery. In place of being conscientiously
applied by skilled hands, under proper conditions, we find it in public
establishments, handled by an ignorant attendant, and given to whom-
soever pays for it, or, worse still, it is a money-making agent for the
advertising quack. In many instances the effect is, of course, pleasant
and satisfactory ; but if the patient be sensitive, or the case one contra-
indicating the bath or the current, the innocent seeker after health may
be carried away unconscious, or may receive a shock from which it will
take him or her days to recover. This useful remedy should be devel-
oped, and restored to the realms of legitimate medicine.
The faradic douche is an equally valuable agent in its proper sphere,
as a general application, in neurasthenic cases, and locally used in uterine
and spinal diseases. The douche proper, hot or cold, is used as the rheo-
phore, or conductor, to carry the faradic current, by which its efficiency
is greatly augmented : A large plate electrode is applied as the indiffer-
ent pole to a near surface of the body, and douche or spray, of proper
temperature, is thrown from the fluid-carrying rheophore, at a distance
of six to twelve inches, upon the part to be reached. It is an admirable
application in spinal weakness, and as a sequence to the bath, or alone,
in neurasthenic cases, producing a pleasant tingling feeling and a healthy
reaction; so also the cold spinal douche is given in or after the hot bath,
and the tonic and astringent effects of the uterine douche can thus be
augmented by the faradic current.
III. APPARATUS FOR THE PRODUCTION OF FARADIC
CURRENTS FOR MEDICAL PURPOSES.
A. Essential Features of the Apparatus.
The elements necessary for the production of faradic currents are
(a) a flow of galvanic force; (b) the primary circuit or coil; (c) the
strengthening core ; (d) the automatic interrupter; (e) the secondary
A-158 engelmann.
circuit or coil; (f) an appliance to vary the current-strength without
change in the flow of galvanic force.
I. THE GALVANIC INDUCING FORCE.
Galvanic currents of small quantity and low tension are used in the
production of faradic electricity, averaging from 1^ to 5 volts and from
200 to 1500 milliamperes, those of highest amperage having the lowest
voltage and vice versa, the Leclanche cells with lower amperage having a
higher voltage. The current-producers vary with the instrument. Those
most commonly used are (a) the sulphate of the binoxide of mercury
cell, which is extremely convenient for the pocket-battery, as the dry
powder, being in small bulk, can be readily carried about in a bottle
within the battery itself. The carbon forms the receiver or cup within
which the salt is dissolved in a little water, the zinc being placed into it
after stirring; a single charge gives a flow of forge sufficient to supply
the instrument for the longest seance, (b) The small bichromate of
potash cell: either upon the principle of the Grenet cell, or, as it is fre-
quently used in the portable box-battery, carbon and zinc in one cup and
the fluid in a second, well sealed with a rubber cork, so that it can be
poured into the empty cell when it is to be utilized. For the stationary
or sledge instruments wre generally use (c) the Grenet cell, giving a cur-
rent of If volts and 1^ to 2^ amperes, which is convenient, as it is ready
for use as soon as the zinc is dropped into the fluid ; but objectionable
on account of the acids employed, the fluid being a solution of bichro-
mate of potash and sulphuric acid. Preferable is (d) a couple of two
Leclanche cells, in which the harmless muriate of ammonia filling needs
but the addition of a little water once or twice in a year, if evaporation
is prevented by a well-fitting cover. Sometimes three or four are used
(two suffice for many purposes for some instruments), giving a current
of about 2§ volts and 250 milliamperes.
The Gonda-Leclanche or the permanganate of potash cell—in fact,
any couple of one of the numerous similar elements, with harmless fluid
and cover to prevent evaporation—is most suitable, as the current is
established as soon as the circuit is completed, the apparatus being set
in motion by a turn of the switch.
II. THE PRIMARY CIRCUIT.
The primary circuit, always stationary, is, as we have seen, a sole-
noid consisting of a number of turns of well-insulated copper wire,
wound in regular layers upon a hollow cylinder of non-conducting
material, wood or hard rubber, with the zinc connection inside of the
coil. Wire of moderate thickness and length is used, frequently No. 22
wire, 0.7 millimetre in diameter, so that as little resistance as possible is
opposed by the conductor itself to the primary galvanic flow ; and yet it
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-159
must admit of sufficient electro-motive force to push the current through
the long secondary coil; though it cannot be too thick, so as not to
occupy too much space. This primary coil must be proportionate to the
battery-force employed ; the magnetism produced by the solenoid in the
core being proportionate, as long as the customary small magnetizing
force is employed, to the intensity of current and the number of wind-
ings of wire; but after a certain force is reached the increase in magne-
tism becomes less marked and tends more and more to a limiting value,
which is greater for soft than for hard iron or steel.
Too many windings or lines of force render the instrument bulky
and decrease its power. The large sledge instruments of Edelmann and
Waite & Bartlett have a primary coil of 22 wire (0.7 millimetre in diam-
eter) in from 4 to 6 layers, with from 200 to 400 turns ; smaller instru-
ments are made with coils of fewer turns and often thicker wire, giving
a sharper current. The large instrument of Gaiffe has a primary coil of
0.7 millimetre wire with 1150 turns, forming a spool 19.7 centimetres in
length by 3.8 centimetres in diameter,—shorter than that of Edelmann
and longer than that of Waite & Bartlett. This circuit is always closed
unless opened by the interrupter; but if the primary or direct extra-
current is to be utilized, it is switched off at the extremities of the coil
to two binding-posts, from which it is taken, thus forming a branch cir-
cuit which is generally open, and closed only by the object through which
the primary current is passed, when this is to be utilized.
III. THE CORE.
The strengthening magnetic core, by which the magnetic force of
the surrounding solenoid is increased, depends for its efficiency upon its
conductivity; that is, the rapidity with which it is magnetized and
demagnetized, the rapidity of variation or change of potential determin-
ing the physiological efficiency of the current produced.
A bar of soft iron was placed within the hollow of the primary
cylinder, projecting a little at either end, beyond the cavity of the
spool ; soft, well-heated iron was employed, as this material is magnetized
and demagnetized most readily ; yet disturbing induction processes, or
eddy currents, were found to take place within its mass, which led to a
loss of power, so that it was supplanted by bundles of well-heated soft-
iron rods carefully insulated. Spirals of wire are also used ; and the
core of the Engelmann instrument consists of a sheet of soft iron, as thin
as paper, rolled into a cylinder, which seems to magnetize and demag-
netize more readily, and also to give a more satisfactory physiological
effect than the wire core. This core may be fixed or movable, made so
as to be wholly or partially withdrawn, or it may be covered by a movable
copper or brass tube. This brass or copper cylinder, the tube of Du-
chenne, made to slide between core and primary coil in the pocket-battery,
and between primary and secondary coil if used in a sledge instrument,
A-160
ENGELMANN.
but, as a rule, found only in small instruments of simple construction, is
used to vary the strength of the current. The method is simple, yet
unsatisfactory, as the presence or withdrawal of the tube weakens or
strengthens the physiological effect of the induced current without
changing its quantity, and weakens it but imperfectly.
The presence of this tube acts as a damper on the magnetic forceps
of the core by interfering with the lines of force from the coil to the iron
core by counter-currents which they themselves produce in the cylinder,
and thus the opening or break current is modified in its intensity. With
the opening of the current in the primary coil two currents are induced,
one in the copper cylinder and one in the secondary coil; both have the
same direction and induce in the other conductor a current contrary to
the first; the result is that the induced current is hindered in its ascent,
the curve is flattened, its physiological effect is diminished, although its
galvanometric quantity remains unchanged.
IV. THE INTERRUPTER.
(a) Importance.—The current-breaker, interrupter, trembler, vibrator,
or hammer, as still made in the great majority of medical instruments, is
merely the automatic arrangement by which the changes of potential in
the galvanic flow, which develop the induction current, are produced in
rapid succession, without manual interference, by the successive making
and breaking or closing and opening of the primary current, and all that
is required of it is a uniformity of action, as indicated by a " clear note "
or a smoothly buzzing sound ; yet this mechanism—upon which the very
being of the faradic current is based—is one of the most important fac-
tors of a serviceable faradic apparatus, as, by a variation in its action, all
other conditions, such as battery-current and position of coil, remaining
the same, the character of the current is changed and its intensity or
physiological effect can be varied from a minimum to a maximum inten-
sity by variation in time and phase of the rise and fall of the potential,
and also by the rapidity with which rise and fall of like phase succeed
each other. In the primitive state in which it is found in most medical
instruments it is deprived of all significance but that of a simple inter-
rupter and maker of induction force, all that is demanded of it being that
it " do not make a rasping noise or act irregularly."
(b) Number of Interruptions.—The interrupter as generally made
vibrates between thirty and fifty times in the second,—that is, at the
highest, about 3000 per minute,—and thus serves to establish an induced
current of a certain quality ; but as its physiological effect is varied by
number and character of these interruptions, and a single trembler rarely
admits of sufficient variation, one or more interrupters are attached to
the more perfect instruments.
The most satisfactory arrangement we have had is that by which the
character of the interruptions can be varied and their number changed at
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-161
will: this is attained to a certain degree in the Waite & Bartlett instru-
ment with two interrupters, from 1 to 50 or 60 per second, and in the
Gaiffe instrument, with one trembler, only up to 50 per second,1 and by
the single impulse-key, with which each of these instruments is supplied,
they can be made at will, by manual pressure, in very slow succession.
Simple as this appliance is, and important as it is for purposes of diag-
nosis and muscular massage or stimulation, it is not found in the average
medical instrument.
I regret that space does not permit my entering more fully upon this
subject, as my recent experiments demonstrate most unquestionably that
the interrupter is one of the most valuable factors in current control and
variation, and that the range and utility of the faradic current will be
greatly enlarged when instruments with properly-variable tremblers or
interrupters are given to the profession ; and these must be such that
they can be set at will from one to many hundreds per second, must be
entirely independent of the galvanic flow which acts the coils, and pro-
pelled by a separate and distinct motive power.
(c) Kinds of Interrupters.—Contact-breakers as now made are of
three kinds, (1) the core itself serving as the attracting magnet, or (2) a
separate magnet is formed ; but in both the battery-current, which serves
as inducing force, also determines the magnetizing and demagnetizing
of the magnet, which causes the vibration; but (3) in instruments of
precision the contact-breaker is an appliance separate and distinct from
the induction apparatus, with a motive force independent of that of
the instrument proper. I may add (4) the single impulse-key and (5)
the rapid controllable interrupter, which must be added to a perfect
instrument.
The contact-breaker in small instruments and in those of more
simple construction consists of a spring with soft-iron hammer-head,
platinized, in which the wire of the primary circuit terminates; the
force of the spring presses the hammer-head against the other part of
the vibrator,—a platinum-pointed screw,—which forms the terminal of
the battery wire, thus establishing the flow of force, rendering the core
magnetic. The hammer, being placed within the magnetic field, within
one-sixth to one-fourth inch from the core, is attracted to this soft-
iron terminal, breaking the primary galvanic circuit, whereupon the
core is demagnetized, becomes neutral, and releases the spring, which
flies back to the battery terminal and the process is repeated. The
rapidity of vibration in the average instrument can be regulated, within
moderate limits, but not sufficient to determine any marked variation of
physiological effect; this is done by the platinum-pointed screw, which
controls the length of oscillation by increasing or decreasing the distance
1 Since writing the above the singing rheotome has been adapted to several instruments and
gives vibrations of much greater rapidity; unfortunately, it is not possible to regulate and con-
trol these as it is ,necessary to do for therapeutic purpose-*, and the vibrations vary with the
battery force employed, as the rheotome is not independent of this.
11
A-162 ENGELMANN.
between core, or magnet, and screw-point or battery wire, within which
the hammer moves.
In most larger instruments of foreign make the attracting force is not
the core, but a small electro-magnet entirely independent of it, formed by
the coiling of the battery wire around a soft-iron horseshoe ; and it is of
necessity so, in all instruments in which the battery force is varied by
withdrawal of the core, as this must be movable without interfering with
the efficiency of the apparatus. This is the ordinary contact-breaker,
the hammer of Neef, or Wagner-Neef, which is more or less complicated
according to the perfection of the instrument, yet never practically varies
the effect of the current. Screw-point and hammer-head are always platin-
ized, in order that oxidation may be prevented and perfect contact may be
interfered with as little as possible; the bright spark formed at these
points would rapidly destroy other metals, and even the almost invulner-
able platinum is gradually coated with a thin film and slowly corroded so
that the point of contact must be occasionally changed, and in time, after
long use, even the platinum must be replaced. The platinum surface
should be cleansed and the delicate film of oxide removed, as it offers a
resistance, an obstacle to the passage of the current, which causes loss
of power. ' ; ''-■-■
Independent Interrupter.—In faradic instruments of precision the
motive power for the contact-breaker is supplied by a separate current,
independent of that supplying the inducing force : this is a change which
I deem important, because I have found that the vibrations of the
trembler, in instruments as generally made, are varied by every change in
the inducing flow and in the position of the coil, and also on account of
the disturbance in the current caused by the self-inductive action of the
separate electro-magnet attracting the hammer. In my new instrument,
as made by Waite & Bartlett, the inducing current enters the primary
circuit directly and is made and broken by the action of the vibrator,
which is set in motion by an independent force. This I deem the only
method of interruption for a complete instrument, being entirely inde-
pendent of the coil current proper, as it is acted by its own battery force,
and it is a method which can be adapted to every kind of interrupter.
Very slow interruptions are produced by a pressure upon a spring,
the single impulse-key, such as is found in the Gaiffe and Waite &
Bartlett instruments.1
The better instruments are furnished with improved contact-breakers
of varying form, some of them having two or three,—rapid, slow, and
single impulse,—the slow vibrator varying from 1 to 20 in the second,
and the fast spring with from 20 to 60 oscillations per second ; the singing
rheotome of the Galvano-Faradic and Dry-Cell Battery Company's in-
strument is a horizontal steel vibrator, far more rapid than the above
1 Since writing this other instruments have appeared with the single impulse-key, which
is a valuable addition.
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-163
vibrators when currents of sufficient power are used. Although ad-
mitting of rapid vibrations, these vibrations, as already stated, are not
sufficiently controllable, and not controllable to a sufficient extent to
make this method one which is available for medical instruments of
range and precision ; moreover, as considerable battery force is necessary
to act this rheotome, the same strong currents which are necessary to
act the rheotome must be used for the coil, and mild currents, which are
frequently needed in therapeutic applications, are inadmissible.
To attain all the varying physiological effects more rapid contact-
breakers, not necessarily vibrators, such as I have suggested and Messrs.
Waite & Bartlett have constructed for me, are needed ; these are inde-
pendent of the primary galvanic flow and controllable, as I consider it
to be of great importance that the operator should know, approximately,
at least, the number of interruptions for purposes of scientific research
or therapeutic record. The interrupter is arranged so as to indicate,
within reasonable limits, the number of oscillations at any given point.
This interrupter is a separate instrument, which may serve as inter-
rupter or alternator for galvanic or faradic currents, primary or sec-
ondary ; the speed is obtained from the shaft of a motor propelled by a
Grenet cell or storage battery, giving 50,000 interruptions per minute,
as I believe that 50,000 per minute, 800 per second, is a rapidity suf-
ficient for therapeutic purposes, though I have experimented with inter-
ruptions of over 100,000. I have as yet made no therapeutic tests of
these highest rates, and have had no more instruments so constructed,
as the results of my physiological experiments are such as to lead me to
believe, with great assurance, that the most satisfactory therapeutic
effects and all necessary current variations are obtainable with inter-
ruptions up to 50,000 per minute, and that higher rates are useless
unless the make of the induction apparatus is greatly changed ; with
instruments as now made 50,000 per minute is an extreme ; any number
can, however, be obtained, if desired, and always with precision. The
speed indicator, the rheostat, and galvanometer admit of a perfect
control of these interruptions.
Observations upon the physiological effect of variable interruption
are almost wholly wanting, for the reason that only trifling variations
have been achieved by the instruments hitherto furnished, and no index
to their number is given, nor can a desired number be attained at will;
so that it was simply impossible to record the work done, even within
the narrow limits which were allotted. • The only method we have had of
determining the number of oscillations of the interrupter was by com-
paring its note, or its musical interval, with the note of a tuning-fork of
known vibration, and even this is referred to but rarely, and used more
rarely still; it is practically possible only to the perfectly-trained musical
ear. Each octave has twice the number of vibrations as its key-note, the
major third f, the fourth $, the fifth f the number. (Edelmann.)
A-164
ENGELMANN.
V. THE SECONDARY CIRCUIT.
The secondary circuit is that from which the alternating, inverse,
and direct current, the induced current proper, as generally used in
medicine, is taken ; hence it is an important feature of the apparatus.
Its force, like that of the primary circuit, is increased by increasing the
number of windings, each winding or turn of wire having the same
electro-motor force ; so that ten windings possess ten times the electro-
motor force of one, and in the completed coil we have the added effect
of each single winding or line of force. The quantity of electricity
passing is, however, inversely as the resistance offered by these windings,
the greater the less the resistance ; that is, the thicker the conducting
wire and the shorter it is, or the fewer the windings, the less resistance
do they offer. To be most efficient as an induction-current producer,
resistance and number of windings must be in proportion to the induc-
ing force, to the galvanic flow, and the magnetic power of primary
solenoid and core.
This circuit, like the primary, is constructed of well-insulated copper
wire, coiled in regular layers upon a non-conducting hollow reel, conaxial
with that of the primary coil, which fits into this hollow. As the strength
of the induced current depends upon the nearness of the inducing to the
secondary induction circuit, the layers of the secondary winding must be
as near as it is possible, without contact, to those of the primary, which
must fit closely into the very thin spool of the surrounding secondary
coil, and a limit is placed to the number of layers of its windings,—that
is, the thickness of the spool; its length, determining to some extent the
approximation of the circuits, likewise influences the nature of the re-
sultant induction current; but, although long spools have their advan-
tage, they likewise have their disadvantage, and the more smooth and
pleasant, yet therapeutically effective, currents are developed from the
secondary circuits coiled on shorter spools. This interesting and
practically valuable fact I cannot explain, but its truth has been proven
by repeated and careful tests of the best instruments, with every possible
length of coil. Within certain limits, dependent upon the inducing
force, the secondary coil should be constructed, in regard to resistance
and number of winds, with a view to the physiological or therapeutic
result to be obtained,—a feature which, to the great detriment of faradic
electricity, is hardly found in any of our medical instruments.
I am not as yet prepared to define positively the most efficient forms
of secondary coil for our various therapeutic needs, and will merely say
that I am now testing coils constructed in reference to the instrument
with which they are to be used, varying in resistance from 0.8 ohm
up to as high as 2500 ohms, and in number of windings from 528 to
12 000, with wire from No. 15 to No. 36 and 40,—the finest which can
be well insulated.
FARADIC CURRENT, MAGNETISM. MASSAGE, ETC. A-165
VI. METHODS OF VARYING STRENGTH OR INTENSITY OF
PHYSIOLOGICAL EFFECT.
Every apparatus for the production of faradic electricity must be
provided with some means of varying the current-strength without alter-
ing the primary galvanic force. The direct, primary or extra, current
is weakened by the withdrawal of the intensifying core, or by a decrease
of magnetizing power by the presence of the shielding tube; so that
these parts are arranged to be withdrawn or inserted at will; yet many
instruments are void of any such mechanism, as they ignore the
utilization of the primary current.
The essential feature is the gradation of the induced current, and
this variation of the electro-motor force in the secondary coil is attained
without change in the primary flow by varying the coefficient of mutual
induction of the circuits, by a change in their relative position, the ap-
proach or withdrawal of core, tube, or secondary coil; the latter being by
far the superior method. The object to be attained is the gradual varia-
tion of intensity, without jarring or irregularity, from a minimum to the
maximum of electro-motor force.
The removal of the core or its complete covering by the tube, whilst
rendering the current very weak, does not reduce it to a minimum, and
would necessitate the addition of a rheostat for thorough control; in
instruments in which the core serves as a magnet for the interrupter it
cannot be moved, and the tube is a superfluous addition and a detriment,
as it increases the distance between core and primary, or primary and
secondary circuit, weakening the induction effect. Moreover, the gal-
vanometric or measurable intensity of the current is not altered by re-
moval of the tube, however much the physiological effect is varied.
The quantity of flow remains the same, its curve only being changed;
hence the tube is used only in pocket-instruments, which must be very
compact, cramped into the smallest possible space, which does not admit
of a moving to and fro of the large secondary coil.
The only simple and practical method of varying the current is
by approach and removal of the outer or secondary coil from the
inductors,—primary coil and core,—which are fixed, and thus the in-
duction force can be varied from 0 to its maximum, and the change
established with regularity and precision. In the great majority of in-
struments, and in every more exact apparatus, the gradation of induction
force is produced by the sliding of the secondary coil over the primary,
and only to those so constructed do I refer in speaking of faradic in-
struments, as the galvanometric, like the physiological effect, decreases
with the removal of the secondory coil; and not alone is the effect
varied, but it can be graded, by the extent of separation of the coils, as
the electro-motor force induced in the secondary circuit is nearly propor-
tionate to the distance between the centres of the coils. The increase is
A-166
ENGELMANN.
very slow until the coils begin to overlap, then the current increases
rapidly with the pushing in of the coil; at four centimetres from com-
plete contact the ascent grows less brusque. The increase of electro-
motor force is less marked with still farther pushing in of the coil; when
near the end, at one centimetre, the effect is suddenly much reduced and
the increase is still less until contact is made.
Not alone is this the most satisfactory method of gradation, allow-
ing a gradual and regular increase of current and admitting of its utili-
zation throughout the entire range of its electro-motor force, but it
admits of a certain definition of current-strength, of record and com-
parison, by a subdivision of the sledge or slide, at will, in inches or centi-
metres, so that the position of the secondary coil can be noted as an
index of electric force.
The physiological efficiency of the current can also be graded from
0 to the maximum of physiological force by the contact-breaker in
properly-constructed instruments, by varying the rapidity of inter-
ruption ; but this, like the tube of Duchenne, in nowise affects the
measurable intensity ; although a regulator of therapeutic value, it is
useless for purposes of dosage, since the same status of the interrupter
has a different significance for different current-intensities as it has for
nerve and muscle.
B. Batteries Used.
I will not here refer to the rotary or magneto-faradic instrument, as
it is antiquated and rarely used, although perhaps preferable under cer-
tain circumstances, for its effect upon diseased muscle and for its con-
venience upon the frontier or in distant posts, as an instrument much
less liable to disturbance, and not dependent for action upon solutions
which may evaporate or deteriorate or are entirely out of reach ; so also
in emergeucy cases it is serviceable, as always ready for action.
Diseased muscle reacts more readily to the magneto-faradic than it
does to the galvano-faradic current, as the rise and fall of potential in the
former is less rapid, and time is an important element for the muscle cur-
rent. Therapeutic tests have proven this, and Gaiffe describes a case of
lead poisoning in which the muscle did not react to the galvano-faradic
current, but was forced to response by the magneto-faradic.
Healthy nerve and muscle react to from 0.28 to 0.56 micro-coulomb
of a condenser discharge (Edelmann), and time is a factor in the effect
of the discharge on diseased muscle, healthy muscle reacting to a con-
denser discharge of T^k^ second, whilst diseased muscle needs from
tooo to tutju second, and the greater length of time of the magneto-
faradic discharge induces its more potent effect on diseased muscle. The
oalvano-faradic are the medical instruments of the present day, and
these as universally used up to this time, are constructed on one and the
same plan, varying only in shape and size and in the mechanism and
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-167
perfection of their component parts. For the proper utilization of the
variable and valuable therapeutic properties of the faradic current an
apparatus more perfect in its interrupter and coils is necessary, but I
shall here confine myself to the instruments now in general use, as
these are the ones with which the physician must deal, for the present
at least, until the new apparatus is more generally understood and
introduced.
The faradic battery, or medical induction apparatus, is an electro-
motor in which we utilize the effect exercised by change of force in elec-
trized or magnetized bodies upon neighboring circuits, and in which the
closing current preponderates over the opening current, upon which
physiological power is concentrated so as to give this the utmost effi-
ciency ; this opening current, or current of break, is the essential feature
of the direct or extra, and likewise of the induced secondary faradic
current, as well as the gauge of strength and direction of both.
I need not describe all trifling differences of construction, prominent
among which is the Kidder single or continuous-coil apparatus, consist-
ing of a series of three or four conaxial coils, movable over each other, in
which the terminals of the secondary coils are not'free as in the ordinary
instrument, but connected with the primary circuit from which the cur-
rent is taken, so that the primary as well as the induction flow is utilized.
Since the individuality of the primary coil, an idea advanced by Duchenne
and long retained, is proven a myth, and the peculiar effect ascribed to it
has been showm to be due mainly to the quality of the coil,—the short,
coarse wrire,—we no longer use the primary current. We can obtain the
same effect from a similar secondary coil, the alternation of the secondary
current and the induction effect in no way interfering; so that we now
ignore the primary circuit, which does not truly give a pure interrupted
galvanic current, as the induction effect preponderates, but we arrange
the apparatus so as to concentrate its efficiency upon the secondary cir-
cuit, thus obtaining uniformity and a much wider range of variation,
greater precision, and the possibility of comparison.
Such is even the modern instrument, with variation in shape and size
in accordance with the purpose for which it is constructed, and greater or
less delicacy and perfection of mechanism according to price ; but at best
it is incomplete, and ere long I hope to be able to present to the profes-
sion an instrument which will enable us to properly utilize the valuable
qualities of faradic electricity.1
In the instruments as now in general use we have three distinct
styles : (a) the pocket-battery; (b) the portable or box battery ; (c) the
stationary or sledge instrument. In all the vibrator is acted by the coil
current or primary battery flow, whilst in my new apparatus the inter-
1 I may add that this instrument has just been completed, and has been displayed by the
maker at the World's Fair, receiving the highest award; and I can safely say that we may soon
hope to see it in the hands of the profession.
A-168
ENGELMANN.
rupter is propelled by a separate motive power, so as to interfere in
no way with the current proper.
(a) The type of the pocket-battery is the small Gaiffe instrument
(Fig. 8), a neat box no larger than an octavo book, with two small
sulphate-of-mercury cells, L, and with fixed coils, M, the core serving as
attractor for the spring interrupter, P, the current-force being varied by
the sliding tube, R. Extra and induced current, or both united, can be
utilized from the connections in E by brass sponge-holders, N, or the
metal electrodes, T. The battery-salt is carried in the bottle, K. Sim-
ilar small instruments are made in the United States.
(b) The instrument most generally used is the box-battery. This is
of moderate size and so arranged that it is portable, and yet can be made
so complete that it answers all purposes and is in general use as an office
instrument. These box-batteries vary greatly in size and perfection of
construction, and are all equally serviceable for purposes of irritation or
stimulation ; yet the great majority of instruments do not admit of any
other variation of current than in strength, as they have only the spring
Fig. 8.—Pocket-Battery.
interrupter, which cannot be adjusted sufficiently to admit of a physio-
logical variation of current, and they mostly have but one secondary
coil, and that of no great length of wire, thus giving a sharp current.
One of the most perfect of these instruments is the box-battery (Fig. 9)
constructed in accordance with my earlier suggestions, and possessing
controllable contact-breakers, which are well adapted for current-inter-
ruptions within moderate limits, and of greater variability than in other
instruments. We see the three coils, one in use and two others stowed
away in the receiver, and three contact-breakers; the rapidly-vibrating
spring, adjustable by the screw-head, D; the slow interrupter, whose
beats are varied by the screw, C, and the single impulse-key, H. The
galvanic flow is established by inserting the zinc, F, into the adjoinino-
bichromate-of-potash element, and making the battery connection by
means of the metallic bridges, E E. The coils with which this battery
is armed are those first advocated by me in 1886 : Coil I, 577 winds, 0.8
ohm resistance; Coil II, 1750 winds, 13 ohms resistance; Coil III, 4000
winds, 250 ohms resistance. They accompany every instrument and
suffice for ordinary needs, but for special or more delicate work others
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-169
must be added, as they are used with the new apparatus, and can be
fitted to this. Innumerable very excellent box-batteries are made, but
all on very much the same plan, with no possibility of current variation
save by the sledge; though we must make an honorable exception of the
Gaiffe and Flemming and the instruments of the Galvano-Faradic and
Dry-Cell Battery Company, the latter of which have but quite recently
appeared; in fact, our American instruments now far surpass those
made in other countries.
Fig. 9.—Box or Portable Battery.
(c) The Sledge Battery.—The most perfect instruments, such as are
furnished for cabinets and used by specialists, though on the same
principle, are not boxed up, and are always made in the form
of the Tripier or du Bois-Reymond sledge, a long slide or sledge
admitting of an extended withdrawal of the secondary coil, thus yield-
ino- maximum effects and minimum currents for delicate physiological
work. The utmost perfection of mechanism is found in this form of the
faradic apparatus, for which the galvanic force is supplied by a Grenet
A-170 ENGELMANN.
cell, or a battery of from 2 to 4 Leclanche elements. In most American
instruments of this form the core is the magnet which serves the
vibrator, whilst in those of foreign make the trembler is attracted by a
small electro-magnet distinct from the core; though I know of but one,
save my new apparatus, the Edelmann faradimeter, in which it is pro-
pelled by an independent force; yet such must be the case if any
precision is to be obtained.
Fig. 10 is one of the best instruments of this kind, showing an inge-
nious contact-breaker, /, attracted by the small electro-magnet, E, which
varies the interruptions from 1 to 50 per second by the change in the
slant of the bar, I, in moving the foundation, L, from L' to L", and by
varying the position of the globular weight, S ; P is the single impulse-
key, and i the current-reverser.
Fig. 10.—Slidue Instrument.
Fig. 11, varying only in detail from the box-battery, is the most com-
plete of the old-style instruments made to supply a medical current
as developed by the vibrator without the aid of the independent con-
trollable contact-breaker. The cut represents the old instrument with
the vibrator as propelled by the inducing current and attracted by the
core, whilst the new apparatus, with the same vibrators and coils, is so
arranged that the battery flow for each is independent of the other,
and both vibrator and coil current is supplied with a rheostat so that
every possible modification of force can be obtained, and the rapidity of
vibration need in no way be influenced by the variations in the inducing
flow, as is the case in all other instruments in which a change in
the position of the coils or the force of the inducing flow at once alters
the rate of vibration. This apparatus shows the same arrangements
for contact-breaking as Fig. 9, but is supplied with some additional
details, such as a fine movement, J, for the gradual sliding and pre-
FARADIC CURRENT. MAGNETISM, MASSAGE, ETC. A-171
cise adjustment of the coil on the sledge or scale. The long coil of
fine wire is supplied with a lever, K, by means of which different
lengths of wire can be utilized; thus, in one coil of 6000 feet the wire
is so switched off that it may serve as a coil of 3000, of 4500, or of 6000
feet. Any number of the four elements supplying the primary force
can be employed, by
means of the lever A,
from 1 to 4, as may be
demanded by the nature
of the circuits employed,
the resistance of the bat-
tery and body circuits, or
the effect to be obtained.
An instrument vary-
ing in several important
elements from any pre-
viously constructed is my
new apparatus (Fig. 12),
which furnishes all the
different qualities of
faradic current with the
greatest possible range
of variation and under
the most perfect control;
so that I may say that it
is an instrument which
will establish faradism on
a firm basis as a thera-
peutic agent, since it ad-
mits of a perfect control
of the current and of a
precising so necessary to
dosage; but it will also
greatl}r extend the range
of its applicability, since
increased range of coils
and rates of vibration
give currents of thera-
peutic power hitherto
unknown.
This instrument differs from all others, in the main, in the following
points : (1) the separation of the vibrator or interrupter current from
the therapeutic or inducing flow ; (2) in the variability, controllability,
and rapidity of the interrupter; (3) in the range and precise definition
of the secondary coils; (4) in the possibility of interrupting or alter-
A-172 ENGELMANN.
nating primary or secondary current at will. The cut represents the
apparatus but partially.
The inducing current here used is entirely independent of the current
which produces the interruptions, be it by means of the new contact-
breaker here represented or by the series of vibrators which is also
attached to the apparatus as made for me; this inducing current can be
varied (a) by the use of any number of elements as introduced by
moving the switch to points 1, 2, 3, or 4; (b) by the sliding of the
coil on the graded sledge ; (c) by the rheostat directly in front of the
coil. The second rheostat, by the side of the first, is for the purpose of
regulating the vibrator current, for single-impulse key, slow and fast
vibrator, as in Fig. 11, but not represented here.
1. Coils.—To the right is the coil, with sliding scale and fine move-
ment. The coils used in connection with the apparatus are devised for
Fig. 12.'—New Engelmann Battery with Variable and Controllable
Interrupter and Alternator.
certain therapeutic purposes ; their quality and quantity is designated
by electro-motor force (number of winds) and resistance in ohms.
For motor, to the exclusion of sensory effect,—that is, the painless
influencing of the muscle,—secondary coils of the lowest possible
resistance are used, i.e., coils with a comparatively great electro-motor
force:—
» At the very last moment, while reviewing the proof of this paper, I was fortunate enough
to receive this cut (Fig. 12) of my new faradic apparatus, to the perfecting of which my leisure
moments during the past year have been devoted, and it is by reason of the tardy completion of
this new apparatus, new in principle and in construction, that I can here give but a brief de-
scription of its salient features. I must add that the admirable carrying out of my ideas and
the perfection of mechanical details are entirely due to Mr. Harry F. Waite, of the firm of Waite
& Bartlett, New York.
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-173
Coil 1: 528 winds, 0.8 ohm resistance.
Coil II: 6500 winds, 4.1 ohms resistance, No. 32 wire in multiple.
The opposite condition—revulsion, nerve irritation, without affect-
ing the muscle—is produced by a coil of high resistance and low electro-
motor force :—
Coil III: 528 winds, 180 ohms resistance.
The utmost penetration, together with general therapeutic effects, is
obtained by coils of greater electro-motor force and higher resistance :—
Coil V : tapped at three points, 4000, 6000, and 8000 winds, from 250 to 750 ohms re-
sistance.
Coil VI, producing the utmost sedative and even anaesthetic effect, is a coil tapped
at 5600, 9600, and 13,000 winds, with a resistance of 2500 ohms to its highest electro-motor
force.
Coil IV (II of the old set) gives rather a sharp, yet penetrating current, 1750 winds,
13 ohms resistance.
To better illustrate these figures I will say that the most efficient of
the coils in general use have been those of 3500 to' 4000 winds, or 2000
feet. Each of the coils I have in this apparatus answers a definite pur-
pose, attaining the desired result best without complication by other
unnecessary and often deleterious effects.
2. Contact-breaker.—To the left is the contact-breaker or alternator
and interrupter, a small motor propelled by an accumulator or by a
Grenet cell, on its shaft sin interrupter to one side and an alternator to
the other. This contact-breaker serves to interrupt the current from
2500 to 50,000 times a minute : slower interruptions are produced by the
large wheel in the centre of the figure, which also serves to determine the
rapidity of interruption.
The advantages of this interrupter are (1) that it is propelled by an
independent force, and may be used as interrupter or alternator for
secondary or primary current or for the galvanic ; (2) that the rate of
interruption is perfectly controllable and regular, in no way influenced
by the intensity of the therapeutic or inducing current.
The perfect controllability of this instrument, by speed indicator,
rheostat, and am-meter, enables us to record and dose the faradic cur-
rent, and its rapidity enables us to secure sedative and anaesthetic effects
which can be obtained in no other way.
The absolute precision of record is perhaps the most important fea-
ture, as this is something which has been repeatedly attempted but never
hitherto obtained, any comparison with the tuning-fork being at best but
vague and only possible now and then for an experiment, but of no prac-
tical value for the office or for clinical work, and, moreover, a regulation
of vibrators within the wider range necessary for therapeutic purposes
is impossible, at least for actual work. Higher rates of interrup-
tion can easily be obtained, but my experiments have shown that this
is practically useless for induction apparatus as now constructed; and
A-174
ENGELMANN.
until electro-motor force and resistance of primary and secondary coils,
as well as the quantity of the primary flow, is greatly changed, we cannot
utilize interrupters more rapid than this, giving 50,000 interruptions per
minute.
C. Electrodes.
Electrodes, or instruments for the therapeutic application of the
induced current, are many and varied in shape and material, according
Fig. 13.—Sponge-Covered Disc
to the part to which they are to be applied and the purpose for which
they are to be used ; yet the paucity and simplicity of the electrodes
which accompany the average faradic apparatus, the old-time brass or
vulcanite sponge-cup, or the now universal sponge-covered disc, has done
much to limit the use of faradism, these being given into the hands of
the physician as the instruments for its application, yet serviceable only
for a very limited range of therapeutic use.
Strange as it may seem, the electrodes, or instruments devised for
the therapeutic application of faradic electricity, are more numerous and
V
\.
y
Fig. 14.—Plate Electrode.
diversified than those for the galvanic current, as its uses are more varied
and it is more liable to be applied to deep-seated organs and to the cavi-
ties necessitating instruments of peculiar construction for each separate
part; numerous electrodes are made for localized and bipolar faradiza-
tion, for faradic massage and the faradic bath, and I will briefly describe
the more important, as they are by no means so well known as galvanic
electrodes.
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-175
I. ELECTRODES FOR GENERAL AND LOCALIZED FARADIZATION.
In polar treatment we use the dry metallic electrode for superficial,
revulsive, or skin effects, and the moist electrode for muscles, nerves,
and deep-seated tissues, for the penetrating current. Metallic electrodes
are the circular or rectangular discs and plates of the instruments in
Figs. 13 and 14, small globes and cones, and the faradic brush,—a bunch
of fine wires trimmed so as to present a smooth, even surface. Instru-
ments of suitable shape are made for the application of this current to
the vocal cords, the uterus (Figs. 15 and 16), and the bladder.
In scientific experiments it must be remembered that the polariza-
tion of these electrodes affects the current more or less, and that for pur-
poses of precision non-polarizable electrodes must be used, or at least
Fig. 15.—Cup-Shaped Electrode for Os Uteri.
the extent of this'action must be studied and accounted for. Every
particle of oxide on the surface of the electrode offers a resistance to the
current, and thus weakens its effect; so that much current-strength is
lost in old, badly-kept instruments. More generally used are the moist
electrodes, made by covering the conductor with an adaptable moisture-
retaining substance, for penetrating, nerve and muscle currents.
The sponge was, until of late, universally employed,—an uncleanly
appliance, as it was used again and again, for patient after patient; not
alone dirty, it was imperfect, as its coarse meshes did not admit of close
adaptation to the part to which it was to be applied; and as resistance
and density of current are in direct relation to the surface of the elec-
trode, this is an important factor ; unless perfect coaptation and contact
at every point exist, the size of the electrode is by no means equivalent
Fig. 16.—Beard and Rockwell's Intra-uterine Electrode.
to its active surface, that surface being constituted by the points in close
contact with the tissues. Moreover, the penetrating power of the electric
fluid is dependent upon the resistance offered ; and as, for induction cur-
rents especially, the surface or skin resistance is great, the perfect coap-
tation of the electrode is of importance, as it serves to overcome this,
lessens the pain, and adds to the efficiency of the current by causing a
diminution of the resistance of contact or passage (Uebergangs Wieder-
stande). Cloth and the ordinary chamois, even when wet, has a rough
surface and does not admit of perfect contact as an electrode covering ;
nor does it hold enough moisture, upon the superabundance of which we
must rely for perfect contact, as no material can adapt itself to every little
A-176
ENGELMANN.
irregularity of the skin as water does. The saturating fluid serves to
make more points of contact, and, by moistening the dry epidermis, to
reduce its resistance,—an effect which is increased by increasing the
conducting powers of the fluid by warmth and the addition of a small
percentage of salt.
We need, for penetrating, painless currents, electrodes with the
greatest possible number of points of contact for their surface, as the
Fig. 17.—Ball Electrode.
density in each is diminished by an increase in their number ; hence the
metallic conductor of the electrode must be covered by a pliable and
adaptable material which will absorb and hold an abundance of fluid.
The cleanest and most simple is absorbent cotton, which is renewed for
each application : this can be used on all smaller electrodes, being
renewed for each application. Punk, which I use to cover larger plates,
is of finer texture and an equally good absorbent, and can be used to
advantage on the smaller instruments, a supply being kept on hand
Fig. 18.—Engelmann's Punk Electrode.
for renewal. Metal or carbon plate, ball or cone (Figs. 13, 14, and 17)
are surrounded by a thick layer of the cotton, which clings when moistened
and needs no fastening to hold it in place ; a rubber band will serve to
hold the punk. For the larger plate electrodes (Fig. 14) this can also be
used, and if it is to be permanent it may be held in place by a fine, thin
chamois ; one or two layers of well-selected punk, in place of the cotton,
underneath the chamois, are most satisfactory and make an admirable
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-177
conductor. The basis is a thin sheet of pliable tin, lead, or amalgam,
perforated in a number of places to give free access to the fluid.
This is the same electrode (Fig. 18) as the one I recommend for the
indifferent pole in galvanization, and made in the same sizes,the smaller
Fig. 19.—King's Rectal Electrode.
numbers being more generally serviceable for faradization; being flat and
pliable, it is extremely convenient for abdominal application, as it can
be slipped under the dress without disturbing the patient, a warm towel
Fig. 20.—Boudet's Rectal Electrode.
or a piece of rubber tissue serving to protect the garment from contact
with the moist plate. For labile applications the Erb electrode (Fig. 14)
with handle must be used, but covered in the same manner, the smaller
Fig. 21.—Tripier's Rectal Electrode.
sizes always with absorbent cotton or punk, and these, especially when
long and narrow, one-half by two inches, two by four, two and one-halt
by five though not so generally made, are very useful in local faradization.
Character and size of the electrode are prominent factors in deter-
A-178
ENGELMANN.
mining therapeutic effect, as upon this depend density and resistance,
the character and effect of the current, and these points must always
be noted for purposes of record and comparison, In body-cavities a
quantity of fluid to which the current is carried by the electrode may
serve as distributor; thus, in the rectal electrode of King (Fig. 19) or
that of Boudet (Fig. 20) warm salt water is irsed as the active pole within
the bowel in the treatment of constipation. This is a great improvement
over the old-time instrument with metallic end, which so long stood in
the way of this valuable method of treatment, which, if ever attempted,
was soon discontinued on account of the sharp, painful current from the
metallic electrode, which, moreover, was far less penetrating, less diffuse
Fig. 22.—Vesical Electrode of Boudet, with Manometer.
and effective as a muscular stimulant and contractor. In this instrument,
as in that of Boudet or the new electrode of Waite & Bartlett, no
metal can possibly come in contact with the tissues; in the former the
vulcanite bulb, in the latter the rubber catheter, through which the fluid
is injected, guards the tissues against the inclosed metallic conductor.
A similar instrument is the vesical electrode of Boudet (Fig. 22), to
which a manometer is attached for the purpose of recording the various
phases of the disease, by measuring the contraction of the vesical muscle
produced by the current in the course of the treatment.
(b) Bipolar electrodes are those in which both currents are applied
by means of one and the same instrument, which carries the two poles,
and are mostly used upon the mucous membranes, within body-cavities, in
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-179
uterus, vagina, bladder, and rectum. Thus the rectal electrode of Tripier
(Fig. 23) and a similar instrument by Bergognie (Fig. 24), supplied with
a manometer for the study of the contractile powers of the sphincter
muscles. The rubber bulb, B, is compressed by the contraction of the
muscle as it responds to the electric current, and the extent of this re-
action is indicated by the manometer connected with the bulb by a rubber
Fig. 23.—Tripier's Rectal Electrode.
tube, C. The instrument is a valuable one for the determination of
the cause of constipation, the determination of the extent of muscular
weakness, and the observation of its improvement under this admirable,
but little-used, method of treatment. Whilst this instrument is admira-
bly adapted for purposes of observation and measurement, it is, like all
metallic electrodes within the bowel, unfit for continued treatment.
Fig. 24.—Bipolar Rectal Electrode of Dr. Bergognie, with Manometer.
Only the cotton-covered instrument, or, better still, the catheter appa-
ratus, with water as the conducting agent, should be used, and, further,
it is rarely the case that only one point is affected, demanding the local-
ized application by a bipolar electrode; the polar method, with one ab-
dominal electrode, is decidedly preferable. Bipolar intra-uterine applica-
A-180
ENGELMANN.
tions are far more frequent and numerous: instruments are made for this
purpose, but these are mostly useless or dangerous in all but large cavi-
ties, as they are not pliable, and of necessity not sufficiently slender, car-
Fig. 25.—Bipolar Intra-uterine Electrode of Apostoli.
vying two insulated conductors ; so that they cannot be inserted in a
narrow or curved canal unless some force is used. Fig. 25 is the bipolar
intra-uterine electrode of Apostoli, and Fig. 26 that of Gunning. Va-
Fig. 26.—Gunning's Flexible Double-Current Intra-uterine Electrode.
ginal electrodes of various kinds are made; that of Tripier consists of
the insulated blades of a speculum, but mostly the two poles are upon a
rubber bar, as metallic circlets (Fig. 27), one to two inches apart, or
Fig. 27.—Bipolar Vaginal Electrode of Apostoli.
longitudinal strips parallel to each other: the surface of the metal is
generally even with that of the non-conducting stem and does not come
thoroughly in contact with the tissues; this difficulty is obviated in the
Fig. 28.—Bipolar Vaginal Electrode.
admirable instrument (Fig. 28) recently furnished by Waite & Bartlett, in
which the metallic poles are rounded, protrude over the stem, and are so
arranged that they can be approximated to or removed from each other.
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-181
Quite a variety of electrodes are constructed for diagnostic pur-
poses, especially for the testing of cutaneous sensibility: these are
pointed, conical instruments, and carefully-made wire brushes ; but as
the points of the wires in these brushes cannot all be made perfectly
even, bundles of wires imbedded in a vulcanite mass are used; the ends,
cut square and polished, present a smooth, metallic surface, in which
each terminal is in the same contact, and it is sufficiently large (two
centimetres in diameter), with a sufficient number of points to overcome
any source of error from perspiration, irregularities of the skin, small
nerves or glands.
II. MASSAGE ELECTRODES.
For the application of faradic massage we use rollers or plates
made of a conducting material, and supplied with a handle, so that the
Fig. 29.—Piffard's Rolling Rheophore.
current is carried by the same instrument which exercises the pressure
upon the tissues. The electrode of Mordhurst is a plate, varying in
size according to the part of the body to be treated, with a medium of
one hundred and twenty square centimetres ; of the rollers, the rheo-
Fig. 30.—Wristlet Electrode.
phore of Piffard (Fig. 29) is a type ; another instrument is the wristlet
electrode (Fig. 30) for rubbing, massage, and digital diagnosis.
III. BATH ELECTRODES.
The electrodes in use in the faradic bath are generally large plates,
preserved from contact with the body by non-conducting, protruding
frames (sometimes an air-cushion is used), the metal plate being some
ten by twelve inches for the back or neck, and nine by eleven at the
337�2373
A-182
ENGELMANN.
foot end. Smaller electrodes are made for the purpose of localizing the
current in the bath to some one part of the body ; but for a general dis-
tribution of the bath-current the large plates generally used are entirely
unnecessary, as a few inches of the terminal of the battery-wire flattened
out or coiled answers precisely the same purpose, and must, of course,
be likewise preserved from contact with the body.
Local baths or douches are applied by means of metallic spouts, with
a non-conducting handle; these spouts, like those of a shower-bath or
watering-pot, are perforated ; the water is forced in delicate jets through
the numerous small openings, the spray being the rheophore by which
the current is applied to the part. For back and chest the spouts are
rectangular, or round, some two inches in diameter; a long, narrbw one
is made for the spine, three-fourths to one inch by two or two and one-
half inches; a plate-electrode is, of course, necessary for the indifferent
pole.
IV. CHOICE OF BATTERY AND ELECTRODES.
The proper selection of apparatus, of battery and electrodes, is all
important to the physician who would use faradism to advantage in his
practice, and afford his patient all the benefits of this variable and effect-
ive form of electricity. Notwithstanding the off-hand statement made
in so august a body as the International Congress of Electricians, only
one year ago, that "derkleine Spanner," the average small German box-
battery, was sufficient for all purposes, the choice of an instrument is of
great importance, and, although a recent text-book tells us that it is " of
small importance," as " the details of construction can safely be left to
the maker," and certainly far less important than the choice of a galvanic
apparatus, this is by no means the case. The choice of the faradic ap-
paratus is all-important, as upon its mechanism and construction depend
the character and efficiency of the current, whilst this is not the case in the
galvanic battery. The galvanic current is the same whether taken from a
home-made instrument of two dozen fruit-jars into which the carbons and
zincs are placed, if they are but properly coupled, or if it is from a battery
in mahogany box or cabinet; but the character of the faradic current varies
more or less with every detail of construction, with length, thickness, and
kind of core, dimensions of coils, length and thickness of wire, insulation,
number and character of interruptions; and its utility depends greatly
upon the method of contact-breaking and of gradation of current.
The physician who desires not only an irritating, stimulating cur-
rent, but wishes to obtain the utmost efficiency and variability of faradic
electricity, must consider various points. Granting precision and per-
fection of construction, as we may expect this in instruments from any
reliable maker, the essentials to be looked for are as follow :—
1. The possibility of varying the number of interruptions at will,
FARADIC CURRENT, MAGNETISM, MASSAGE, ETC. A-183
from one up to at least fifty thousand per minute (50 per second—3000
per minute—is the limit for the majority of instruments now used).
2. The separation of the inducing flow, or the coil current, from the
battery power which acts the trembler ; in other words, a separate motive
power must be used for coil and contact-breaker in instruments of pre-
cision from which an even and thoroughly controllable current is to be
expected.
3. The gradation of current-strength by the sliding of the secondary
coil over the primary upon a scale-sledge, which for a perfect instru-
ment should indicate in micro-coulombs the current-value for each coil,
for a given current, and for a given medium body-resistance, although
until a more perfect method of measurement is discovered the simple
division of the scale may answer. The mobility of the core is neces-
sary, and, of course, on a scaled slide; but this is not for the varying
of current-strength, but of current-quality.
4. The instrument must have a series of, at the very least, three
secondarv coils for muscle, nerve, and general effects ; one with low resist-
ance and as high an electro-motor force as possible, usually a short coil
of heavy wire ; another long, of not less than 5000 to 9000 winds, of very
fine wire, with one intermediary.
This is the very least that can be asked; more must be demanded
of an instrument from which the utmost efficiency and variability of
current is expected. The series of coils must have a greater range, and
each must be adapted to the special purposes for which it is constructed :
for muscular stimulation, for counter-irritation, for sedation, and for
general nerve and muscular effects. A fine-wire, multiple muscle-coil is
desirable, a short fine-wire coil for counter-irritation, and also a sedative'
coil with from 1000 to 13,000 winds. Above all, the contact-breaker must
be independent of the inducing current and be so arranged as to break
the contact any given number of times up to twenty or fifty thousand
per minute. As for the electrodes, I can only say that absorbent
cotton or punk should always take the place of the old-time sponge;
and perfect coaptation should be aimed at. whatever the nature of the
application, unless revulsive. For penetrating currents the material in
direct contact with the skin must be of fine texture, a perfect fluid-
absorber, and in sufficient quantity to retain it in abundance : the carbon
discs now in vogue are not as satisfactory as the metal, since they must
be covered in the same manner to secure penetrating currents; the
chamois or flannel covering with which they are sent out, as an accom-
paniment to the battery, makes an imperfect appliance, which but par-
tially answers the purpose for which it is intended, the resistance being
great and the adaptable surface comparatively small.
As electrodes must be selected with reference to the uses to which
the current is to be applied, and the range of application is so extensive,
the merits of individual instruments cannot here be discussed.
A-l 84 ENGELM ANN.
A great variety of efficient electrodes is to be had, each serving its
especial purpose, and the practitioner will soon discover the long-ignored
merits of the interrupted current if he will but study the nature of this
pliable form of electricity and avail himself of its variable powers by
using currents from properly-constructed apparatus, and apply them by
rheophores adapted to the object in view. Let the demand be created,
and numerous serviceable instruments will soon be placed within reach
of all.
GALVANISM.
By J. MOUNT BLEYER, M.D.,
NEW YORK.
In preparing this resume of research and investigation, so far-
reaching and comprehensive, I naturally cannot fail to accord due
credit to the tireless workers to whom our profession is indebted for its
knowledge of electrical energy as we now understand it. Particularly
let me thank those gentlemen whose works I have made use of, and to
whom credit is given in the " Bibliography."
In touching upon the critical value of batteries and precision instru-
ments employed by medical men, I shall leave what comment there is
to be made to my co-editors and colleagues who have prepared the other
chapters of this work, and upon whose ground I do not mean to tread.
While engaged in my labors I kept in mind that all-important considera-
tion, that most busy medical men will hail with delight and read with
interest what little I have to say upon the elementary physics of elec-
tricity. This, it seemed to me, was all important for a clear understand-
ing of the practical application and usefulness of electricity to the prac-
titioner. The mathematical consideration of the science I have only
superficially touched upon, but refer you to the many exhaustive
treatises on electrical measurements for additional light.
Historical Sketch of the Rise of Electricity.
To wield the thunder-bolt was the marked attribute of the chief
gods of old ; the lightning-flash was the surest proof of the presence of
the divinity. Indra, the Jupiter of the Hindoos, was the god of
thunder; the Etruscan Tinia always guided the electric storm ; Jupiter
Tonans waved his thunder-bolt over trembling Rome ; and in every
form of ancient superstition a belief in the divine origin of the most
startling of the heavenly appearances lay at the base of the national
faith. When it thundered the grave Romans dissolved their political
meetings and the wise Greeks listened with unfeigned awe. The gods
spoke from the heavens in the rattle of the passing storm, or wrote their
rage upon the earth in the ruin of the lightning-stroke. And now, like
Indra, Tinia, or Jupiter, the genius of modern civilization bears in its
right arm the thunder-bolt as its crowning attribute. It has snatched
the lightning from the skies and made it the most docile of servants.
The electric flash is busy day and night in doing the work marked out
for it by our modern magicians. It flies swifter than Ariel to carry its
master's message, and puts a girdle round the earth. It dives in mid-
ocean, rides over desert and forest. It prints our books, prepares our
(A-185)
A-186
BLEYER.
paper; it dissolves our gems and consumes platinum. An electric light
turns night into day ; electric processes aid almost every kind of me-
chanical labor; and the thunder-bolt of Jupiter is everywhere toiling in
the cause of human progress.
Of all the achievements of modern civilization this is the most
B'ig. 1.—Benjamin Franklin.
remarkable. Steam is gross and material; there is little that is poetic
or great in the rattle of the train or the roar of a monstrous engine.
We can easily account for the mightiest of machines impelled by boiling
water. Gunpowder and nitro-glycerin, oxygen and hydrogen seem the
natural servants of inventive man. But when we attempt to catch the
idea of the electric spark, it still appears almost as superhuman and ter-
GALVANISM.
A-187
rible as when it flashed fear into the hearts of Greeks and Romans. It
obeys with scrupulous accuracy ; it performs the smallest, as well as the
most important, tasks with equal care; it is as docile as was the genie
to Solomon's seal; and yet it still remains shadowy, mysterious, and
impalpable. It still lives in the skies, and seems to connect the material
and the spiritual. Whence come these tongues of fire; these sharp
shocks ; these pale, ghostly lights that play around us and mock the
master they obey ? Who is it that wields this electric element, which
seems to be the very base and source of our existence?
Some such sentiment of mysterious awe pressed upon the mind of
Thales, the Franklin of Miletus, when, twenty-five centuries ago, he
probably discovered electricity.1 A sage of Greece, the philosopher's
keen eye watched the minute phenomena of nature. His mind was
eager for every kind of knowledge. He studied morals, metaphysics,
life ; and upon a narrow field of facts he erected vast fabrics of specula-
tion, which were designed to embrace the whole origin and destiny of
man. Phoenician voyagers, who were in the habit, in that dim age, of
sailing out of the Straits of Hercules, and, perhaps, of coasting along
the desolate shores of Europe until they reached the Baltic, brought
back from the savage seas of Prussia a substance greatly prized by the
ancients for its fair color and delicate transparency. It was amber, or
electron.2 The natives found it floating upon the waves, or, perhaps,
gathered it from the mines which still form a source of the wealth of
Prussia, and the amber imported from the distant north was an impor-
tant article of commerce with the southern natives. But to Thales it
possessed a mysterious value. He discovered that electron, when
rubbed, had the property of attracting to itself various light articles, as
if endowed with volition. His discovery was the first step in the great
science of electricity. But the philosopher did no more than record his
observation and attempt to account for it, as he had already done with
the magnet, by ascribing to amber a soul. He supposed that some
hidden principle of life lay in the yellow jewel from the northern seas.
The discovery was never forgotten, and the peculiar property of
amber was noticed and commented upon by various ancient philosophers.
Theophrastus, three centuries later than Thales, observed the attractive
power of electron, and perhaps lectured his two thousand disciples upon
the animated gem. Pliny, the elder, also described the phenomenon,
and believed, apparently, that the amber was rubbed into life by the
action of his fingers. But the germ of the great science lay hidden in
mystery. No ancient philosopher could for a moment have supposed
that there was any connection between the animated electron and the
wild electricity of the thunder-storm ; that the same power was active
1 Becquerel, Traite de 1'Electricite ; Pliny, N. H., i. pp. 37, 329.
a Ges Carthager, Botticher, p. 75, thinks the Phoenicians reached Prussia. See Pliny,
H. N„ iv, p. 27; xxxvii, pp. 11,12.
A-L
BLEYFR.
GALVANISM.
A-189
in both, and that the secret of the amber was that of the thunder-bolt
of Jove ; that the precious electron was to create and to give a name to
the most wonderful of modern discoveries.
Yet electricity, in all its varied phenomena, never suffered the
puzzled ancients to rest.1 It flashed along the spears of their long array
of soldiers and tipped every helmet with a plume of flame. It filled
even the immovable Caesar with a strange alarm. It leaped down from
the clouds and splintered the temples and statues of Rome, and did not
spare the effigy of the Thunderer himself. It was seen playing around
the ramparts of fortified towns, crowning their sentinels with a strange
effulgence. Often the Roman or Greek sailors, far from land on the
stormy Mediterranean, saw pale, spectral lights dancing along the ropes
of their vessels or clinging in fitful outlines to the masts, and called them
Csesar and Pollux. But the science of electricity was still unborn. Mean-
time in ancient Etruria,the parent-land of Italian superstition, countless
students were being instructed in the art of reading the will of the gods by
the lightning.2 The heavens were divided into various compartments.
If the lightning-flash appeared in one, it was a favorable omen; if in
another, it was fatal. The accomplished augurs, instructed by long years
of study and toil, stood upon lofty towers, watching for the sudden
gleam or a sudden peal of thunder, and knew at once by their divine art
what undertakings would be successful, and when their warriors clad in
brass should go forth to battle against Rome. The religion of ancient
Etruria was almost a worship of electricity, and the land of Galvani and
Volta was famous in the dawn of its history for the close study of elec-
tricital phenomena.
But no Tuscan augur or Roman priest made any progress in creating
the science. Centuries passed away. Europe was torn by civil convul-
sions : men sank into barbarism and rose again into new activity ; but
the famous observation of Thales was never lost; and at length, in the
opening of the seventeenth century, an Englishman named Gilbert
began to study the properties of the electron. He was rewarded by
a series of discoveries that, in the dawn of science, made his name
famous over Europe.3 Yet they were so meagre as to advance little
beyond the early observations of Pliny. He enumerated various sub-
stances capable of producing electrical action ; he noticed the influence
of the weather on the electron and the magnet; and from his labors
sprang up a science known as electricity. Gilbert's work," De Magnete,"
was published in 1600, and soon the new science began to terrify and
astonish men. Every fact as it was unfolded seemed spiritual and
supernatural. Flames of fire played around the electrical substances in
the dark ; sparks glittered ; sharp sensations, produced by the unknown
1 Becquerel, i, p. 32. Plutarch, "Lysander," notices the luminous wonders.
3 Miiller, Etrusker, iii, pp. 1, 2. Arnob, vii, p. 26. Genetrix et inater superstitionis Etruria,
1 Becquerel, i, p. 35.
A-190
BLEYER.
agent, were felt by astonished operators; and a mysterious awe sur-
rounded the birth of the wonderful principle. Men were almost inclined,
like Thales, to invest the electrical substance with a soul.
An Englishman discovered electricity ; a Prussian, in the land of
amber, invented the first electrical machine. Otto Guericke, of Mag-
denburg, who also invented the air-pump, formed the instrument by
which electricity could be most readily produced ; he placed a globe of
sulphur on an axle, to be turned by the hand of the operator, while with
Fig. 3.—Electricity 150 Years ago.
the other he applied a cloth to the sulphur to produce the necessary
friction. It was a rude, imperfect machine, but it was at once found to
have made a great revelation in the science. Electricity, which had
heretofore been known only in its feebler forms, was now given out in
sharp sparks, and displayed a thousand curious properties. Sometimes
it attracted objects, at others repelled them. It seemed at times to exer-
cise a kind of volition. The weather affected it sensibly ; dampness dis-
solved its strength ; it was capable, too, of influencing* bodies at a con-
siderable distance, and was apparently independent of the usual laws of
GALVANISM.
A-191
space. Yet the seventeenth century glided away, with its fierce religious
wars and its wonderful voyages and settlements, while little progress was
made in the knowledge of electricity. Newton paid no particular atten-
tion to the new science. He suggested, however, that the electrical
substance was a subtle ether, filling nature, which could be set in motion
by friction. Yet his bold, inquisitive mind was never attracted by the
mysterious study; the flashes and sparks of the electrical machines
seemed, perhaps, a puerile entertainment to the great student of nature's
laws. Nor did any other eminent philosopher of the age suspect that
• Fig. 4.—Electricity 150 Years ago.
human hands would ever wield the thunder-bolt or unfold, by the aid of a
globe of sulphur, the mightiest principle of nature.
But in the next century electricity sprang at once into startling-
importance. A series of wonderful discoveries aroused the attention of
almost every scientific mind in Europe. England again led the way in
the path of investigation. Hawkesbee invented the glass electrical
machine,—a great improvement upon that of Guericke; and in 1730
Steven Grey began a course of experiments that unfolded the leading
principles of the science.
A-192 BLEYER.
France took up the study, and the curious discoveries of Dufaye
and Nollet excited the wonder of their contemporaries. Dufaye trans-
mitted the electric spark through a cord thirteen hundred feet long; and
at length, in conjunction with the Abbe Nollet, he performed an experi-
Fig. 5.—L'Abbe Nollet Watching the Expected Deadly Effect of a
Continual Electric Charge on Animals.
ment, with wonder and terror, that seemed the crowning mystery of the
science. Dufaye suspended himself by a silken cord, and was then
filled with electricity by the abbe. He presented his hand to his com-
panion, half doubting the truth of his own speculations, when a brilliant
spark shot from one philosopher to the other, and filled both with an
GALVANISM.
A-193
equal surprise. Never had such a wonder been seen since the days of
the Gothic warrior Walimer, who, according to Eustathius, flashed out
sparks from his body, or the ancient philosopher who could never take
off his clothes without emitting flames of fire.1
Not long after, however, an event occurred that seems to have filled
Europe with still greater wonder and awe. It was known as the Leyden
experiment. Professor Musschenbroek, who wrote an account of it to
Reaumer, can scarcely express in language the agitation and terror into
Fig. 6.—Battery of Leyden Jars, with Accessories.
which his unheard-of sufferings had thrown him. He had felt the first
shock of electricity prepared by human hands, and not the whole king-
dom of France, he declared, could induce him to take another. He had
been struck in the arms, shoulders, and breast, and two days elapsed
before he recovered from the mysterious blow. The professor, in fact,
had invented the Leyden jar. He had been endeavoring for some time
to inclose electricity in a safe receptacle, from which it could not escape,
except with his permission, and at length succeeded in imprisoning the
genie in a glass vessel partly filled with water. Suddenly he formed a
* Grey seems to have anticipated the experiment. Priestley's Hist. Elect., i, p. 66.
13
A-194 BLEYER.
connection between the two surfaces of the jar.1 The imprisoned elec-
tricity sprang through his body and shook him with a wild convulsion.
Novelty added its terrors to the unseen assault; his imagination was
filled with an indefinite alarm ; he shrank from his glass bottle as if it
were tenanted by the devil. Yet we soon after find him recovering his
spirits, and once more experimenting upon his powerful instrument.
The electric jar was soon employed in all the laboratories of Europe,
and everywhere terrified philosophers by the vigor of its shock. One
lost his breath, and believed that his right arm was forever disabled ;
Professor Winkler was thrown into convulsions, and had recourse to
cooling medicines to avoid fever; Abbe Nollet received a severe blow:
his body was bent, his respiration stopped, and he dropped the glass jar
in terror. Yet the shock of the Leyden vial soon became the favorite
amusement of court and saloon. It was exhibited before Louis XV at
Versailles, and a chain of two hundred persons, having joined hands,
received at once the mysterious blow. Each was severely shaken, and
it was curious to observe, says a contemporary account, how the peculiar
temperament of every individual displayed itself in the moment of
terror.2 Soon itinerant electricians wandered over Europe, astonishing
the unlearned and the rustics by administering electric shocks from the
Leyden jar; and the mysterious machines became familiar to the people
as well as to the court.
The jar was improved by coating its sides with a thin metallic cover-
ing; its power was increased; it was used in medicine to revive the
paralytic, or to open the lips of the dumb ; long sparks were drawn from
it that resembled flashes of lightning, and that killed unfortunate little
birds. A battery of jars was at length invented by Franklin which gave
shocks that reminded one of the terrible power of the thunder-bolt; and
the whole scientific world felt that it stood on the brink of some unpar-
alleled discovery.
The Franklin was already born, and his name had now grown great
in the science.3 His mind was of a peculiar cast that recalled the vigor-
ous simplicity of the Greeks. He was a modern Solon, a speculative
Thales. He had wandered away from Boston,—a printer's apprentice,—
and had found employment and success in Philadelphia. From his
parents he had received no inheritance, except the noblest,—a spotless
example, a healthful constitution, a sane mind; and, after a vigorous
struggle and several failures, the philosophic printer had won the respect
and the attention of his fellow-townsmen.
He founded schools, libraries, and various useful institutions in his
adopted home, and at 45 had become one of the most useful citizens.
Still Franklin lived obscure except to his narrow world, and his eminent
1 Priestley, i, p. 153.
a Academie den Science, 1746, p. 7.
* Sparks's Life of Franklin, vol. i, p. 152.
GALVANISM.
A-195
powers had won him no general renown. He had, perhaps, pleased him-
self in his youth with the hope of excelling in letters ; he had formed his
style by a careful study of Addison; he wrote clear and sensible essays
that showed the purity of his taste and the weakness of his fancy ; and
Fig. 7.—Engraving, reproduced from Nollet's Book, showing the Effects of
Electric Charges upon Evaporation, etc.
yet, in literature, he had been far excelled in notoriety, if not fame, by
his unprincipled companion, Ralph. Franklin's rare humor—the wit of
a philosopher—shines out in his " Busy-Body," his " Almanac," his
" Ephemera," or his famous " Whistle." He uttered keen apothegms
that lived like those of Solon, and sharp satires that want the bitter
A-196
BLEYER.
hopelessness of Diogenes. But his literature scarcely possessed the
shining marks of genius, and was plain, cold, and lifeless. He was an
excellent writer, but he was never great.
His genius, like Bacon's, lay in his power of swift induction from
moral or physical facts. In morals he was wisest of his contemporaries.
He taught young mechanics that "time is money," that "credit is
money," and that purity, honesty, and self-respect were better than
wealth, luxury, or any other success. His own labors were unceasing;
he wrote, toiled, thought incessantly for his fellow-men ; he was noted
and observed for his modesty and discretion; his acute mind was ever
seeking for useful novelty in science and in conduct; and hence, when
Franklin came to stand before mankind, covered with his splendid scien-
tific renown and the representative of the new republic that seemed
about to receive the classic refinement of a better age, he was received
in the courts of Europe as a worthy successor of the philosophers of
Athens and Ionia. As Washington appeared before the world clothed
in the purity, the probity, the valor of a Fabricius or a Cato, so Franklin
was universally compared with the acute sages and philosophers of
Greece.
To Franklin electricity owed the most wonderful of all its achieve-
ments in the eighteenth century.1 The obscure provincial observer was
led, by an accidental circumstance and his own eager fondness for
knowledge, to enter upon the study of the new science. Peter Collinsori,
a member of the Royal Society, sent over an electrical machine to
Philadelphia, and Franklin at once commenced a series of experiments
that led to remarkable results. Never, he wrote to Collinson in his first
letter, March 28, 1747, had he been so engrossed by any pursuit.2 All
his leisure moments were given to his machine. His fellow-townsmen
thronged his rooms to watch his novel researches. His labors were
rewarded by constant discoveries, and his wonderful inductive powers
soon led him to unfold, in his admirable style, the hidden principles of
the science. In 1747 he commenced writing to Collinson, in a series of
letters, an account of his researches in electricity. He gave clear direc-
tions for the performance of various beautiful or instructive experiments
that were wholly new and surprising. He explained the phenomenon
of the Leyden jar; he showed how iron points attracted electricity ; and,
at length, he declared that the lightning and the thunder were produced
by the same agent that was inclosed in the mysterious bottle, and he
urged the English philosophers to draw down the electricity of the skies
by placing iron points upon towers or poles, and thus test the accuracy
of his theories. His suggestions, it is related, were received by the
Royal Society with shouts of laughter. They refused to print Franklin's
1 Euler, Dis. de Causa Elect., 1755, p. 27. Idem assernit Franklinus, futuria experimenta
animo sagici quasi praemincians. (See p. 132.)
a Spaiks's Life of Franklin, vol. v, p. 185.
GALVANISM. A-197
papers in their " Transactions," and they seem to have looked upon his
speculations and experiments as scarcely worthy of notice. They
thought them the silly dreams of an ignorant provincial.1
Fortunately, however, for science and mankind, Collinson was more
intelligent, and saw at once
the value of Franklin's re-
searches. He published the
letters, and they drew the
attention of Europe. Buffon
read them in France, and
persuaded his friend Dali-
bard to translate them into
French ; Franklin's rare and
beautiful experiments were
repeated in Paris; Louis
XV and all his court has-
tened to see them, and were
charmed and amazed at
Franklin's genius and the
wonders of the new science ;
public lecture-rooms were
opened for their perform-
ance, and all Paris thronged
to the rare exhibition. The
letters were translated into
many languages, and sud-
denly the name of the ob-
scure printer in Philadelphia
became one of the most re-
nowned in the annals of
science. His theories were
assailed by the Abbe Nollet
and a party of the French
philosophers, but they also
found many defenders, and
a large school of enthusi-
astic men of science, struck
by the vigor of Franklin's
genius and the novelty of
Franklinists.
Still, however, Franklin's most daring speculation as to the unity
of the electricity of the earth and the air, which had awakened the
derision of the whole Royal Society, remained untested by experiment,
and the philosophers prepared, with doubt and dismay, to attempt its
1 Sparks's Life of Franklin, vol. v, p. 175.
Fig. 8.—Engraving of Benjamin Franklin's
Electrical Machine, the Oldest Improved
Form for Producing Electricity for Ex-
perimental Purposes.
his discoveries, assumed the name of
A-198
BLEYER.
verification. He felt that his fame must rest upon his success. If he
could draw down the lightning from the skies by presenting his iron
points to the thunder-cloud, he must attain a renown that would live
forever. If he failed, by the incompleteness of his instruments or any
unlooked-for accident, he would seem to merit the scorn which European
philosophers were prepared to pour upon him.
Philadelphia, too, offered no convenient tower or steeple on which to
fix his iron points ; while the modest inquirer was probably anxious that
his first experiment should be made with no one present to witness his
possible failure.1 His inventive mind suggested a simple expedient.
He formed a common kite from a silk handkerchief stretched upon
two crossed sticks; on the upper part was placed the iron point; the
string was of hemp, terminating in a short silken cord, and at the end
of the hempen string hung an iron key. Such was the simple appa-
ratus with which the philosopher set forth from his home, on a cloudy
day in June, 1752, to draw the lightning from the skies ; to penetrate a
mystery upon which ages had meditated in vain. He took his son with
him as the only witness of his secret adventure. As the rain was falling
he stood under a shed and raised his kite. It was, no doubt, a moment
of strong and unprecedented excitement, and we can well imagine that
Franklin watched his kite slowly ascending with a keener interest than
Etruscan augur or Roman priest had ever felt as he awaited the omen of
the gods. A cloud passed over, no trace of electricity appeared ; the
heart of the philosopher sank with dismay. But suddenly the falling rain
made the hempen string an excellent conductor, and Franklin saw that
its fibres began to be stirred by some unusual impulse. He applied his
hand to the key, and at once drew sparks from the skies. He felt that
he had triumphed; but the first thought of his generous nature, no
doubt, was how to make his discovery useful to mankind; and one can
scarcely avoid lamenting that no vision reached him, in the moment of
his victory, of that wonderful instrument with which another American
philosopher has girdled the earth and made electricity the guardian of
civilization.
Before his own success, Franklin's theory had already been tested
and proved in Europe.2 The French king, Louis XV, was a strong
Franklinist, and urged Buffon and the other philosophers to try the ex-
periment of the iron points, according to Franklin's directions. On the
10th of May, therefore, Dalibard erected a bar of iron forty feet long, at
Marly, and succeeded in drawing electricity from a thunder-cloud. It
should be remembered, too, that the Abbe Nollet had suggested the con-
nection between lightning and electricity before Franklin wrote ; and
that the idea had arisen in the minds of other philosophers. Yet
Franklin could not have been acquainted with their theories, and no one
1 Sparks's Life of Frnnklin, vol. v, p. 175.
8 Gentleman's Magazine, 1752, p. 229.
GALVANISM.
A-199
before him had ever suggested any means of forming a connection
with the thunder-cloud. His theory and his method were altogether
original.
Again Europe was startled by a novel thrill of wonder and excite-
ment.1 The electric sparks of the Abbe* Nollet and the famous ex-
periment of Leyden sank into insignificance before the sublimity of the
new achievement. Franklin, the modest philosopher of half-savage
America, snatching the thunder-bolt from the skies with his kite and
key, was the wonder of the hour. Kings became his disciples ; princes
flew kites in summer showers, and repeated the experiments ; Europe
was covered by a chain of iron points from Paris to St. Petersburg; and
the study of the lightning became as universal as in the days of Etruscan
superstition.
Franklin was covered with honors. The Royal Society of London,
eager to repair its former neglect, elected him a member and awarded
him its highest prize. In France, Russia, Germany, he was still more
highly honored; he was the most famous of philosophers. From this
time, too, until near the close of the century, the science of atmospheric
electricity was studied by eager observers. The thunder-cloud was the
favorite subject of learned inquiry. Brilliant hopes of further discoveries
were entertained that were never fulfilled ; and one eminent philosopher
fell a victim to the dangerous research.
Professor Richman, of St. Petersburg, had erected an iron rod in
his observatory for the purpose of repeating the American experiments,
and ventured too near the instrument; a sudden flash descended the
conductor, struck him upon the head,and passed through his body. He
fell dead against the wall. He is remembered as the martyr of the sci-
ence. Professor de la Garde, of Florence, was struck down by an unex-
pected shock, but recovered.2 Yet danger seemed only to add new
interest to the attractive study. Franklin invented his lightning-rod,
which was at once employed to protect the homes and the public buildings
of Europe and America; and his disciples were everywhere engaged
with kites and points in an effort to disarm the thunder-bolt of its
terrors.
The thunder-cloud was mapped out and described by countless ob-
servers. Lightning from its different forms was given different names.
Franklin and his innumerable disciples began now to extend their
researches over the whole domain of nature, and were rewarded by an
infinite number of novel discoveries. Everywhere electricity was found
to be capable of explaining mysteries that had long seemed supernatural
and almost divine, and of offering attractive theories that served to
delight and inspire the fancy, even if they did not wholly satisfy the
reason. The auroral lights that danced in lovely variety over the icy
1 Acad, des Sciences, 1752, p. 9.
* Gentleman's Magazine, 1753, p. 432.
A-200
BLEYER.
fields of the north were believed to be electrical.1 Castor and Pollux,
or the baleful Helen, who had wreathed their spectral forms around the
masts of Roman ships, now created to be supernatural; the luminous
rains, where every drop seemed a ball of fire, or the strange flames that
sometimes hovered over armies as they went to battles, were found to be
no more mysterious than the Leyden jar ; the fearful roar of the thunder
was known to be only the echo of the first discharge among the piles of
clouds ; the electric fire was traced to the water-spout, the whirlwind, or
the crater of the volcano ; and the triumphant inquiries at length dis-
covered that the round world itself was only a huge electrical machine,
and that all its tenants were constantly influenced by the subtle changes
of the electric atmosphere.
It was soon observed that the human body was strongly influenced
by the electric discharge; the blood ran quicker, the limbs were stirred,
the spirits were excited, the intellect aroused ;2 and enthusiastic phy-
sicians recorded wonderful cures performed by the aid of electricity.
Had not a panacea been discovered ? Was not this strange spiritual sub-
stance nearly allied to the source of life ? The idea, in the last century,
excited a new thrill of expectation and awe. Electricity was applied to
various forms of disease, and was afterward found successful in effecting a
cure. It augmented the circulation of the blood, increased the pulsa-
tions, and improved digestion. The paralytic were healed and made to
walk again; the feeble and depressed seemed inspired with new hope.
The dumb were made to speak, and the blind see.3 Bertholon, who
wrote a treatise on medical electricity toward the close of the last cen-
tury, relates numerous instances of cure performed by its aid, and the
scientific world was full of hope in the efficacy of their new medicament.
The electrical machine, for a time, seemed ready to alleviate the worst
forms of human woe. So sanguine are men of coming good, so eager to
escape from present pain 1 Yet the pleasing medical dream soon passed
away, and it was found that even the Leyden jar was incapable of repair-
ing the ravages of disease, or of amending those evils which men, by
their own excesses, so often bring upon themselves. The dissolute noble
still fell down in a paralytic fit from which even the skillful electrician,
Abbd Nollet, could never awaken him ;4 the uncleanly city was still full of
pestilence; the poor hovel communicated its fevers to the palace.
Electricity of to-day, bridled as it is in the hands of the modern
scientist and physician, brings forth more ripened fruits. Many ail-
ments are now amenable to the current where other medical agents have
failed. The doctor of this age has done mudh toward bringing electro-
therapy to the front rank of medical science.
1 De la Rive, Treat. Elect., iii, p. 169.
3 Bertholon, De l'Electricite du Corps Humain, etc., i, p. 94 etseq.
'Several cases of dumb persons being cured are related in the papers of the time. See
Gentleman's Magazine. 1752 and 1753.
4 Bertholon, i, p. 440. Nollet was the first to electrify the paralytic.
GALVANISM.
A-201
This medical thunder-bolt (electricity) has passed through many
vicissitudes, being at one time recognized and employed at the various
hospitals, and then again being thrown aside and left for the most part
in the hands of the money-making charlatans and quacks; though, as
each new important discovery in this science has been reached, medical
men's minds have again turned anew to the subject, and interest in its
therapeutic properties has been awakened. But as every tide has an ebb
and a flood, so the promises of cure; there have followed failures and
disappointments which have thrown the usage of this valuable agent
into disrepute, to be again, after a time, reborn and nursed into popular
favor. It was during a period of two hundred years in which these
alterations have been taking place, in the opinions held of the value of
electrical treatment and in the frequency of its employment. Men of
science have unceasingly been pursuing their investigations into its
wonderful mysteries, properties, and possibilities. New successful re-
search on new research has been their patient reward, and to-day we have
arrived at an age when practical electricity is making most rapid strides.
We shall see, also, the day when the current will be meted out to the
suffering in such dosage as our present remedies are meted. The time
has arrived, and another electro-therapeutic cloud is hanging over the
medical world again. In the past few years special didactic and clinical
departments have been added to the regular college curriculum in many
of the foremost institutions. The current is once more called into service
to aid in the conquering of the many maladies that physicians and sur-
geons are battling with. It seems that a general desire has been evinced,
both by members of the profession and the laity, for a more thorough
knowledge of the benefits to be derived from this agent, electricity, and
the best means of securing them.
One of the most astonishing discoveries, to the intellect of this age,
was the explanation now given of the wonderful properties of the
torpedo and the electric eel. They were soon shown to be natural
Leyden jars. The torpedo had been noticed by Aristotle and Pliny, and
had long been an object of wonder and superstitious dread to the fisher-
men of the Mediterranean. But its electric power was feeble compared
to the startling shocks conveyed by the gymnotus of the lagoons of
Cayenne and South America. Humboldt has given a striking descrip-
tion of the vigor of this most famous of the electric fish.1 He had been
anxious to obtain living specimens of the gymnotus, and employed a
number of the natives of the country to engage in the singular fishery.
The gymnotus lives in the hot bayous of Cayenne, covered by the thick
shade of tropical vegetation and hidden in the muddy waters. It is
often more than five feet in length, and its electric shocks are so power-
ful that no living thing ventures to invade its retreat. Even the Indians
are afraid to strike it with harpoons or to catch it with a line, since
1 Travels, vol. ii, pp. 113,114.
A-202
BLEYER.
its powerful discharges benumb their arms and drive them away in
terror, while the serpent-like agility of the great eel enables it to elude
or destroy their nets. Humboldt, together with a party of natives,
approached a lagoon inhabited by the electric monsters. He could not
conceive how the Indians were to succeed in taking their prey alive;
they told him, to his surprise, that they were about to fish for them with
horses. A number of mules and horses were collected on the banks of
the lagoon, and the Indians drove them, with blows and loud outcries,
into the dangerous waters. A strange battle at once began. The elec-
tric eels, roused from their torpor, attacked the unfortunate invaders,
fastening upon the lower parts of their bodies and giving them a
succession of almost fatal shocks. Benumbed, terrified, and fainting,
they strove Jfco fly from the dangerous pool, but the Indians drove them
back again with wild cries and sharp blows, and the co'mbat was renewed.
The huge eels were seen rushing to assail their foes with fresh vigor, and
the savages, clinging to the overhanging trees and bushes, forced the
horses into the midst of the water ; and at length, in a few minutes, the
battle was decided, and several of the horses sank and were drowned.
" The contest," says Humboldt, " between animals so different in organ-
ization, in so strange a place, presented a most picturesque spectacle."
It must certainly have been a painful one. And now the victorious eels,
having exhausted all their electricity, crept languidly toward the shore,
where they were taken with small harpoons fastened to dry lines. So
completely was their power lost that the Indians did not receive a shock.
Humboldt secured several eels, but little injured, more than five feet
long, and he was told that they were often much larger. It is a peculiar
trait of the electric animals that they are produced in water,—an excel-
lent conductor,—and that, by some natural provision, they can discharge
or retain their electricity at pleasure.
Philosophers now began to explain them with attention, and to form
theories as to the source of their action. But the production of animal
electricity seems capable of being explained only by those later theories
which were soon to enlarge and adorn the science.
Thus the eighteenth century had elevated electricity into one of the
most important and attractive branches of knowledge; it was reserved
for the nineteenth to apply it practically to the benefit of mankind. In
all his brilliant and thoughtful experiments, Franklin had often sighed
over their apparent uselessness : he would have been amply satisfied
could he have foreseen how powerful an agent his favorite science was
destined to become in advancing manufactures and the arts, and in
binding nations together by an almost instantaneous exchange of thought.
Galvanism, the next great step in electrical progress, was discovered
by Galvani, Professor of Anatomy at Bologna, about the year 1790.1
1 Becquerel, vol. i, p. 83. See report Historique sur les Progres des Sciences Mathe-
matiques, Paris, 1810, p. 224.
GALVANISM. A-203
A circumstance so accidental as the slight illness of Madam Galvam
gave rise to this important event. Her physician had recommended her
to a diet of frog-broth, and several of the animals, prepared for the cook,
chanced to lie on a table near an electrical machine. One of Galvani's
assistants drew sparks from the conductor, and Madam Galvani was sur-
prised to observe that when he did so the muscles of the frogs were dis-
torted and assumed the appearance of life. She called Galvani to notice
the strange circumstance. The experiment was repeated with success,
and the philosopher, who knew little of electricity, but was a careful
anatomist, believe'd he was on the brink of discovering the principle of
life. He entered with strange
ardor upon the new research.
He experimented incessantly
upon muscles and nerves. At
length he found that muscles
and nerves were thrown into
the singular convulsion by the
mere presence of two different
metals, and had discovered by
accident the principle of gal-
vanism,— the source of the
magnetic telegraph or the
calcium light.
Still, however, Galvani
persisted in his scientific de-
lusion that he had unfolded
the origin of being. He in-
sisted that the muscles and
the nerves created the electric action. He overlooked the effect of the
two metals. His disciples were soon numerous, and all Europe was again
aroused into excitement by the unparalleled disclosures that philosophy
seemed about to make.
Electricity had but lately been drawn down from the clouds; the
whole earth was shown to be electric ; with one stride more the daring
science might unfold the whole mystery of being. But, fortunately for its
success, galvanism was taken from the control of its speculative discoverer,
and fell into more practical hands. Volta, Professor of Natural Philos-
ophy at Como,an excellent electrician, assailed the theory of his colleague,
and showed that the galvanic action came from the two metals, and not
from the nerves. A violent controversy raged between the Bolognese
school of Galvani and the followers of Volta, and the important question of
the origin of life was discussed by the philosophers and the people while
Napoleon was preparing to cover Europe with carnage, and while the
horrors of the Parisian massacres were yet fresh in every mind. The
" reign of terror " which had been commenced in France was about to
Fig. 9.—Experiment with Frog.
A-204 BLEYER.
extend over all European civilization when the two Italian philosophers
were marshaling their disciples in a vigorous intellectual combat. Volta
was victorious, and his peaceful triumphs will outweigh a thousandfold,
in its beneficial consequences, the disastrous successes of Napoleon.
In the year 1800, a memorable epoch in the history of electricity,
Yolta announced to the world, in a letter to Sir Joseph Banks, his in-
vention of a wonderful machine. It was composed of alternate sheets
or layers of zinc and copper, separated from each other by discs of wet
cloth. Two streams of electricity, one negative and the other positive,
were found to flow from either pole of the instrument, and its intensity
could be increased apparently without limit by enlarging the number of
layers. He had invented a voltaic pile. Its form was afterward changed
by substituting cups of zinc instead of layers, and Volta formed a beau-
tiful apparatus called " La Couronne de Tasses," the model of all those
Fig. 10.—Couronne de Tasses.
powerful instruments by which the electric current is dispatched on its
useful mission from New York to San Francisco, or taught to fathom
the once impassable Atlantic. The wonderful vigor of the new agent
became at once apparent. The sharp sparks of Franklin's electrical
machine, and even the condensed shock of the Leyden jar, so long the
terror of philosophers, were found to be faint and inefficient compared
with the mighty electric current that flowed with silent strength from
one wire to the other of the voltaic pile. Its effect on the human frame
revived Galvani's notion of the principle of life. When the hands of the
operator were applied to the opposite poles, instead of a sudden shock he
found himself held in the grasp of an invisible power. A series of strono-
convulsions ran through his arms and shoulders. Scarcely could he
withdraw his hands and free himself from his captor. If the instrument
were applied to the forehead, a brilliant light flashed over the sight, even
though the eyes were closed. The glow-worm touched by the current
GALVANISM. A-205
shone with increased splendor ; the grasshopper chirped as if excited by
a stimulant. But when the pile was applied to the trunk of a decapitated
body, a most horrible and unheard-of phenomenon occurred. Never had
such a spectacle been witnessed before since the age of miracles. The
dead body rose from its recumbent position; its arms moved as if to
strike in its rage objects in its vicinity ; its breast heaved, its legs re-
covered their strength; and life was imitated or renewed in its fearful
actions. Such were some of the tales told over Europe of the powers of
the voltaic pile.
It was an age of excitement. Napoleon, the young conqueror of
Austria and Italy, now ruled as First Consul at Paris. The revolution
had died to give place to a reign of war and violent convulsion.; and
Napoleon, the centre and source of the impending disturbance, yet always
eager for scientific novelty, invited Volta to Paris to explain his new
instrument.
In 1801, crowned with his peaceful victory, the Italian philosopher
visited the republican court. At three meetings in the. Academy of
Sciences, in the presence of Napoleon and the most famous philosophers
of France, Volta lectured upon his incomparable discovery. He was
crowned with the highest honors of the institute; Napoleon loaded him
with gifts and attentions, selected galvanism as his favorite branch of
science, and offered a reward of sixty thousand francs to him who should
produce in electricity or magnetism an impulse equal to that which had
followed the invention of the voltaic pile, or the startling experiment of
Franklin.
Of all the excitements of the age none stirred the intellect more
strongly than Yolta's theories. The voltaic pile was believed to, be the
frame-work of the living organization. Napoleon and his philosophers
were struck and impressed by the wonderful .idea. " It is the image of
life !" said the imperious young conqueror, as he once watched some
remarkable experiments.1 The brain was supposed to be an electric
pile, the nerves and muscles the conductors of opposing currents, and
the slow beating of the heart the effect of their united action. In
moments of fierce excitement positive electricity flashed from the eyes
and stirred the nerves ; in periods of repose the negative controlled the
system. Rage, valor, and achievement were positive; submission and
cowardice the current from the opposite pole. On the battle-field the
fierce conqueror, a terrible voltaic battery, flashed forth his electric cur-
rents in fatal profusion ; his opponent yielded because his galvanic vigor
had declined. The world dreamed wildly over the new machine, and
men, with their usual vainglorious presumption, believed themselves gods.
The dreams were swiftly dispelled; but a series of valuable dis-
coveries followed rapidly the invention of the voltaic pile. The first
twenty years of the present century were made illustrious by the achieve-
1 Lardner, vol. i, p. 113.
A-206 BLEYER.
ments of the new machine. A splendid throng of eminent chemists and
electricians sprang up under its influence, and pursued with intense labor
and wonderful discoveries the path pointed out by Volta and Galvani.
France, England, Germany, Europe, and America united in advancing
the science ; and the names of Oersted and Ampere, Davy and Wollaston,
Berzelius and a great company of men of genius, scarcely inferior to their
leaders, won a renown in their peaceful pursuit that shines with a softened
glory amidst the fierce military excitement of that troubled age. Of
these men Humphry Davy was perhaps the most conspicuous. Poet,
thinker, philosopher, Davy finally concentrated all the great powers of
his intellect upon the study of the voltaic pile. He used it to unfold the
deepest mysteries of nature. He discovered its wonderful strength,
and developed all its resources. Suddenly the most solid and least
fusible substances in nature were found to melt awa}r into gases before
the steady flow of the galvanic current. Water resolved itself into its
gaseous elements. The alkalies liquefied and left behind them their me-
tallic bases. New metals were discovered whose existence had never
been suspected. A tremendous heat was produced that burned gold and
silver as easily as paper, and that even fused the firm platinum.1 A
magnificent light was produced by burning potash, such as man had never
created before. The diamond was melted ; the various earths dissolved ;
the composition of the air investigated ; and it was believed that all the
geological changes of the surface of the globe were to be attributed to
galvanic action. In fact, chemistry became almost a new science under
the reforming influence of the voltaic pile ; and the brilliant researches
of Sir Humphry Davy and his associates astonished their age by their
singular novelty and their rare value to the artist and the machine.
Thus the dawn of the nineteenth century might seem to have been
almost consecrated to the study of the electric forces. Yet it was also
a period of unusual intellectual excitement; and while Davy, Oersted,
Ampere, and their associates were startling the world by a succession of
wonderful discoveries, the literary atmosphere resounded with the strains
of a new school of poetry. Byron, Moore, Coleridge, Wordsworth, and
Keats poured forth the language of passion or of reflection to countless
readers, and literature united with science in aiding the progress of
thought.
At length, in 1820, Oersted, by a remarkable experiment, found the
indissoluble union between magnetism and electricity. The magnet, as
well as the electron, had long been one of the chief mysteries of nature.
Thales had observed its attractive properties, and had supposed that it
was endowed with a soul. The Chinese and the Arabs knew that the
magnetized needle invariably pointed to the north, and had employed it
to guide their journeys by land or sea. Its variations were observed by
Columbus, and studied with attention by the early Dutch and English
1 Lardner, i, p. 133.
GALVANISM.
A-207
navigators. Its connection with electricity had for some time been sus-
pected, and Franklin magnetized a needle by an electric discharge.
But it is to Oersted that we owe the grand experiment by which it
was shown that the motion of the magnet depended upon galvanic cur-
rents. He showed that a magnetized needle was deflected or controlled
by the passage of the electric fluid along a wire. The discovery pro-
duced a new ardor in every scientific mind. Ampere, Arago, Davy,
Faraday, and Henry enlarged upon the thought; powerful magnets were
formed by passing the voltaic fluid through a wire bound in spiral folds
around an iron bar, and the principal ones at length discovered upon
which rests the crowning achievement of electricity,—the magnetic
telegraph !
We have now traced, though very briefly, the progress of knowledge
of electricity, from the germ of the science which lay hidden for thousands
of years in amber, like the insects so"often found in that substance,—
and yet unlike them, for it possessed immortality,—up to the first prac-
tical application of that knowledge to human use and benefit. The
lightning had been caged. The mighty force, which since the creation
of mankind had aroused but feelings of awe and terror, could now be
confined and examined, or diverted at will from its path of destruction.
The wise men of the eighteenth century had captured the electrical
Pegasus ; it remained for the wiser men of the nineteenth century to
yoke him to the plough.
It is the most poetical of the sciences, as well as the most practical.
Its future is full of promise, and no one can safely affirm that it may not
yet achieve discoveries more wonderful than any in the past, and pro-
duce a still more beneficial effect upon the progress of man. Yet its
earlier cultivators can never be forgotten, and the gratitude of their race
must always attend those laborious intellects whose endless toil snatched
the thunder-bolt from the skies and made it the useful servant of modern
civilization.
Electrical Measurement.
Twenty-five years ago the experimental sciences of electricity as
well as magnetism were, in great measure, mere collections of qualitative
results, and, in a less degree, of results quantitatively estimated by
means of units which were altogether arbitrary. These units, depending
as they did on constants of instruments and conditions of experimenting
which could never be made fully known to the scientific public, were a
source of much perplexity and labor to every investigator, and to a great
extent prevented the results which they expressed from bearing fruit to
the furtherance of scientific progress. Now, happily, all this has been
changed. The absolute system of units introduced by Gauss and Weber,
and rendered a practical reality in England by the labors of the British
Association Committee on Electrical Standards, has changed experi-
A-208 BLEYER.
mental electricity and magnetism into sciences of which the very essence
is the most delicate and exact measurement, and enables their results to
be expressed in units which are altogether independent of the instruments,
the surroundings, and the locality of the investigator.
The record of the determinations of units made by the members of
the committee, for the most part of the methods and instruments which
they themselves invented, forms alone one of the most interesting and
instructive books1 in the literature of electricity, and, when the history
of electrical discovery is written, the story of their work will form one
of its most important chapters. But besides placing on a sure founda-
tion the system of absolute units, they conferred a hardly less important
benefit on electricians by giving them a convenient nomenclature for
electrical quantities. The great utility of the practical units and nomen-
clature which the committee recommended soon became manifest to every
one who had to perform electrical1 measurements, and has led, within the
last few years, to their adoption, with only slight alterations, by nearly
all civilized nations. Although it is only five years since the recom-
mendations2 of the Paris Congress of Electricians were issued, they have
been almost universally adopted and appreciated by those engaged in
electrical work, and have thus begun to yield excellent fruit by rendering
immediately available for comparison, and as a basis for further research,
the results of experimenters in all parts of the world.
But in order that the full benefit of the conclusions of the Paris
Congress may be obtained it is essential, in the first place, that conve-
nient instruments should be used ; adapted to give directly, or by an easy
reduction from their indications, the number of amperes of current flow-
ing in a particular circuit, and the number of volts of difference of
potential between any two points in that circuit. To be generally useful
in practice these instruments should be easily portable and should have
a very large range of sensibility,; so that, for example, the instrument
which suffices to measure the full potential produced by a large dynamo-
electric machine may be also available for testing, if need be, the
resistance of the various parts of the armature and magnets by the
readiest and most satisfactory method, namely, by comparing, by means
of a galvanometer, a high resistance of difference of potential between
the two ends of a known resistance joined up in the same electrical cir-
cuit. In like manner the ampere measure should be one that could be
introduced without sensible disturbance into a circuit of low resistance
to measure either small fractions of an ampere or the whole current
flowing through a circuit containing a large number of electric lamps.
These conditions are more or less fulfilled by a large variety of practical
instruments recently patented by different inventors.
1 Report of the British Association Committee on Electrical Standards. Edited by Pro-
fessor Jenkin, F.R.S.
3 See Appendix, in book on Absolute Measurements in Electricity and Magnetism, by
Andrew Gray, M. A., F.R.S. E., for practical units, as adopted by the British and Paris Associa-
tions. London : Macmillan & Co.
GALVANISM.
A-209
Almost every branch of science nowadays has its own language,
made up of its technical terms, which in time become absorbed even into
general speech. This is already fast becoming the case with the language
of electricity. Amperes and volts and ohms are no longer possessed
of meaning only to the initiated, but are taking their place among such
every-day standards as pounds and gallons and inches. Although this
chapter has none of the pretensions of a treatise, it is my aim to devote
it to a plain statement of the principles of electrical measurement and
the uses of the most important forms of the galvanometer.
There is no force in nature more subject to the inevitable laws of the
great mother than electricity ; and many of these laws, and these meas-
urements dependent upon them, are so simple as with little study to be
readily mastered. Just as in the ordinary arithmetical standard we
employ weights and measures, so we may in the application of electricity
employ various measurements for various purposes.
As, also, we commonly employ suitable instruments and apparatuses
in weighing and measuring tangible substances, using scales or balances
for those bought and sold by weight, tape-measures and miles for meas-
urements, and clocks and watches to mark the advance of time, so we
find it essential, in the valuations and comparisons of electricity, to use
suitable instruments.
These instruments are named galvanometers, and are used to measure,
compare, and estimate many of the different properties and magnitudes
of electricity. By their aid we may readily ascertain and compare the
working strength and value of electric currents, the resistance which
electro-magnets, wires, and other conductors offer to the passage of the
current, the electro-motive force or initial power, and the resistance of
batteries, etc. Farther on we shall speak in full of the galvanometer, etc.
Definitions of Electrical Terms and Units.—In order that the gal-
vanometer be clearly understood, as well as when, why, and how to use
it, it is proper that at the outset we should at least have some compre-
hension of the meaning of the terms commonly used in expressing the
different properties, magnitudes, functions, and relations of electricity
and electrical conductors, and of the units which indicate the value of
such properties.
In the part of this work on " General Remarks upon Batteries," I
have already given in detail, and shown by means of experimental illus-
tration, some of these electrical terms, such as electro-motive force,
potential, resistance, joint resistance, internal resistance, etc.
Units of Electrical Measurements.—We know now, by what has
been seen, that the batteries by which electricity is developed, the con-
ductors by which it is transferred, the instruments by which it is made
useful, and the electric current itself have certain properties, magnitudes,
or qualities which it is often necessary to measure in order that their
working value may be properly estimated.
14
A-210
BLEYER.
In order to make such measurements and to state their results, it is
essential that there should be some standard terms or units, which, when
expressed, will convey to the mind definite ideas, precisely as in meas-
uring a distance, etc.
Furthermore, when one substance has several properties or magni-
tudes, a different system of measurement is required for each magnitude;
for, as in a cubic block of wood we should measure one of its sides by
superficial measure, its contents by cubic measure, and its weights by still
another system, and would state the results differently in each case, so
the different electrical magnitudes have their own opposite and separate
units in which the results are expressed.
Sometimes it is found that the results of certain measurements are
obtained by reference to several different magnitudes; as, for example,
when the time is taken of the speed of a horse, or a locomotive, we take
the length of the distance traversed and the time consumed in traveling
that distance, and so calculate the velocity by reference to both space
and time. In certain electrical measurements we find it necessary to
resort to the same process, and to combine different units to obtain a
definite result.
The names of distinguished electricians and scientists have been
given to the practical electrical units. Thus the unit of electro-motive
force is called the "volt," from Yolta; and the unit of resistance the
" ohm," after Ohm, the German physicist and mathematician; while the
unit of current-strength is named the " ampere," after the French phi-
losopher.
An Analysis of the Arithmetical Electrical Terms.—Space is the
lineal distance from one point to another.
Time is the measure of duration.
Force is any cause of change of motion of matter. It is expressed
practically by grammes, volts, pounds, or other units.
Resistance is a counter-force or whatever opposes the action of
force.
. Work is force exercised in traversing a space against a resistance or
counter-force. Force multiplied by space denotes work as foot-pounds.
Energy is the capacity for doing work, and is measurable by work
units.
Mass is quantity of matter.
Weight is the force" apparent when gravity acts upon mass. When
the latter is prevented from moving under the stress of gravity its weight
can be appreciated.
Physical and mechanical calculations are based on three funda-
mental units of dimension, as follow : the unit of time, the second,__T ;
the unit of length, the centimetre,—L ; the unit of mass, the gramme,—M.
Concerning the latter, it is to be distinguished from weight. The gramme
is equal to one cubic centimetre of water, under standard conditions, and
GALVANISM.
A-211
is invariable. The weight of a gramme varies slightly with the latitude
and with other conditions. Upon these three fundamental units are
based the derived units,—geometrical, mechanical, and electrical. The
derived units are named from the initials of their units of dimensions,
the C. G. S. units, indicating centimetre, gramme, second units.
In practical electrical calculations we deal with certain quantities
selected as of convenient size, and as bearing an easily-defined relation to
the fundamental units. They are called practical units.
The cause of a manifestation of energy is force ; if of electro-motive
energy,—that is to say, of electric energy in the current form,—it is
called electro-motive force (E. M. F., or simply E.), or difference of po-
tential (D. P.). What this condition of excitation may be is a profound
mystery, like gravitation and much else in the physical world. The
practical unit of electro-motive force is the volt, equal to one hundred
millions (100,000,000) C. G. S. units of electro-motive force. The last
numeral is expressed more briefly as the eighth power of 10, or 108.
Thus the volt is defined as equal to 108 C. G. S. unit of electro-motive
force.
This notation in powers of 10 is used throughout C. G. S. calcula-
tions. Division by a power of 10 is expressed by using a negative expo-
nent, thus 108 means xo-o^ffo-ouo"- The exponent indicates the number of
ciphers to be placed after 1.
When electro-motive force does work, a current is produced. The
practical unit of current is the ampere, equal to y1^ C. G. S. unit, or
101 C. G. S. unit, TXo being expressed by 101.
A current of 1 ampere passing for one second gives a quantity of
electricity. It is called the coulomb, and is equal to 101 C. G. S. unit.
A coulomb of electricity, if stored in a recipient, tends to escape
with a definite electro-motive force. If the recipient is of such character
that this definite electro-motive force is 1 volt, it has a capacity of 1
farad, equal to too"oooo"o~o"5 or ^9 C* ^- ^- un't.
A current of electricity passes through some substances more easily
than through others. The relative ease of passage is termed conduct-
ance. In calculations its reciprocal, which is resistance, is almost uni-
versally used. A current of 1 ampere is maintained by 1 volt through a
resistance of 1 practical unit. This unit is called the ohm, and is
equal to 109 C. G. S. unit.
Sometimes, where larger units are wanted, the prefix deka, ten
times ; heka, one hundred times ; kilo, one thousand times ; or mega, one
million times, is used,—as dekalitre, ten litres; kilowatt, one thousand
watts ; megohm, one million ohms.
Sometimes, where smaller units are wanted, the prefix, deci, one-
tenth ; centi, one-hundredth; milli, one-thousandth; micro, one-mil-
lionth, are used. A micro-farad is one-millionth of a farad.
Practical Units.—Electro-motive force is measured in volts. A
A-212
BLEYER.
volt is very nearly the pressure yielded by a certain standard galvanic
cell, usually the Daniell, to be described later in this work. The term
has also a very accurate mathematical signification.
The " volt " is the unit of electro-motive force, and has very nearly
the same value as a single cell of the Daniell battery. Its precise value
is 9268 of a Daniell cell in good condition ; in other words, the Daniell
cell is equal in electro-motive force to one volt and seventy-nine thous-
andths—1.079. The volt is equivalent to the electro-motive force re-
quired to produce a current of the strength of 1 ampere in a circuit
having a total resistance of 1 ohm.
The electro-motive force of most of the gravity batteries is almost
the same as that of the Daniell, and the electro-motive force of the
Leclanche cell is 1.481, or one volt and four hundred and eighty-one
thousandths.
OHM'S LAW AND ITS EXPLANATION.
The law showing the relation between electro-motive force, resist-
ance, and current was enunciated by Dr. G. S. Ohm, and is known as
Ohm's law. This is the fundamental law of electricity in motion.
Consequently, there are three things about any electric current to
be known, namely : its electro-motive force, or pressure ; the resistance
which it encounters; and the strength of the current, which depends
upon these.
We measure steam- or water- pressure in pounds per square inch,
heat by thermometric degrees, distances by feet and inches, and so on.
The Ohm.—The standard unit of resistance, which we call the
" ohm," may be defined as a resistance about equal to that offered by a
wire of pure copper one-twentieth of an inch in diameter and two hun-
dred and fifty feet long, or it may be compared to one-sixteenth of a
mile of copper wire, No. 4^ Birmingham wire gauge, which is twenty-
three hundredths of an inch, or nearly a fourth of an inch in diameter.
It is also approximately equal to a piece of No. 35 copper wire between
seven and eight feet long. A mile of No. 12 galvanized-iron wire has an
average resistance of about 32 ohms.
The mark which may usually be found stamped on the base of a
relay denotes the resistance of the coil from one binding-screw to
the other. If, for example, we have a relay marked 100 ohms, we know
that that is the measured resistance of the two spools, and that it is
equal to about three miles of No. 12 galvanized-iron wire.
THE OHM'S LAW-GIVING SPECIFIC VALUE.
Thus, the strength of current in amperes flowing through a circuit
is equal to the number of volts of electro-motive force divided by the
number of ohms of resistance in the entire circuit. The strength of
current is ascertained by taking the electro-motive force in volts and
GALVANISM. A-213
dividing that number by the total resistance of the circuit, including that
of the battery, wires, and instruments, in ohms. The result will be in ■<
amperes, or fractions thereof.
Let us follow this problem out. A battery having an electro-motive
force of 50 volts and an internal resistance of 75 ohms is connected in
circuit with a galvanometer having a resistance also of 10 ohms. The
total resistance in the circuit is that of the battery, galvanometer, and
wire added together, i.e., 160 ohms. To find the strength of current we
divide the 50 volts by the 160 ohms, which gives us a quotient of 0.3125
ampere, or 312^ milliamperes.
Therefore, if we know the electro-motive force and resistance of any
circuit, we can easily figure out the strength of current. On the same
principle, knowing the electro-motive force in volts of a battery, and the
current in amperes produced thereby in a given circuit, we can ascertain
the resistance of that circuit, including that of the battery, by dividing
the electro-motive force by the current. Likewise, the value of electro-
a b
Fig. 11.
a, battery; b, electro-magnet; c, connecting wire.
motive force may be obtained if we know that of the current and of the
total resistance of the circuit; for if we multiply the resistance in ohms
by the current-strength in amperes, we find the value of the electro-
motive force in volts.
The Ampere.—The unit of current-strength was, until very lately,'
called a " weber," but is now called the ampere, after the French physi-
cist of that name. The ampere may be defined as the strength of a
current produced in a circuit having a total resistance of 1 ohm by an
electro-motive force of 1 volt.
Let us explain it in the following way : If a circuit consisting of
one cell of a battery, an electro-magnet, and the necessary connecting
wires, as in the above diagram,—the battery, we will suppose, having an
electro-motive force of 1 volt and an internal resistance of ^ ohm,—the
electro-magnet and connecting wires also have a resistance of ^ ohm
each, making a total resistance of 1 ohm in circuit.
The current flowing in this circuit will have a strength of 1 ampere.
A milliampere is one-thousandth of an ampere, and is made use of in
computing currents of comparatively feeble strength. This last unit of
current-strength is used in medical electricity.
A-214
BLEYER.
To recapitulate in briefer terms, electro-motive force means electrical
pressure. Resistance has its obvious meaning. Electro-motive force is
not measured in pounds per square inch like steam- or water- pressure,
but in volts ; and a volt is the pressure given by one standard cell.
Resistance is measured in ohms, and an ohm answers to the resist-
ance offered by four hundred and sixty feet of ordinary telegraph-wire.
Approximately, strength of current is measured in amperes. Speaking
of a water-wheel, we say we need current flowing at the rate of so many
gallons per minute to drive it; speaking of an electric lamp, we say
we need a current of from 1 to 50 amperes to keep it glowing. The
term "coulomb" is a unit current or ampere which transmits the unit
quantity of electricity in one second. The unit of electric quantity is
called a coulomb; and just as the unit flow of water through a pipe
might be taken as that which allowed one gallon of water to pass any
point in the pipe during one second of time, so the'ampere is the strength
of current—the rapidity of flow—which allows 1 coulomb to pass any
point in the circuit during one second ; so that if a constant current of
1 ampere has been flowing for one hundred seconds in a circuit, then we
know that 100 coulombs of electricity have passed any point in the
circuit during that time. This unit is far less employed in practice than
any of the others, but it may be, in the end, the most familiar of all; for,
as electro-therapists, we must sooner or later realize the necessity of
measuring the quantity of electricity we give our patients, just as we
do any other remedy in our pharmacopoeia; and when the electric light
comes into more general use in dwellings we shall pay for our electrical
supply at so much per thousand coulombs, as we pay for gas at so much
per thousand cubic feet.
Tables of Resistances and Conductivity.—It has been already stated
that the resistance of a conductor depends upon its dimensions and the
matter that composes it. Matthiessen, taking copper, found the following
values :—
Metal. Specific Resistance.
Silver,.............0.77.
Gold,.............1.38.
Aluminium,............2.29.
Zinc,.............2.82.
Iron,.............5.36.
Tin,.............6.76.
Platinum,............7.35.
Lead,.............9.96.
German silver,...........10.09.
Antimony,............18.07.
Mercury,............47.48.
Bismuth,............64.52.
Graphite,............1106.00.
Gas-carbon,............2037.00.
From this table we learn that, of all metals, silver offers the least
GALVANISM.
A-215
resistance. We can easily arrange a table of conductivity by taking the
reciprocals of the foregoing :—
Metal. Specific Conductivity.
Silver,.............100.00.
Copper,............77.43.
Zinc,.............27.39.
Iron,.............14.44.
Platinum,............10.53.
Lead,.............7.77.
Mercury,............1.03.
German silver,...........7.67.
Graphite,............0.0693.
Gas-coal,............0.0386.
The relative conductivity'of the principal liquids used in batteries
may be seen from the following values found by Becquerel (conductivity
of silver = 100,000,000) :—
Liquid. __ Conductivity.
Copper sulphate (a saturated solution),......5.42.
Ordinary salt " " " ......31.52.
Copper nitrate " " " ......8.99.
Zinc sulphate " " " ......5.77.
20c.c. of H2S04 in220c.c. water,.......88.68.
Nitric acid,............93.77.
Resistances of liquids at different stages of concentration may
be seen from the following table by Wiedemann (resistance of plati-
num = 1) :—
Sulphuric Acid Contained in 100 C.c. Water. Resistance.
3.7 grammes,...........499,000.
5.9 " ...........283,500.
11.42 " ...........147,200.
22.82 " ...........88,070.
45.84 " ...........79,560.
74.83 " ...........108,300.
183.96 " ...........508,000.
With salt solutions the resistance diminishes as the amount of salt
increases, the conductivity of pure water being very small. The be-
havior of sulphuric acid is peculiar. Up to a certain point resistance
diminishes with the increase of concentration, but beyond this point
resistance increases with further concentration.
The influence of temperature upon a liquid may be seen from the
following table, after Wiedemann. The liquid tested was formed by
solution of 187.02 grammes of copper sulphate in 1000 cubic centimetres
of water:—
At 20.2° C,........the resistance = 1,907,000.
At 26.2° C.,........" " —1,715,000.
At 37.5° C.,........" " =1,419,000.
At 51.5° C,........" " =1,163,000.
At 60.0° C.,........" " =1,047,000.
At 75.6° C,........" " = 894,000.
A-216
BLEYER.
The resistance diminishes as the temperature increases, a result
which is exactly opposite to what occurs with metals. Muller found
the following values for copper wire at different temperatures :—
At 21° C.,.........the resistance = 864.
At a dull-red heat,......." " =2100.
At a red heat,........" " =2450.
At a bright-red heat,......." " =3300.
At a white heat,........." " =4700.
When the wire was again cooled to 21° C. its resistance was 910.
Conductivity for carbon increases with the temperature, thus agree-
ing with the action of liquids. Professor Ayrton thinks this seems to
indicate that carbon may be a compound, and not an element. Mercury
follows the other metals; that is, conductivity decreases and resistance
increases with temperature.
The Wheatstone Bridge is the differential resistance measurer. This
instrument is fully described by Wheatstone, its inventor, in the " Trans-
actions of the Royal Society," 1843. This bridge, or also called elec-
trical balance, is usually constructed in this manner: Upon a piece of
well-seasoned board, M, are placed three strips of thin brass or copper
about half an inch in width, which are fastened as shown at A, B,and D,
a break being left at both ends of A, and also between B and D. From
B to D a thin German-silver wire, which should be uniform in thickness
and free from flaws, is stretched and soldered to the brass or copper
strips at each end. Underneath this wire a paper scale, accurately
divided into a thousand parts, is placed. Should the length of the wire
be, as is usually the case, a metre, the divisions will, of course, be milli-
metres, but there is no necessity for the wire to be of any definite length ;
all that is required is that it should be accurately divided, the measure-
ments to be taken from it being not absolute, but comparative. German-
silver wire is usually employed because its conductivity is but little
affected by variations in temperature. An ebonite block, provided with
a metal pin, is made to slide along the board and is connected with a
wire, the other end of which may be attached to one pole of the battery
or to a galvanometer. The metal pin is usually provided with a spring,
so that it may be pressed down upon the wire or not, at pleasure, thus
forming a ready means of making or breaking the circuit. To the middle
of the strip of copper, A, a binding-screw is attached, and to this is fast-
ened one of the battery wires. Binding-screws are also attached to the
two ends of A, and to the adjacent ends of the side-strips B and D. In
these binding-screws strips of wire, r' and n3, can be placed so as to fill
up the breaks between the side-strips and the ends of the longitudinal
strip. A, B, and D are connected with a delicate astatic galvanometer,
G. This being the construction of the Wheatstone bridge, its mode of
action will be, perhaps, better understood by the following diagrams and
demonstrations:—
GALVANISM.
A-217
It was found necessary, in experimenting with thousands of miles of
cable or insulated wires, to adopt some standard point, in order to ascer-
tain exactly the resistance of the whole. The matter was put into the
hands of a committee of the British Association, who determined that
an English mile of pure copper wire, No. 16, should be the B. A. unit;
they further constructed a wire of silver and platinum, because it was
little affected by temperature, which they deposited as the standard of
comparison, and this length of wire they estimated in figures to be 13.59
of the length of the copper wire. Bobbins upon which hundreds and
thousands of miles of copper wire, No. 16, would have to be wound
would be too bulky and cumbersome to manage ; it has, therefore, been
arranged that German silver, an alloy of about 60 parts of copper with a
fraction of lead, 25 of zinc, and 15 of nickel, should be employed, because
it has about thirteen times less
conducting power than the
same-sized copper wire; con-
sequently the standard unit
would be represented as fol-
lows : B. A. unit of German-
silver wire equals 13.59 of an
English mile. The bobbins
having 13.59 of an English mile
of German-silver wire wound
upon them represent, there-
fore, a resistance equal to one
mile. The following physical fig. 12.—wheatstone bridge.
law is the outcome : The re-
sistance of a conductor of any given metal is directly proportional to
its length, and inversely proportional to its thickness, or cross-section.
In order to demonstrate clearly the practical value of the Wheat-
stone bridge, inasmuch as it is so often difficult to thoroughly com-
prehend its construction and the principles underlying it, I append the
following diagrams, with a brief demonstration1 :—
For the sake of simplicity the brass bands and brakes only are
shown. The galvanometer is supposed to be resting in the middle of the
board, the battery on the right, and the connecting-key on the left.
For the sake of discussion, it is supposed that the current coming
from the battery, Ba, is represented by twelve parts ; these, on arriving
at P, split or divide into equal parts ; six go in the direction, A', and
six in the other, A.
The two currents represented by arrows both pass through equal
1 These diagrams are made from the Wheatstone bridge used for demonstrating a broken
cable at the Polytechnic of London by Mr. Becker. The bridge is constructed eight feet long
and two feet eight inches wide; the lozenge-shaped brass plates are one and one-half inches
wide. There are four brakes with binding-screws, and, by using bobbins upon which the B. A.
unit of German-silver wire was wound, the students were made to understand that each bobbin
represented a mile of pure copper wire, No. 16.
A-218
BLETER.
resistance coils, A', A, and tjie respective currents might pass direct to
the key, K (where contact is made or broken), and through that to the
other pole of the battery ; but the currents are partially arrested by the
equal resistance coils, B', B, and a portion of the currents is forced into
or divided into the galvanometer, G N.
The use of the coils, or any other resisting matter, on the other side
of the galvanometer is to force, or rather gently to impel, a part of the
current into the galvanometer; because if this were not done the deflec-
tion would be so small that it might be barely perceptible.
Let us say, for the sake of discussion, that 2 parts pass to the
galvanometer from Q and 2 parts from S; such currents, coming in
opposite directions, must oppose each other's progress through the gal-
vanometer, and therefore the needle of the latter does not move.
We have only now to suppose that 4 + 2 = 6 proceed from Q to
Fig. 13.
R, and 4 -(- 2 = 6 by S to R; the two added together make 12, the
original quantity started with, which proceeds through the key and con-
necting wire to the other pole of the battery, Ba.
The second diagram consists of two parts, viz., Part I and Part II,
and it is recommended that the latter be traced on tracing-paper and
placed upon the former. The current again is represented by 12 parts.
The resistance of the coil at A'', Part I, being less than A, Part II, the
greater part of the current—say, 8 Af parts—goes through the former, and
4 A through the latter, consisting of a piece of copper wire and a resist-
ance coil; therefore, returning to Part I, the current going by A1 through
QtoGN, the galvanometer needle, forms, at the point Q, a greater partial
current (say, 3 parts) than the current going by A, Part II, which divides
at S, and is represented by, say, 1^ parts ; therefore, the current that de-
flects the galvanometer is the greater going by Q, Part I, and marked 3;
GALVANISM.
A-219
consequently, it amounts in imagination to a struggle between the cur-
rent going by Q, Part I, represented by 3 parts, and the current going
by S, Part II, or 1^ parts. The issue cannot be doubtful; the greater
Fig. 14.
current, 3, overcomes the lesser, 1^. In Part I, 4 -f- 3 = 7 go by B, and
in Part II 5 go by B'; and if the two are added together they again make
the 12 parts, which, as before, travel through the key and connecting wire
to the other pole of the battery, Ba.
S
Fig. 15.
The next diagram (Fig. 16) explains the use of the bridge for com-
paring the conductivity or resistance of wires of different metals or
different lengths of same wire. The lower part (A to B) of the bridge
marked in dotted lines is not required, its place being filled by a long
German-silver wire stretched from P to R, and provided with a scale
A-220
BLEYER.
divided, say, into 20 parts; on this the galvanometer screws, the other
screw of the galvanometer being connected with Q.
In this case we are to suppose it is being used to ascertain the
relative lengths of wire of the same metal, diameter, and conductivity.
The clip, S, has been moved from the centre, C, to No. 13.334 on the
scale painted below the wire, P to R. The clip has been moved to 13 334,
or until the galvanometer is at rest; this quantity, 13.334, is double that
of R to S, therefore the resistance at B' is shown to be half the resistance
at A', because A' has two coils or two miles of wire, and B' one mile; so
that it is shown, without any previous knowledge of the absolute length
of the two coils at A' (the wire under examination)., that it is double the
length of the known quantity, one mile at B', because the scale from R
Fig. 16.
to 8 is 6.666, and that from P to 8 13.334, and if one is added to the
other they make up the whole scale of 20.
THE GALVANOMETER.
It is of the highest importance that the electro-therapist shall be
able, during the course of an electrical seance, to see at a glance in what
direction the currents are passing, and measure their strength. For this
purpose a galvanometer of some form or make is necessary.
One of its most important functions is the testing and measurement
of the resistance of line wires, instruments, coils, batteries, and insulation,
and for many other similar purposes.
Its operation depends upon the action of the two forces—electricity
and magnetism—and, though galvanometers are made in many forms
and are used in several different ways, they are all based on the funda-
mental fact that a magnetic needle is deflected or turned aside from its
GALVANISM.
A-221
natural position by the passage of a current of electricity in a conductor
placed parallel to it.
When a steel needle is magnetized and delicately pivoted at its
centre, so that it is free to move horizontally, every one knows that it
will set itself north and south, a common example being the ordinary
compass-needle.
This action of the needle is due to the influence of the earth, which
is itself an enormously large and strong magnet. All magnets attract
the opposite poles and repel the similar poles of other magnets. For
instance, the north pole of the earth attracts the south pole of the
magnetic needle, causing the needle to point north and south as it
does.
Among those who had studied most deeply the phenomena of gal-
vanic electricity was Hans Christian Oersted,—a Danish physicist and
professor of physics in the University of Copenhagen,—of whom we
have already spoken in our " historical sketch." Oersted's researches led
him to suspect the identity of magnetism with electricity, but for a
long time no means of experimentally proving the fact revealed itself.
The expedient had been tried, but without results, of placing the two
poles of a battery, as highly charged as possible, in a parallel line with
the poles of a magnetic needle. In one of the reports of the Smithsonian
Institute the story of his discovery is thus graphically told : " Fortune,
it might be said, ceased to be blind at the moment when to Oersted was
allotted the privilege of first divining that it was not electricity in
repose accumulated at the two poles of a charged battery, but electricity
in movement along the conductors by which one of the poles is discharged
into the other, which would exert an action on the magnetic needle.
While thinking of this—it was during the animation of a lecture before
the assembled pupils—Oersted announced to them what he was about to
try. He took a magnetic needle, placed it near the electric battery,
waited till the needle had arrived at a state of rest; then, seizing the
conjunctive wire traversed by the current of the battery, he placed it
above the magnetic needle, carefully avoiding any manner of collision.
The needle was at once in motion. The question was solved. Oersted
had crowned, by a great discovery, the labors of his whole precious
life."
On July 21, 1820, the discovery was announced that a galvanic cur-
rent passing through a wire placed horizontally above and parallel to an
ordinary compass-needle, would cause that needle to sway on its axis to
the east or west, according to the direction of the current through the
wire. Oersted's discoverv may be said to have pointed the way to the
great applications of electricity to human use, for it showed that energy
in the form of electricity could be converted into energy in the form of
mechanical motion.
What are the Underlying Principles of the Galvanometer?—The
A-222
BLEYER.
amount of deflection of a magnetic needle depends, to a certain extent,
upon the strength of the cureent.1
" If the electric wire is above the needle, and the direction of the
current is from north to south, the needle will tend to point eastwardly.
Leaving the wire still above the needle, and changing the direction of
the current so that now it flows from south to north, we find that the
north end of the needle now deflects in a western direction. If the wire
is changed to a position under the needle, it is found that all the motions
are reversed ; for passing a current from south to north the needle has
an eastward inclination.
" It should be here explained that when we speak of the deflection of
a needle the north end of the needle is uniformly the one referred to,
the south end, of course, moving in an opposite direction.
" It can be readily understood why these movements should occur, and
their reason. We have already indicated the cause of the natural inclina-
tion of the magnetized needle to place itself in a position pointing north
and south to be the attraction of a much stronger magnet—the earth—
and we may easily believe that an unseen force which causes the needle
to point away from the north must also be of a magnetic character ; and
so it proves to be, and the reason of the deflection is as follows :—
" A wire carrying electricity becomes practically itself a magnet; that
is, a straight current produces in a wire a magnetic field. This any one
may easily prove for himself by passing an electric current through a
wire of iron, copper, brass, or any other metal, and permitting the wire
to dip into a heap of iron-filings. The filings will instantly cling to the
wire and all around it, just as if it were a natural magnet. The electric
wire having thus virtually been transformed into a magnet, when placed
beside the magnetic needle, interferes with the attraction of the earth
and pulls the magnetic needle to one side.
" The case is simply a very weak but very near magnet—i.e., the cur-
rent-carrying wire acting on a poised magnetic needle—in opposition to a
very strong but very distant magnetic pole, the north pole of the earth;
and thus the needle, being acted upon by both oppositely, takes up a
half-way position,—as it were, 'on the fence.'
" The earth's magnetism tends to make the needle point north and
south; the electric current acting on the needle tends to make it assume
a position pointing east and west. The resultant force will, of course,
be between the two, and will depend on their relative strength. If the
current is very strong the needle will turn a long way around, but never
farther than to a complete right angle."
Up to this point the effect of one parallel wire only had been con-
sidered. But if a greater deflection be required, and the battery power
cannot conveniently be increased, what is to be done?
If the battery power cannot be increased in this manner, we can
1 Electrical Measurements and the Galvanometer, T. D. Lockwood, 1890
GALVANISM.
A-223
increase its power of acting upon the needle by using a parallel wire on
both sides of the needle ; for, if the conducting wire is carried first over
the needle from north to south and then back from south to north under
the needle, the effect will be doubled. If the wire, instead of making only
one such convolution round the needle, were to make two, the force
would again be doubled; and if several combinations are wound around
the needle, the force would be increased nearly in proportion to the
number of convolutions.
If the convolutions are greatly multiplied so as to form a coil, the
force is enormously increased, and we have what the first constructor of
the galvanometer called a " multiplier." All gal-
vanometers, therefore, consist of a coil of insulated
wire and a magnetic needle delicately suspended in
• such a position as to be easily deflected by the
passage of a current of electricity through the coil.
These, with the addition of a dial-plate, graduated
so that the movements of the needle may be
interpreted, are the only absolute essential features of the instru-
ment.
The galvanometer was one of the earliest results of Oersted's dis-
covery; it was, indeed, in the same year (1820) that the first galva-
nometer was invented by Prof. Johann S. C. Schweiger, of Halle. He
gave it the name of " multiplicator," the object of which, as aforesaid,
was to multiply the electro-magnetic action of the current. This instru-
ment is actually so sensitive that it serves
to detect the weakest electric currents.
All parts of the current traversing the
elongated parallelogram, p q r o n (Fig.
It), in the direction of the arrows, act
in a similar manner upon the needle, a b,
which rotates in a horizontal plane. If
a be the south end and 6 the north end,
the current will show a tendency at- all
points to turn the needle in such a manner
Fig. 18.—Schweiger's L
Multiplier. that b shall project beyond the plan of
the figure, while a will retreat behind it.
The lower portion of the wire, therefore, supports the action of the upper
in the same manner as does the current of the same force, moving in the
same direction around the needle in the portions p q and r o. A second
current of the same force, moving in the same direction around the needle,
will produce as great an effect as the first; so it will be with a third, a
fourth, etc. A wire, therefore, wound around a needle in one-hundred
convolutions, all of which are traversed by the same current, must pro-
duce an action of one hundred times greater intensity than one of a
single convolution ; the current must not, however, be propagated later-
A-224
BLEYER.
ally from one winding to the other, but must traverse the wire through-
out its whole length, being carried actually around the needle.
The Schweiger multiplier is represented on preceding page. The
difference between the rectangular and circular form is merely a matter of
detail. Although the ordinary galvanometer, con-
structed as stated, is very well adapted to detect
the presence or to indicate the direction of a cur-
rent for some simple measurements, especially for
those in which the deflection is not greater than
fifteen or twenty degrees, it is not to be depended
upon for any testing in which a greater deflection
is produced, for the following reason, that when
Fig. 19. a needle is deflected it is not in the same position
in its coil as when at zero; the greater the deflec-'
tion, the farther is the needle removed from the position where its coil
most powerfully influences it, and the nearer the needle approaches the
right angle, at which point the coil has no influence on it at all, the weaker
does the action of the current become.
Fig. 20.—Tangent Galvanometer.
In order to overcome this difficulty, and for other mathematical
reasons, galvanometers have been invented in which the tangent, or line
of the angle of deflection, is proportional to the strength of current
measured. These are called tangent, or sine, galvanometers.
The Tangent Galvanometer.—The tangent galvanometer consists,
broadly speaking, of a ring having a groove on its edge filled with in-
GALVANISM. A-225
sulated wire, and provided with a needle, which must not be longer than
one-sixth of the diameter of the ring, hung or pivoted precisely in its
centre, as shown in Fig 19.
This instrument, as shown in Fig. 20, is mounted on a hard-rubber
base, seven and three-eighths inches in diameter, provided with leveling
screws and anchoring points. The galvanometer consists of a magne-
tized needle seven-eighths of an inch in length, suspended at the centre
of a rubber ring, six inches in diameter, containing the coils. The
coils are five in number, of the resistances 0, 1, 10, 50, and 150 ohms.
The first is a stout copper band of inappreciable resistance ; the others
are of different-sized copper wires, carefully insulated. Five terminals
are provided, the plug holes of which are marked, respectively, 0, 1, 10,
A/ 73 /o___.s B ______ -P
F
E
Fig. 21.
50, and 150. The ends of the coils are so arranged that the plug inserted
at the terminal marked 150 puts in circuit all the coils at the terminal
marked 50, except the 150-ohm coil; and so on, till at the zero ter-
minal only the copper band is in circuit.
Fixed to the needle, which is balanced on jewel and point, is an
aluminium pointer at right angles, extending across a five-inch dial imme-
diately beneath. On one side the dial is divided into degrees; on the
other it is graduated, the figures of the scale corresponding to the
tangent of the angles of deflection.
For the benefit of the non-mathematical experimenter we may
explain that a tangent is a line drawn at right angles to one of the
diameters of any circle and touching the circumference, as in Fig. 21.
A to D is a tangent to the circle B, C, E, and F.
15
A-226
BLEYER.
In the case of the tangent galvanometer the dial of the instrument
is the given circle, and the zero point is the point at which the tangent
touches the circle. The tangent is therefore an imaginary line, which
must be parallel to that diameter which connects the degree of 90 on
one side to the same degree on the other side, and at right angles to the
diameter or line connecting the two zero points. Let us suppose that
the circle is the dial of a galvanometer marked off into degrees, and that
the needle, by a given current, is deflected to 27 degrees; double the
Fig. 22.—Sine Galvanometer. the same galvanometer. If a
tangent galvanometer is gradu-
ated to degrees only when it is used to obtain correct results, we must
reduce the degrees to tangents by means of a table of tangents.
A tangent and sine table can be found in many of the first-class
works,—as in Lockwood's " Electric Measurement."
The Sine Galvanometer.—The sine galvanometer, which was invented
by Pauillet, is one in which the coils are made movable, so as to be
capable of revolving on the axis around which the needle turns. The
needle is pivoted, or suspended horizontally. A scale graduated with
degrees is attached to the coils, and a pointer fixed in the base so that the
angle through which the coils are turned can be observed.
When the needle is deflected by a current passing through the coils
the coils are turned by hand, following the needle in its deflection ; as
the coils are thus turned they, of course, maintain their power on the
needle, and it accordingly diverges still more, but the angle it makes
GALVANISM.
A-227
with the coils becomes less and less, until at length a point is attained at
which the needle remains parallel with the coils. When this point is
reached, the influence of the earth's magnetism exactly balances the
deflective force of the current. The strength of the current that pro-
duces the deflection will then be directly proportional to the sine angle
through which the coils are turned. It is customary, as in the use of the
tangent galvanometer, to read off the degree, and refer to a table of sines
for the required sine.
The sine galvanometer is not so convenient for general use as the
tangent galvanometer is, being most applicable to scientific experiments
and for measuring and comparing weak currents.
The astatic galvanometer is one of the most sensitive instruments
employed; so is the Thompson
mirror galvanometer.
The differential galvanometer is
one which has a needle poised or
suspended like that of the tangent
or sine galvanometers, but, unlike
them, the needle is acted upon by
two coils of equal length and resist-
ance, insulated from one another
with great care. These coils each
surround the needle with an equal
number of convolutions, which, in
each wire, are equidistant from it.
When this galvanometer is used,
one end of each coil with a wire
leading to the pole of the battery is
attached in such a way that the cur-
rent flows in opposite directions through the two wires. Now, if the
current in both coils is of the same strength, one tends to deflect the
needle to the right and the other to the left, and the needle, being pulled
with equal force in both directions, remains at rest. If, however, one
current be made stronger than the other, the balance will be destroyed
and the needle can be moved by the stronger current.
Unknown resistance can be measured with this galvanometer. This
can be done in the following manner: We insert the resistance to be
measured in the circuit of one of the coils. This, of course, weakens the
current in that coil, and consequently its effect on the needle, which no
longer remains balanced, but deflects to one side. If we now insert a
rheostat in the other side and unplug the resistance until the needle again
balances or comes to zero, we know that the current in each coil must
again be equal, and, therefore, that the unknown resistance in the circuit
of one coil must be exactly equal to the resistance unplugged from the
rheostat.
Fig. 23.—Astatic Galvanometer.
A-228
BLEYER.
A Dead-Beat Galvanometer.—So called on account of the readiness
with which this galvanometer needle comes to rest, instead of swinging
repeatedly to and fro.
There exists, besides these galvanometers for the commercial meas-
urements of currents, a variety of forms. They are generally so con-
structed as to read off the amperes, volts, ohms, watts, etc., directly.
They are called amperemeters, wattmeters, etc. For their fuller descrip-
tion reference should be had to standard works on electrical measure-
ments.
Having so far spoken of the cursory account of the theory of the
galvanometer, and having described several of them, I will turn your
attention to several galvanometers which possess certain features that,
from the nature of the work they are called upon to do, are common to
all galvanometers for medical purposes. We find the most important
point connected therewith is, perhaps, the method of graduation. They
are invariably of the fixed-coil, or " tangent"' type,—that is to say, accord-
ing to Steavenson and Jones (" Medical Electricity "), " the current indi-
cated by any reading is proportional not to the angle of deflection, but
to the trigonometrical tangent of that angle. Hence, it is necessary that
the circle on which the position of the needle of the galvanometer is read
must be graduated not uniformly, but so that the readings are angles
whose tangents increase uniformly."
Calibration of a galvanometer is often called the graduation of a
galvanometer. The galvanometer is graduated by dividing its circle into
360 degrees before the process begins.
The calibration of a galvanometer, for example, consists in the
determination of the law which governs its different deflections and by
which is obtained in amperes either the absolute or the relative currents
required to produce such deflections. For various methods of cali-
bration, see standard works on electrical testing, etc.
When a galvanometer is calibrated to read in milliamperes it is
called a " milliamperemeter," just as one calibrated to read in amperes is
called an ammeter. The milliamperemeter is chosen as the standard for
use in electro-therapeutics.
Many galvanometers are provided with a set of two or three resist-
ance coils, which may be inserted in parallel with the galvanometer coils ;
they are usually of such values that they only allow one-tenth or one-
hundredth or one-thousandth of the whole current to pass through the
galvanometer.
The sensibility of a galvanometer may be varied in a very simple
manner by the use of such coil, which is termed a shunt.1 A shunt is a
resistance coil, or coil of fine wire used to direct some definite portion
of a current, taking it past a galvanometer instead of through its coils.
1 Electricity and Magnetism. Fleeming Jenkin, F.R.S.S., L. and E., London. For the
mathematical part relating to shunts, see works on physics.
GALVANISM. A-229
Thus, let G, Fig. 24, represent the shunt. Let the resistance of the
shunt be one-ninth that of the galvanometer, then of a total current
from C to D nine parts go through the shunt and do not deflect the
needle, while one part goes through the galvanometer; only one-tenth
of the whole current is, therefore, effective in deflecting the needle, and
the deflection, supposing a mirror galvanometer be used, is only one-tenth
of what it would have been had no shunt been used. Similarly, by making
the shunt equal in resistance to one-ninety-ninth of the galvanometric
Fig. 24.
coil, we reduce the sensibility of the instrument to the one-one-hundredth
part of its original sensibility.
All instruments used by electro-therapists are invariably cali-
brated and marked, as aforesaid, to read in milliamperes, by all their
manufacturers. These milliamperemeters are made up into two different
styles, as the vertical and horizontal. Fig. 25 is a horizontal one
designed for physicians; it is direct reading, and thus a means of
obtaining quick, accurate, and reliable electrical measurements, such as
A-230 BLEYER.
have hitherto been unattainable. No time is required for adjusting or
waiting for the needle to come to rest, but readings can be taken imme-
diately as soon as the circuit is closed. This instrument is accurately
Fig. 25.—Horizontal Mil-am-meter.
calibrated and standardized. The staff is of hardened steel pivoted in
ruby bearings with jeweled end-pieces ; it is provided with a switch, which,
when placed on the 50 button, selects the lower or red scale on dial read-
Fig. 26.—Vertical Milliamperemeter.
ing from 0 to 50 milliamperes, and when placed on 500 reads black or top
scale, 0 to 500. It is mounted in a well-made mahogany or antique-oak
case. For more delicate measurement this milliamperemeter is divided
GALVANISM.
A-231
on a lower scale, from 0 to 10 milliamperes, and again subdivided in
such a manner that one-tenth of a milliampere can readily be read off.
Among the vertical milliamperemeters the one made by Waite &
Bartlett is the best, for many reasons.
The coils are made of two semicircles, so that practically you have
a horseshoe solenoid for affecting the needle. The resistance of these
coils combined averages fifteen-hundredths of an ohm. The magnet is
made in horseshoe form, the poles of which swing in a circular groove
in a copper block ; the effect of this is to dampen the magnet, and so
make it dead-beat. The magnet is supported on a jewel-point, which is
so arranged that it can be lifted from the needle-point while being trans-
ported, which prevents injury to point of needle and jewel. All of the
milliamperemeters made by the Waite & Bartlett Manufacturing Com-
pany are calibrated individually, and, for this reason, are uniform and
Fig. 27.—Mil-am-meter.
correct. The instruments are in an all-brass case, finished in the same
style as a microscope.
Another very excellent vertical mil-am meter is the one manu-
factured by the Chloride-of-Silver Dry-Cell Battery Company, of Balti-
more. These meters have qualities which must also prove themselves
satisfactory to the therapist. The following claims are made for them :—
1. An absolute electrical meter should be accurate. The best con-
ditions for this accuracy are the use of short magnetic needles in
connection with a long pointer. In this meter the magnetic needles are
less than one inch long, while the pointer—made of aluminium for light-
ness—is four inches long, thus securing an extended indication on the
scale for a very slight movement of the needles.
2. Such a meter should be as free as possible from variations due to
changes of time and surroundings. This double object is accomplished
A-232
BLEYER.
by employing a horizontal movement and an astatic system of magnetic
needles, controlled by a fixed magnet, which is permanently under the
influence of an armature or keeper, for preserving a uniform degree of
magnetism. Such a system of needles is free from the influence of the
earth's magnetism, and is the most constant in its action.
3. Friction must be entirely absent. This is accomplished by the
use of a perfectly-pointed steel pivot working in a concave jewel, as in
the best absolute galvanometers known to electricity.
4. The free parts of the instrument must be provided against acci-
dental displacement. This is attained by a simple detail of mechanism,
so that the magnetic needles cannot get off the pivot, even if shaken
wrong-side-up or otherwise roughly used. A simple-locking device also
provides for lifting the needles from the pivot and holding them fixed
for transportation.
5. A physician's milliamperemeter should be readable from either a
sitting or standing position. In this meter the face is at the front,
at an angle which satisfactorily meets these points.
6. The perfect meter should have a wide range of measurement.
This has been obtained in this meter by an entirely new arrangement.
Three independent reading-scales are stamped at equal distances apart
on the three faces of a celluloid roller. One of these scales is marked in
5 milliamperes, divided into halves. The second scale is divided into 25
milliamperes, and the third scale reads up to 250 milliamperes. This
meter reads directly.
Besides these described there are others, as the Weston standard
direct-reading mil-am-meter, which has a scale of 0 to 500, 0 to 10. The
instrument is readable from 0 to 10 milliamperes by one-tenth ; 0 to 500
by 5 milliamperes. This instrument will operate in any position, and is
not influenced by magnetism.
The Mcintosh milliamperemeter has many advocates, and is certainly
a very fine and accurate instrument. The D'Arsonval and the Gaiffe are
also well known, besides many other American and foreign makes.
The Galvanometer Battery Gauge.—This is a new instrument en-
tirely, and differs essentially in its construction and aim from all other
galvanometers. This gauge is constructed and calibrated to furnish a
reliable standard for the practical measurements of current-strength of
from 1 to 5 cells of ordinary batteries. A good Leclanche cell will indi-
cate about 9 degrees; Burnley dry battery, 14 degrees; Lockwood
American District (blue vitriol), 6 degrees ; Crowfoot Western Union
form, 8 degrees.
These gauges, being calibrated to a single standard, furnish an
accurate instrument for battery comparisons or condition tests. The
gauge being a true galvanometer, without springs or magnetic devices,
its indication for a given force is always the same. It can be used
standing upright on table or desk, or suspended by its chain and ring,
GALVANISM.
A-233
which brings the needle to zero when no current is passing the instru-
ment. Also, on account of their normal positions being upright, these
gauges can be advantageously used as permanent circuit-indicators.
The action of the needle is " dead-beat." It moves to and remains,
without oscillation, at whatever indication the current calls for.
Two silk-covered conducting cords are attached to each gauge.
These cords are provided with new and improved tips, made so as to
enter any binding-post, and to be held by the binding-screw in the usual
way, or, being square, can be firmly held by the English form of binding-
post. These tips have a spring-clamp, by which they can firmly grip
Fig. 28.—The Galvanometer Battery Pocket-Gattge.
naked wire (up to No. 16) at any exposed point, and thus also be able
to detect a flow in circuits of fire-alarms, burglar-alarms, etc. Such a
gauge must become serviceable to medical men to detect the power of
their batteries, which is highly essential during or before treatment of
any case.
RHEOSTATS.
The name rheostat was originally given by Wheatstone to an instru-
ment which he devised for the purpose of varying at will the amount of
resistance in a circuit.
The modern rheostat is a box containing a number of spools filled
A-234
BLEYER.
with insulated wire ; the resistance of the wire on each spool being equal
to some multiple or submultiple of the ohm, the unit of resistance. The
several coils (Fig. 29) and a complete box-rheostat (Fig. 30) are shown
below.
The different coils may be of any required resistance, and may be
Fig. 29.—Coils.
varied indefinitely. They are usually made to increase consecutively,
as, for example, 1, 2, 5, 10, 20, 50, 100, 500 ohms, and so on.
If all the plugs are in their places, there is practically no resistance
between the terminal binding-screws ; but if any of the plugs be taken
out, the coil of that section is brought into the circuit. It follows, then,
that by withdrawing any or all of the plugs we can introduce less or
more resistance.
Numbers representing the various resistances of the coils are usually
Fig. 30.—Standard Dox-Rheostat.
placed opposite the holes, and by adding together the numbers unplugged
we ascertain the total resistance inserted.
The wire used in resistance coils is generally made of German silver,
because the resistance of that alloy changes very little with variations of
temperature; it is insulated with silk, and always wound double, as
GALVANISM.
A-235
shown, so as to neutralize any inductive action of the convolutions on
each other, and also to prevent the coils from affecting galvanometers
near them ; when so arranged, the current flows at the same time in two
opposite directions round the spool, effectually preventing any inductive
troubles.
It is usual to so arrange the different resistances that, by properly
combining them, any value, from a fraction of an ohm to 10,000 ohms,
can be obtained.
Those rheostats which are now mostly used by medical men are of
the wire, the water, and the carbon order. I will describe and illustrate
the three different kinds. They all have their merit and their demerit.
The Vetter Carbon Rheostat.—The principle adopted in the con-
struction of this rheostat is the effect of variation in resistance, which
Fig. 31.
takes place in carbon with a change in pressure. A quantity of specially-
prepared carbon, in a finely-divided state, is placed in a small rubber
pouch or cylinder, which is inclosed by two metal plates, to which the
two sides of the circuit are connected. The lower plate is fixed to the
base of the instrument, and the other, traveling in upright guides, can be
depressed, by means of a screw with a fine thread, so as to compress the
carbon in the rubber cylinder. In this way the current passing can be
adjusted with the greatest nicety. The variation in the resistance of the
rheostat follows the movements of the screw through very wide limits,
thus controlling from off or no current to the full capacity of the battery.
This instrument is far in advance of any rheostat, switch-board, or
cell-selector. It imposes equal work upon all the cells of a battery,
maintaining the current throughout the series of uniform and equal
strength. There is also a saving of a mass of complicated wires from
the cells, as only the two terminal wires from the battery are necessary.
A-236
BLEYER.
The absence of liquid in glass and the many advantageous features
it possesses make it the most desirable instrument for the purpose.. •
The Water Rheostat.—This is another resistance apparatus much
lauded over by some medical men. There are several of them in the
market. The latest of them is the Bailey current-controller.
This instrument, briefly described, consists of two triangular-shaped
carbon plates, each carrying a conical sponge at one of its angles, and
mounted over a glass vessel containing water. By means of a worm gear
operated by a thumb-knob the sponge-tips are gradually immersed into
the water and toward each other. It is so arranged that by turning a
thumb-screw the left-hand plate may be unlocked from the gear and im-
mersed as far into the water as desired, and then the other plate gradu-
ally moved toward it. This, the last method, gives a more gradual in-
crease of current, as one plate is moved in place of the two. Each plate
Fig. 32.—Bailey Current-Controller.
measures three and one-half inches by three and one-half inches by four
inches ; the entire device is over all seven inches long, seven inches wide,
four and one-half inches high, and weighs two pounds. This current-
controller, or rheostat, will give a current at the outset more feeble than
any other instrument of this kind or character, and will increase the cur-
rent without variation or fluctuation. When the plates are raised out
of the water they are separated fully three-sixteenths of an inch ; thus it
is impossible for the escape of the current by means of water adhering
between the plates, or by moisture or condensation.
The principal advantages of the water rheostat over the wire-coil
rheostat, are as follow : Its simplicity, avoiding the complicated wiring-
incidental to wire rheostats; greatest certainty of preventing shocks,
and its low value.
The ordinary water rheostat is known to most practitioners. It
consists of a glass cylinder, water-tight, and filled with water or some
GALVANISM.
A-237
saline solution. It terminates below in a metal foot and binding-screw,
and a metallic rod, moving stiffly, passes in from above through a collar,
and this carries the other binding-screw. When the rod is pushed quite
down it touches the base of the tube, and the circuit is completed through
the metallic contact; when it is raised the current must pass through
the badly-conducting fluid.
A good rheostat is the Mcintosh hydro-platinum. The figured one
in the cut is devised for the special object of rendering it possible
of increasing or decreasing the strength of the current in absolute gradual
gradations, from zero to the full current-strength
and back again.
Between two small, thin sheets of platinum
(D D) suspended in water with suitable attach-
ments (A A) for one pole of the battery is sus-
pended a third piece of platinum (E) with pointed
end, which can be lowered or elevated gradually in
the water between the other two sheets (D D), by
means of a delicate ratchet combination (B C)
above. This plate is connected with the other
pole of the battery by one of the binding-posts
(A). When plate E is elevated so that its pointed
lower end is out of the water no current can pass
the instrument, but as it is gradually lowered
into the water the resistance becomes gradually
less and less, until the desired current-strength
is reached, or until the full capacity of the battery
is obtained. Thus, by elevating or lowering this
central sheet, a current of great strength can be perfectly controlled in
gradual gradations, no shock being possible.
There are other kinds of rheostats made by the various surgical-
instrument makers throughout most of our large cities. Those made by
the Waite & Bartlett Manufacturig Company are perhaps the most widely
known.1 The Massey current-controller is a modification of the one
known as the old Butler rheostat.' The above-named firm have under-
taken its modification, and to-day it looks as follows : The disc is made
of slate with the cone-shaped surface roughened for retaining the graphite
coating. The advantage of the slate is that it does not become soiled
like the mart's, and it always presents a neat appearance. The brush
for moving over the resistance surface is made of spring-brass nickel
plated, sufficiently broad to span the broadest part of the leaden
portion, and the spring is split up in several places to insure perfect
contact over the entire surface upon which it rests. One of the binding-
posts attached to the wooden frame surrounding the disc connects with
1 Augustin H. Goelet, M.D.
136,137.
The Electro-Therapeutics of Gynaecology, vol. i, pp. 135,
A-238
BLEYER.
the base of the leaded surface by means of the spring contact under
the cap, and the other with the central pivot, to which the brush is
attached by a lever; so that there is a break, so to speak, between the
two when the brush stands at the point marked " start," removed from
the coated surface. As the brush is moved upon the graphite the resist-
ance is diminished the nearer it approaches the base. The graphite,
which is really a good conductor of the current when spread out over a
flat surface like this, offers a considerable resistance. In order to in-
crease the resistance at the start, so as to permit the current to be turned
on gradually from a battery of a great number of cells, it is necessary to
make the graphite coating very much thinner there than elsewhere, and
if too much has been put on it should be rubbed off until its presence is
Fig. 34.—The Massey Current-Controller.
scarcely perceptible at and near the starting-point. The only objection-
able feature about the instrument is the perishable character of the
graphite coating, which is being constantly rubbed off by the brush, but
it is easily renewed by rubbing over the surface a carpenter's lead-pencil,
or, in fact, an ordinary pencil; but the former having a larger surface of
lead, the coating can be renewed more rapidly. It is possible with this
rheostat to gradually remove the entire resistance by moving the brush
up over the surface which has been covered with graph'te, or, at least,
the remaining resistance is so little as to be inappreciable.
The advantages of this rheostat are that it is flat, it occupies a very
little space, it cannot be upset, and the connections are practically inde-
structible. It can be readily removed from the cabinet or table and
transported for use elsewhere, though its size (the diameter being about
seven or eight inches) makes it rather an awkward instrument for carry'
ing conveniently in a bag.
GALVANISM.
A-239
Dr. A. H. Goelet, recognizing the fact that a smaller rheostat was
needed for use with a portable battery at a patient's house,—one small
enough to make a convenient package and readily carried in the pocket
Fig. 35.—Goblet's Slate Pocket-Rheostat for Galvanic Current.
from place to place,—was led to suggest the modification of this rheostat
shown in the cut (Fig. 35), which is made for him by the Waite &
Bartlett Manufacturing Company. It is a small disc of slate, only
three inches in diameter, marbleized on the upper face and around the
Fig. 36.—Willms's Rheostat.
side. Around the margin of the upper face is a raised surface about
one-quarter of an inch wide, not marbleized, but roughened for receiv-
ing a coating of graphite. The connections are made in the same
A-240
BLEYER.
manner as in the Massey instrument. The contact of the lever with
the graphite surface is made by a small wheel ground to fit the raised
surface, which is made level, and in front of the wheel is placed a pro-
jecting spring-pressure foot, like that on a sewing-machine, to which is
attached a piece of graphite for constantly renewing the coating. The
object of the wheel is to make it move more smoothly and to avoid sud-
den jerks. The lever is turned by a thumb-screw fixed to the pivot
passing through the centre of the disc, and can be manipulated with
greater ease than the other instrument. It can be used with forty or
fifty cells as satisfactorily as the other instrument, but the same care
must be observed not to have the graphite coating too heavy at the
starting-point. Nearly all the resistance is cut out at the finish. A
larger size is made, but it is not so convenient.
Fig. 36 represents a rheostat, recently introduced by the Chloride-
of-Silver Dry-Cell Battery Company, of Baltimore, designed by Mr.
Charles Willms, of the firm. The resisting material, consisting of com-
mon glue, graphite, and metal-filings (brass preferred), is placed on the
under surface of the top plate; the graphite being really the resisting
material, the brass-filings collecting the current and conducting it to the
metal contact-points leading to the surface, where the turning-crank
forms a connection with them. This is considered a very finely-
constructed and practical instrument. Most of the portable batteries
have been so designed that a rheostat is placed on the mechanism in
such a way that is most practical.
Introductory Remarks on Primary Batteries.
Battery Defined.—An electric battery, or cell, as a single element is
called, is a device for the conversion of the potential energy of chemical
separation into the energy of an electric current. Thus, the metal (zinc)
and the sulphuric acid which acts chemically on it represent energy of
chemical separation in the potential form. If now the zinc is placed
alone in the acid, this energy of chemical separation is converted simply
into heat, when the zinc displaces the hydrogen of the acid with the
formation of zinc sulphate ; but if the displacement of hydrogen by zinc
is made to take place under certain less-simple conditions, then a part at
least of the kinetic energy developed takes the form of the energy of an
electric current. The arrangement of parts necessary to secure these
conditions, which determine that the transformed energy shall be elec-
trical, is called a battery, or voltaic cell.
The term " battery " is now to be found substituted in all works on
electro-physics for the former historical one," pile." It is stated by many
that the word " pile " is, however, more correct.
The invention of the "electric pile," or battery, was Yolta's great
contribution to science, and dates from the year 1800. For many years
it afforded the only means of generating electricity in considerable and
GALVANISM. A-241
manageable quantities. Through its use many of the most remarkable
discoveries were made. In various forms its practical applications have
become so extensive and so common that it is probably the best known
of electrical instruments. Its invention evidently came to Volta through
his reflections upon the contact theory. Believing that electrical separa-
tion takes place when two dissimilar metals come in contact, he thought
to magnify the effect of a single pair by increasing the number. Pairs
of dissimilar metals of like dimensions were bound together by placing a
thin, moist substance between consecutive pairs. Discs of metal, con-
sisting of silver coins and pieces of zinc, and moistened paper, were used,
and, when put together, the pile was formed as shown in the figure.
When this was done, he found it no longer necessary to
use so sensitive an electroscope as the legs of a frog to
detect the electrification. He could himself feel the shock
it produced by touching the opposite extremities of the
pile, and immediately convinced himself of the identity of
electricity with the so-called galvanism. All of the charac-
teristic effects of electricity, as produced by friction upon
glass, sulphur, and other substances, could be shown by
the new instrument. It is interesting to note how
nearly an Englishman—Professor Robinson—came to
hitting upon the same invention. Volta modified the form
of his apparatus by placing the two dissimilar metals
in cups of water, and then joining them together by fig. 37._com-
metallic conductors, thus putting his battery into a plete Pile.
shape which it has retained, practically, to the present day.
The pile shown in Fig. 37 exhibits the appearance of the instrument
called the column-pile, which has to-day but an historical interest. It is
a pile of discs, and the figure here represented is a, facsimile of the first
cut published of the battery.]
First Idea of the Pile, or Battery.—If you immerse a thin plate of
commercial zinc into diluted sulphuric acid a very lively action takes
place; the zinc dissolves, and a considerable quantity of hydrogen is
given off. It is, indeed, this process which is generally employed in the
preparation of hydrogen-gas. But if, instead of ordinary zinc, pure zinc
is used, the action takes place very slowly, and the bubbles of hydrogen
remain attached to the plate of zinc and protect it from further action
of the acid. If a wire or thin plate of platinnm be now placed on the
same, as soon as the two metals touch at one point the action becomes
extremely energetic; the zinc dissolves and hydrogen is given off, but
from the platinum, and no longer from the zinc.
As soon as the contact of the two metals ceases, all action upon the
zinc and all giving off of hydrogen are suspended. This important experi-
ment is to be credited to De la Rive. It throws much light upon all
1 In my historical sketch I have described the origin of the voltaic cell, etc.
16
A-242 bleyer.
that follows. It is equally successful when you substitute for the
platinum silver, copper, or even iron, and gives the same result when the
metals have their points of contact either in the liquid or out of it.
De la Rive's experiment shows that if two metals were to have
their point of contact not in the liquid, but out of it, as Fig. 38 represents,
the chemical action still takes place in
the liquid, as stated above. It also
takes place if, instead of bringing the
two plates of metal into direct contact,
you put one upon the upper part of
the tongue and the other upon the
under part, when you will experience a
slight sensation, like that of a feeble
electric shock, and a peculiar taste will
also be noticeable.
If you place upon the dry part of
the zinc a strip of paper dipped in
iodide of potassium, and then touch
this dampened paper with the platinum,
a blue spot is immediately produced,
which shows that the iodide has been
decomposed and the iodine set free.
These experiments can also be made if
you attach to the zinc and platinum two wires, and operate with the two
loose ends. If you place one of these in the neighborhood of a freely-
suspended magnetic needle, you will notice that the needle will deviate
slightly from its north-south direction
as soon as the contact is established
between the two loose ends of the
wires.
These observations prove that a
singular phenomenon is established by
the co-operation of the two wires, which
is the cause of various actions,—physio-
logical (upon the tongue), chemical
(upon the iodide of potassium), mag-
netic (upon the needle).
The two metal plates immersed in
the liquid are called electrodes, and the
wires, long or short, which are attached
to the electrodes, and which permit the transference to a distance of the
effects produced by the battery, are called rheophores. The rheophores
are generally short, and often end in a longer wire, to which the name
of conductor is given.
The term " circuit " of the current is applied to the whole, formed by
Fig. 39.
GALVANISM.
A-243
the battery, the rheophores, and the solid or liquid conductor through
which the current passes. Every apparatus which produces a current is
a battery.
It is said that the circuit is open when at any point whatever the
conductor be disconnected, as then all the effects of the current cease
and the current does not circulate. The current is closed when the two
parts of the conductor, which were separated, are brought into contact
with each other and the current commences to flow.
It is said that a battery is in short circuit when the conductor con-
necting its poles has a null resistance ; that is, when it is very short. It
has thus come to be said that, in the conductor, the current flows from the
positive pole of the battery {-\-plate of copper) to the negative pole
(—plate of zinc) ; a transference of a peculiar fluid from one to the other
of these points being thus implicitly admitted*. Let us say, in passing,
that this way of looking at things, after having been abandoned in
science, shows a tendency toward re-acceptance, with a few changes; so
that the conventional language, which had not been changed, finds itself
again in accordance with the theoretical ideas admitted.
The cell formed of the electrodes of zinc and copper, immersed in
sulphuric acid, is more particularly known under the name of volta. By
changing the nature of the liquid and the electrodes, an indefinite number
of cells which produce the same kind of energy can be obtained.
Chemical Reaction in the Simple Voltaic Cell.—If we suppose that
the arrangement of metals and acid in the cell is as follows:—
Zn | H2S04 | H2S04 | Cu
Zinc. Sulphuric acid. Sulphuric acid. Copper.
then the operation, which repeats itself over and over when the two
metals are electrically connected, may be represented thus :—
,--------*-------->
Zn | H2S04 | H2S04 | Cu
>---------------v--------------- >--------------r-------------->
--------->
giving Zn S04 | H2S04 | H2 | Cu
Zinc sulphate. Sulphuric acid. Hydrogen. Copper.
The arrow represents the direction of the current through the cell.
The zinc and hydrogen are both placed in the direction of the current,
while the so-called " sulphion," or S04 part of the acid, is displaced in
the other direction. All metals and hydrogen are electro-positive, and
travel in an electrolyte with the positive current. Zinc sulphate is
formed at the expense of zinc and sulphuric acid, and hydrogen-gas is
set free at the copper plate. The simple chemical action taking place is
the displacement of the hydrogen of the acid by zinc, forming zinc
sulphate in place of hydrogen sulphate.
A-244
BLEYER.
Inconstancy of the Simple Voltaic Cell.—It is found that all cells
formed of two electrodes immersed in a liquid present an immense draw-
back ; namely, their action decreases very rapidly from the beginning of
the action. There are two causes for this decrease, of which the follow-
ing is an analysis :—
The first is the loss of acid from the dilution. It can be easily
understood that water acidulated in the proportion of 1 to 100 will act
less energetically than water acidulated in the proportion of 1 to 10.
This cause of the weakening of the battery is not felt until the expira-
tion of a certain time, and it is easily avoided by adding, from time to
time, acid to the dilution.
The second is the deposit of hydrogen upon the copper; If the
current be interrupted during a length of time sufficient for the freeing
of the hydrogen, it will be seen, as soon as the current is again closed,
that the intensity assumes its original vigor.' It suffices, indeed, to agi-
tate the plate of copper, in order to cause the gas to free itself and to
give to the current its initial intensity.
Constant batteries are those in which this second cause of weaken-
ing, called polarization of the electrode, is removed. The presence of
hydrogen upon the electrode opposes a double resistance to the passage
of the current, a passive resistance and an active resistance; it is the
latter which is properly called polarization of the electrode. To depolarize
the electrode is to provide against these resistances by suppressing the
freeing of hydrogen.
In understanding perfectly everything pertaining to this question,
therein will be found lies the whole difficulty concerning the improve-
ment and perfecting of batteries.1
Various reasons have combined to designate the positive electrode
as that one which represents the negative pole of the cell (zinc in Volta's
battery), and the negative electrode as that one which represents the posi-
tive pole. (Copper or platinum in the cells which have occupied us to
the present.)
One of these reasons has already been indicated, which is that the cur-
rent enters the liquid of the battery by the negative pole and goes out
by the positive; in other words, the positive electrode is that by which
the electricity enters-the cell.
In order to avoid difficulty in the choice of these denominations, one
may, in speaking of them, call them the positive pole and the negative
pole, when desirous of designating the corresponding electrodes accord-
ing to the custom of practical men. But, if one wish to employ abso-
lutely correct and scientific terms, great care should be taken in the
application of them, in order to avoid the confusion consequent upon an
awkward attempt at precision in language. Daniells gives in his work,
" Introduction to Chemical Philosophy," another denomination, which
1 Elementary Treatise on Electric Batteries. Alfred Niaudet, France.
GALVANISM.
A-245
ought to be employed more frequently than it is, because it presents the
expression of a fact, and does not depend upon theoretical ideas. He
calls the generating electrode that one which plays a part in the chemical
action; while it is the zinc in the cell which we have considered. He
designates as the conducting electrode that one which is not attacked, but
which serves, however, to complete the cell. He adds that the first may
also be called soluble electrode.
Battery Cells Joined in Intensity.—I have described the most simple
cell that can be prepared, composed of two electrodes of copper and zinc
immersed in acidulated water. The cell of Volta's column-battery does
not differ essentially from this one ; it is composed of two discs, one of
copper and the other of zinc, separated by a circular piece of cloth, satu-
rated with acidulated water.
Volta discovered, by delicate means, that the force of the current in-
creased as the number of cells was augmented, and one of the most bril-
liant discoveries of modern times was the result. He thus showed that
it was possible to add one source of electricity to another and to still a
third, in such a manner as to obtain a multiple source of an indefinitely
increasing power.
The Voltaic Battery and its Offsprings.—The batteries known as the
column, Volta's Couronne de Tasses, Cruikshank's, Wollaston's, Spiral,
Munke's, and Sand's,—all these differ only in their arrangement from that
of Volta's ; in every one we find the zinc, the copper, and the water
acidulated with sulphuric acid.
It will be found that the chemical action is the same in nearly all
batteries : dissolving of one metal, freeing of another. In all forms of
Volta's battery hydrogen-gas is given off and the zinc will be dissolved
without closing the circuit; that is, without the production of electricity
by the battery. This is one of the greatest faults of this battery. It is
consumed without doing any useful work. In most batteries the same
difficulty is presented, with, however, a few exceptions.
General Remarks upon Batteries.
Ideas upon Electric Resistance.—The most simple way of showing
the passage of electric currents in a conducting body is to bring its force
to bear upon the magnetic needle. For instance, let us suppose that the
conductor of a galvanometer, or of a simple detector, be inserted in the
circuit of the current of a battery, and that the deflection of the needle
be 25 degrees. Now, if the circuit be lengthened by the addition of a
wire, the deflection will be seen to diminish to 15 degrees; and if the
circuit be made still longer, the deflection of the needle will not exceed
10 degrees. We may thus draw the following conclusions :—
1. The intensity of the current is less in the second instance than in
the first, and less in the third than in the second.
2. The influence of the additional wire being only passive, the reduc-
A-246 BLEYER.
tion of the intensity of the current is due not to the decrease of the
generating force, but to the increase of the resistance.
These experiments give a practical idea of the resistance that con-
ducting bodies offer to the passage of currents ; and they also demonstrate
that the resistance of a conductor increases with its length. Very exact
and oft-repeated measurements have proved that the resistance of a con-
ductor is in proportion to its length, and in an inverse proportion to its -
sectional area. These laws can be found in all works upon physics.
General Remarks on Electro-motive Force and Resistance.
In all machines in motion is seen a power or cause of movement, and
there are also resistive forces which tend more or less to slacken this
movement or to stop it altogether. For instance, to illustrate this by a
windmill. The large arms, under the pressure of the wind, cause the mill-
stones which crush the grain to turn. In the working of the mill we see,
first, a power,—the wind,—which produces the movement; then there is a
resistance offered by the grinding; this resistance moderates the pace of
the arms, and if the wind falls it stops them entirely. At first sight there
are two mechanical elements apparent: the power, or cause of movement,
or motive force ; and the resistance, or work. A careful examination will
show, however, that the resistance is complex; and that offered by useful
work, as the grinding, should be distinguished from that which is the re-
sult of the friction of the different parts of the machine in motion and
of certain secondary phenomena. All practical men know that a badly-
oiled rubbing surface is sufficient to slacken the movement of a machine,
and even to stop it; all know the importance of friction in the different
parts of the machine, and of the stiffness of the belts and ropes. These
inevitable causes of the slackening, which absorb a part of the motive
power at the cost of the useful work desired, are called passive resistance.
Every one knows that these resistances should be diminished as much as
possible, although they cannot be totally suppressed.
Attention is here called to the fact that in many cases no useful
work is done, and that there then remain only passive resistances. If the
miller take away his millstones and still permit the mill to turn, it is evi-
dent that there remain only those passive resistances (friction and others)
which are produced by the machinery remaining in motion. If all the
machines of a large factory be disconnected from the motion-giving steam-
engine and the engine continue to turn, there will only be present the
motive force furnished by the engine itself and the passive resistances
existing in the engine, in the shafts, and in the different agents of the
transference of the movement which still remain in motion. If now the
steam-engine run entirely alone, not being connected with any shaft or
any piece of machinery outside of itself, we have not only the example of
a system in which there are force and passive resistance, but also that
GALVANISM.
A-247
particular instance where these passive resistances are inherent to the
force-giving machine and inseparable from the production of that force.
In a circuit through which an electric current flows the same influ-
ences are to be found; first, a force residing in the battery and called
electro-motive force ; next, the work ; and, finally, the passive resistance.
The work may be found in the movement of the clapper-spring of an elec-
tric bell; it may be in the movement of a telegraph instrument placed at
a great distance from the battery; it may be in the movement of an
electro-motor or an electro-magnetic machine which lifts a weight; it may
be in a chemical decomposition, produced by the passage of a current in
the production of heat,
and consequently of light,
in a voltaic arc, etc.
Passive resistances
are the results of the cir-
culation of the current in
the different parts of the
circuit. We have ex-
plained how their exist-
ence may be ascertained,
and we have designated
them by this one word,
resistance. If the current
produce no real work,—
that is, if the circuit is
composed solely of con-
ductors, without the interposition of any apparatus which puts the cur-
rent to any use,—the resistance is entirely passive. These considera-
tions explain and justify the use of the word resistance applied to that
property of reducing the intensity of the electric current which the con-
ductors possess.
Electro-motive Force.—The cause which produces the electric current
we have called electro-motive force. In order to give a clear idea upon
this point force, we will adduce several experiments:—
If a battery cell be taken and the current which it produces caused
to act upon a galvanometer, we shall then see that the needle is deflected;
for instance, toward the right. If we change the communications of the
battery with the galvanometer the direction of the needle's deflection will
be altered, which shows that the direction of the current in the galva-
nometer has been changed,—if we now consider the first conditions : the
needle deflected toward the right.
If now a second battery cell, differing in no way from the first, be
taken and inserted in the circuit, and the negative pole of this second
attached to the positive pole of the first, the two currents will flow in the
same direction and join each other; we find that the intensity of the re-
A-248
BLEYER.
suiting current is increased, and consequently the deflection of the needle
is greater. In these conditions the two battery cells are joined in inten-
sity, forming (Fig. 40) a battery of two cells. A battery of any number
of cells could thus be formed, as stated before, but this is not the point
upon which we wish to insist; we desire only to call the expression battery
cells joined in intensity, and to determine the exact meaning.
Suppose that we now insert a second cell in the circuit of the first,
but uniting the positive pole to the positive pole and the negative to the
negative in such a manner as to have two poles of the same name ending
at the galvanometer (Fig. 41).
Under these conditions the needle will remain stationary. This is
not to be wondered at if it be remembered that the two cells tend to
fig. 41.
produce equal currents in opposite directions. The fact that these cur-
rents balance each other and that there is no movement either in one
direction or the other is quite natural. It is said in this case that the
two battery cells are opposed to each other, or are joined in opposition.
We have assumed, in the above, that the opposed cells were of equal
dimensions. Each one acting alone would produce the same deflection
of the needle, one toward the right and the other toward the left; both
acting simultaneously in opposite directions cause no deflection whatever,
which is quite natural and easily understood. Let us vary the experi-
ment, and place in the same circuit (Fig. 42) a small voltaic cell, in oppo-
sition to a larger one of the same nature. We find that the needle will
remain stationary, thus showing that there is no current. This result
will appear strange to the uninitiated reader, and deserves to be dwelt
upon. If made to act separately, they cause the needle to deflect, one
GALVANISM.
A-249
toward the right, the other toward the left. The current furnished by
the larger one is more intense than the current produced by the smaller
one, as the deflections of the needle show. But if these two cells be
opposed to each other, the effect of one is counterbalanced by the effect
of the other, and no current flows through the circuit. The conclusion
of this experiment is that the electro-motive force of battery cells does
not depend upon their dimensions. Experiments also show clearly that
the electro-motive force of battery cells does not depend upon their
dimensions, but upon the materials used in their composition.
Measurement of Electro-motive Forces.—It has been seen how, by
means of an ordinary galvanometer, the electro-motive forces of different
Fig. 42.
batteries maybe compared. This method,just used and described, is
called the method of opposition, because it consists in opposing equal
or unequal forces. It can be easily understood how the electro-motive
forces of different cells may thus be measured and tables of these forces
made out. The electro-motive forces inserted between two dissimilar
metals are altered by every change in their temperatures, but the con-
nection between the change of temperatures and the change of electro-
motive force has not been thoroughly investigated.
Electro-motive force may also be produced by electricity in motion,
and by magnetism in ways which we cannot even describe, until the
simpler phenomena of electricity in motion and of magnetism have been
described ; but it may be said generally that all causes which have the
A-250
BLEYER.
power of altering the distribution of electricity can produce electro-
motive force or difference of potential. Every source of electricity must,
as such, be able to produce a difference of potential; since no charge of
electricity whatever can be made sensible without some difference of
potentials, between the charged body and the earth, of neighboring con-
ductors.
Internal Resistance of the Battery.—From the foregoing remarks it
has been seen that the conductors outside of the battery offer a certain
resistance to the electric movement, or, in other words, a resistance to
passage of the current. Experiments show that the battery itself offers
a resistance to the current it produces. From several of these obser-
vations it has also been concluded that batteries have an internal resist-
ance in themselves, and that the resistance increases with the distance
between the electrodes in the liquid, and diminishes when the immersed
surfaces are increased.
If the battery be considered as a force-producing machine, it is not
to be wondered at that it at the same time produces force and offers a
resistance to that force. This condition is common to all machines ; a
part of the force they produce is absorbed by those passive resistances
resulting from the action of the different parts of the machine. In a
steam-engine, for instance, the friction of the steam in the pipes, the
friction of the piston in the cylinder, etc., etc., cannot be avoided. This
resistance of the battery has to be taken into account in nearly all cases,
for the explanation of phenomena and for the calculation of results.
It can be seen that, of two batteries in which the electrodes are of
unequal dimensions, the distance between them being equal in each, the
one having the larger electrodes offers less resistance than the other; and
it can be said, in general, that larger cells, when compared with smaller
ones, offer less resistance, because the increase of surface of the electrodes
is greater than the increase of the distance between them. This resist-
ance of the batteries varies with the nature of the liquids in which the
electrodes are immersed. It can be easily understood that all liquids
have not the same specific power of resistance.
Connection of Voltaic Cells Abreast.—We have seen (Fig. 41) how
two battery cells of the same kind may be placed in opposition to each
other in such a manner as to counterbalance each other. Let us now
take away the galvanometer that we had placed in the circuit of these
cells, and we shall still have two cells joined in opposition.
Let us consider the two cells thus joined. If the galvanometer be
put into communication, on one hand, with the wire connecting the two
positive poles and, on the other hand, with the wires connecting the two
negative poles, the passage of a very strong current will be observed.
The currents of the two cells, which were at first opposed to each other,
now flow together in the galvanometer. The two battery cells are then
said to he joined in quantity.
GALVANISM. A-251
The metallic piece which connects the two zinc poles may be consid-
ered as the negative pole common to both cells and the other as the
positive pole common to both cells. It may be observed that the two
cells ought to produce the same effects as a single one, in which the
electrodes would have a double surface, while the distance between them
would remain the same.
The internal resistance offered by the two cells is only half of that
offered by each one alone, while the electro-motive force remains the
same. This may be demonstrated by placing a third cell, of the same
size and kind, in opposition to these two cells joined in quantity. The
galvanometric needle does not deflect, which shows once more that the
electro-motive force does not depend upon the size of the electrodes, but
solely upon their nature.
There is, finally, a third way of joining these two cells, namely,
joining them in intensity, of which we have already spoken. This
manner consists in uniting the positive pole of one of the cells to the
negative pole of the other. In this arrangement the electro-motive force
Fig. 43.
of the two taken together is double that of each separately; the resist-
ance is also double.
These different ways of joining battery cells may be applied to any
number of cells. If six cells be taken, for instance, and joined in
intensity, the electro-motive force of one cell being symbolized by E
and its resistance by R, it is evident that a battery of six cells joined in
intensity will have an electro-motive force equal to 6 E and a resistance
equal to R. If all be joined in quantity (Fig. 43), the electro-motive
force of the battery will be E and the resistance —
6
If they be joined by twos in intensity and threes in quantity, the
electro-motive force will be 2 E and the resistance § R. They may,
finally, be joined by threes in intensity and by twos in quantity; the
electro-motive force will be 3 E and the resistance § R. As long as, in
the last combination, there is no connection with any outside circuit, the
three cells on the right are in opposition to the three on the left. It is
not necessary for me to dwell longer upon the subject, or to make calcu-
lations which are, indeed, very simple, to enable the reader to understand
A-252
BLEYER.
that, with a sufficient number of cells, a battery may be as great, and
its resistance as little, as may be desired.
Voltameter.—Before entering upon the study of some of the bat-
teries, it would be well to study a few of the effects they produce. Of all
the chemical actions that can be brought about by means of electric cur-
rents, the decomposition of water is the most striking. It is done in an
apparatus called the voltameter.
Two wires or plates of platinum are placed parallel with each other
in a jar containing dilute sulphuric acid. These two electrodes pass
through the bottom of the jar,
and are attached to binding-
screws or terminals to which the
wires of a battery are fastened.
If a sufficiently energetic current
be made to pass in this apparatus,
bubbles of gas will be seen to free
themselves from the surface of
the electrodes. If these gases be
collected in proper gas-measuring
jars, oxygen will be found in one
and hydrogen in the other.
The electrode by which the
current enters the apparatus is
called positive electrode of the
voltameter. It is that which is
connected with the positive pole,
or, in other words, with the nega-
tive electrode of the battery, that
furnishes the current. The nega-
tive electrode of the voltameter is
connected with the negative pole,
or positive electrode or gener-
ating electrode of the battery.
The oxygen which appears'upon
the positive electrode of the voltameter is termed electro-negative; the
hydrogen which is seen at the surface of the negative electrode of the
voltameter is termed electro-positive.
In general, every liquid decomposed by the passage of an electric
current is called an electrolyte, and it is said to be electrolyzed so long as
the electric action continues. Faraday established, by numerous ex-
periments, the laws of definite electrolysis. Without going into details,
suffice it to say that two or three cells joined in intensity produce a
current used to electrolyze water; for instance, for each chemical equiva-
lent of hydrogen set free in the voltameter there will be an equivalent
of zinc dissolved in each cell of the battery. The law of Faraday
Fig. 44.—A Voltameter.
GALVANISM.
A-253
may be said to be the equivalent of chemical work in all parts of the
circuit.
If the experiment be made with six cells, instead of with three as
indicated above, the quantity of hydrogen set free in one minute will be
much greater. An idea of the quantity of electricity is thus obtained,
and it can be understood how the instrument called voltameter permits
one to measure this quantity. It owes its name to Faraday, who was
perfectly justified in so calling it, as it is in truth an instrument of meas-
urement. The same cannot be said of the galvanometer, which it would
be better to call galvanoscope; for, in general, it does not measure the
intensity of the current which passes through it, and it is only by means
of complicated contrivances that any measurements can be obtained from
its indications.
Much to our regret, this instrument (voltameter) is not convenient
for use. It is unreliable regarding the indications, and often produces
false results, on account of the resistance which it introduces into the
circuit. It also presents other causes of error.
It is possible to attach a specially-calibrated scale to a galvanometer
so that the readings shall be brought directly into current. A galvanom-
eter that has been calibrated in this way is called an ammeter (ampere-
meter). From it one can read off the scale milliamperes or thousandths
of an ampere, and often obtain fairly accurate results.
SECONDARY CURRENTS.
Polarized Electrodes.—If the voltameter be submitted for a short time
to the action of a current its electrodes acquire remarkable properties,
which may be recognized in the following manner: If the wires are de-
tached connecting the voltameter to the battery, and then connected with
the voltameter and a galvanometer, the galvanometric needle will be seen
to deflect, thus making manifest the passage of a current furnished b}r
the voltameter. The direction of the current is such as to show that
that which was the negative electrode of the voltameter in the experiment
with the battery has become, in the experiment with the galvanometer, the
positive pole of this new source of electricity. In other words, the cur-
rent flows in one direction in the first case and in the opposite direction
in the second. It may be said that the voltameter has been charged with
part of the current of the battery, and returns this current in the con-
trary direction.
It has been said that the electrodes are polarized ; which is true, for
they have been rendered capable of acting as poles. This is the origin of
the expression which we have already used,—polarization of the elec-
trodes. The current furnished by the polarized electrodes of the vol-
tameter in the conditions indicated above is called a secondary current,
the voltameter acting as a secondary battery. The secondary current
thus obtained lasts but a short time; its intensity is seen to diminish
A-254
BLEYER.
rapidly from the moment it begins to circulate in the galvanometer, and
is soon reduced to nothing.
Polarization of a Voltaic Cell.—Let us now turn to the consideration
of the objections to the earlier forms of batteries. It will not be difficult
to understand the origin of their drawbacks, and how they have been
overcome. An ideal battery should maintain a constant electro-motive
force through the whole time of its action; its resistance should be as
slight as possible ; the materials of which it is constructed should be such
as not to become rapidly changed in their character during its action, so
that its life may be as long as possible; and there should be little or no
chemical action going on when the circuit is broken, so that the entire
energy of chemical change shall be concerned in or incident to the pro-
duction of the current. The first forms of batteries, which were single-
fluid batteries, failed to meet any of these requirements.
The following instructive and striking experiments illustrate to us
the principal difficulty in the way of meeting the first: If the current
furnished by a voltaic cell (one of Wollaston's, for instance), with well-
amalgamated zinc, be examined by means of a galvanometer, the inten-
sity is seen to diminish from the moment the circuit is closed. This
diminution is very rapid if the circuit have but very little resistance ; it
is, on the other hand, very slow if the circuit offer great resistance. If,
after having allowed the current to flow for five minutes, for instance, the
circuit be left open for five minutes, it will be seen, when again closed,
that the current has nearly assumed its first intensity. It can he said,
then, that the battery when not at work regains its initial power.
From these observations it has been shown how it is possible to use
the sand-battery for a number of years in the telegraph service, the
telegraph lines offering great resistance, but only requiring intermittent
currents. By closer observation we find that, while in the circuit, differ-
ent circumstances of the phenomenon will be seen which will throw a great
deal of light upon the causes to which it must be attributed. At first
bubbles of hydrogen are seen to form themselves upon the copper elec-
trode, as we have already stated ; this will lead to the belief that imper-
ceptible bubbles form themselves upon the entire surface in such a way as
to interpose more or less completely, between the electrode and the
liquid, a gaseous layer. Thus, apparently, the principal cause of the
diminution of the intensity of the current should be sought at the surface
of the copper electrode.
The following experiments will serve to demonstrate this : If, after a
marked diminution in the deflection of the galvanometric needle, the elec-
trodes be shaken without lifting them out of the liquid, the current will
be seen to partly recover the force it has lost. The same is observed if
the liquid alone be shaken without moving the electrodes, and, conse-
quently, without changing the extent of the immersed surface. The
moving of the copper electrode alone will show, as a result, the recovery
GALVANISM.
A-255
of the lost force. On rubbing the copper—without taking it out of the
liquid—with a small brush the same result is noticed.
In these three experiments we find that the disappearance of the
bubbles of hydrogen from the surface of the conducting electrode is
accompanied by a renewal of the intensity of the current. If, on the
other hand, the zinc electrode alone be agitated, no perceptible modifica-
tion in the decrease of the current takes place.
Consequently, there can be no doubt as to the importance of the
phenomenon which takes place on the surface of the copper electrode.
This diminution of intensity just observed may be attributed to two
causes: either to the increase in the internal resistance of the battery, or
to the decrease in the electro-motive force; in fact, the two causes are
present at the same time. That the resistance increases cannot be
doubted, since the active surface of the copper electrode is diminished ;
but a simple and direct demonstration of this does not seem easy to
obtain. That the electro-motive force is diminished is extremely easy to
prove. For this experiment the method of opposition is employed which
we have already described,—and a method which is as convenient for the
comparison of electro-motive forces as are scales for the comparison of
weights.
The instant the electrodes are immersed in the liquid and the battery
begins to work, the electro-motive force attains its maximum intensity.
Take two identical battery cells and close the circuit of one of them for
five minutes, leaving the other inactive. At the expiration of that time,
place the one that has been working in opposition to the fresh one, and
interpose a galvanometer in the circuit, and the result will show the
superiority of the electro-motive force of the fresh cell. If, now, these
two cells be made to act separately, each upon itself,—that is, without
the insertion of any resistance,—for five minutes, it will be found, at the
end of that time, by placing them in opposition, that the second one still
possesses greater electro-motive force than the first one.
It can also be shown that the electro-motive force of a voltaic cell
can, by constant action, be reduced one-half. It is admitted that the
diminution in the electro-motive force of batteries is due to the produc-
tion of an electro-motive force (upon the surface of the negative elec-
trode) contrary to that of the principal current. This view is founded
upon the facts which have been advanced about the electro-motive force
found in a voltameter, from electrodes of which gases are given off.
It may be shown by a direct experiment that the conducting elec-
trode of a weakened battery has acquired peculiar properties. It is
only necessary to immerse in the liquid a second plate of copper and
to connect the two with a galvanometer. The passage of a current is
thus made manifest, and its direction shows that the copper plate
acts as the soluble electrode, or electro-positive, when compared with
the other, which assumes the part of a conducting electrode, or electro-
A-256
BLEYER.
negative. This current decreases from the moment it is established, and
soon becomes imperceptible. Thus the electrode which was electro-
negative in the voltaic cell before and during its weakening is electro-
positive in the test-cell of two copper electrodes. Finally, if after the
above experiment the voltaic cell be re-established, the electrode assumes
its original intensity, at least for a moment, and then begins to weaken
again, as in the first instance.
It is then that the conducting electrode is said to be in a state of
polarization. Such is the phenomenon of the polarization of the nega-
tive electrode of batteries, a knowledge of which is so important. We
know that the slighter the polarization the better the battery. There is
still much scope for improvement in batteries, although much attention
and ingenuity have been concentrated upon securing for them constancy
of current and absence of polarization. The principal aim of inventors
has always been, and still is, to depolarize the electrode.
It has been established that the polarization remains the same when
the size of the cell and the intensity of the current are in proportion to
each other. It is here necessary to define polarization. Polarization is
the difference between the electro-motive forces in a polarized battery and
the electro-motive forces in a depolarized battery.
It can be understood, indeed, that the quantity of hydrogen given
off upon the negative electrode is in proportion to the intensity of the
current, and that, if this quantity distribute itself upon the surface of
an electrode also proportional, the degree of thickness of the deposit will
be the same over the entire surface, and consequently its intrinsic action
will not have changed. The practical conclusion of this law is that
polarization will be less in a battery having larger electrodes than in one
with smaller electrodes, though the total resistance be the same.
Polarization in a Battery of Several Elements.—So far, each time
the polarization of the negative or conducting electrode of cells has been
spoken of, the existence of one cell only has been tacitly implied ; and,
further, that the current which produced the polarization was the current
of the cell itself. Under ordinary circumstances this is not so ; several
elements are generally joined in intensity, and the current which flows in
each one is furnished by the entire battery.
If we place ten cells, each having ten units of resistance, in a circuit
of one hundred units (total resistance, two hundred units) it is clear that
the current will be more intense than if nine of the ten cells were taken
away; consequently, the current which produces the polarization in each
cell will be more energetic than if there were only one cell. The result
is that its weakening due to polarization is more, marked in cells which
are joined in intensity than in separate cells.
Explained otherwise, when a current passing through a cell is more
energetic than the current which the cell itself produces, the weakening
of the current takes place under the following circumstances : At first
GALVANISM. A-257
hydrogen is given off upon the copper, and produces that which we have
termed polarization of the cell. But afterward, when the greater part of
the acid is converted into sulphate of zinc, the sulphate itself becomes
electrolyzed, and the reduced zinc deposits itself upon the copper. If,
at last, this deposit cover the entire surface of the copper, it can be
easily seen that the two electrodes will become identical, and, conse-
quently, it is no longer a battery cell. Cases have been adduced, experi-
mentally and otherwise, where some cells of a battery not only cease to
produce current in the right direction, but actually produce a reverse
current.
The Study of Batteries and their Classification.
We have now reached a point where it is possible to study the differ-
ent batteries and to draw comparisons between them. Up to this time we
have studied only the voltaic battery and the modifications in its arrange-
ment. Let us now take a look into those batteries, which have sprung up
from the first cell, analogous to, but differing more or less from, its germ
(the voltaic cell).
It will be seen how Volta, notwithstanding his imperfect means, had
the happy thought to choose the elements which have been used ever
since.
What are the essential conditions of a good galvanic cell? 1. It
should have high electro-motive force. 2. It should have low internal
resistance, so that no energy should be wasted within the cell. 3. It
should give a constant current, and thereby prevent polarization. 4.
The material for its consumption should be cheap and readily obtainable.
5. The cell should require no inspection or supervision to keep it in good
order until all the energy of its chemical affinities is exhausted. 6. The
form and dimension of the cell should be convenient, and no noxious
chemical products should be formed on it by action.
No battery or one form of cell fulfills all these conditions; but as there
are many varieties, it is possible to select certain cells as especially adapted
to particular purposes and compare them by their standard. A great
many cells have been devised from time to time, and, in order to place
them in their proper category, it is necessary to classify them. The
following is the latest scientific classification: 1. The closed-circuit bat-
teries. 2. The open-circuit batteries. 3. Batteries without a depolarizer.
4. Standard of electro-motive force.1 5. The storage battery. 6. The
medical galvanic batteries of several makes.
What is the distinction between an open- and closed- circuit battery ?
It has been seen2 that the inconstancy of the current furnished by a bat-
tery through a fixed resistance is largely accounted for by polarization
' Several specimens of each of the classified batteries will be described and studied.
3 Some of these descriptions of cells are taken from the valuable little work on Primary
Batteries, by H. S. Carhart, A.M., of Michigan. 1891.
17
A-258 BLEYER.
due to cell. That which stops polarization, either by removing the
hydrogen as fast as it is formed or by preventing altogether its dis-
engagement, is called a depolarizer. The distinction between open- and
closed- circuit batteries depends chiefly upon the nature and action of
this depolarizer.
A batter}- is entitled to be included in the closed-circuit type only
when it is capable of working in a closed circuit of moderate resistance for
a considerable period with but slight diminution in the intensity of the
current. The difference is thus clearly established, between it and those
cells that are adapted to stand on open circuit, without wasteful local
action, and that furnish current only at intervals and then only of a few
seconds' duration.
In a closed-circuit cell the depolarizer must act with sufficient
promptness and efficiency to completely prevent polarization, thus
removing this cause of the decrease in the current.
In open-circuit batteries the depolarizer may, indeed, be entirely
absent, or it may act with so much sluggishness as to be unable to pre-
vent polarization taking place to some extent during the action of the
cell, but it destroys polarization after the circuit has been again opened.
The promptness with which a cell recovers from a depression of its
electro-motive force by polarization is a good criterion of the efficacy of
this class of depolarizers. Batteries provided with such depolarizers
occupy an intermediate position between those with a promptly-acting
one and those with none at all, of which the simple voltaic element is
the type. The more-efficient depolarizers, in general, are liquid ; the less-
efficient or slower-acting ones, with only a few exceptions, are solid. . The
first class must be employed when a continuous current is required, espe-
cially if the current is of considerable strength. If but a small current
is taken from a cell through a high resistance, then a solid depolarizer
will suffice. But batteries with no depolarizer for the.removal of hydro-
gen, or an equivalent, are adapted only to open-circuit use, in which the
circuit is to be closed for only a few seconds at a time.
CLOSED-CIRCUIT BATTERIES.
The Daniell Battery.—This is the battery which claims for itself the
underlying principle of all constant batteries. It was invented by Pro-
fessor Daniell, of Edinburgh, in 1836. It (Fig. 45) consists of a copper
plate, G, dipping into a solution of copper sulphate contained in a glass
or glazed, highly-vitrified, stone-ware jar, J, and a zinc plate or rod, Z, to
which a copper wire or strip, W, is soldered, dipping into either dilute sul-
phuric acid or a solution of zinc sulphate, the two solutions being separated
by a porous partition, P, made of unglazed earthenware, and called " a
porous pot." The electro-motive force of a Daniell cell, with all its modi-
fications is, roughly, 1.1 volts, but it varies from about 1.07 volts to 1.14
volts, depending upon the densities of the solutions of copper and zinc
GALVANISM.
A-259
*^
Fig. 45.—Daniell Cell.
sulphate. With equidense solutions and with plates of pure zinc and
copper, the electro-motive force is 1.104 volts. This value is increased by
increasing the density of the copper-sulphate solution, and is diminished
by increasing the density of the zinc-sulphate solution, and is scarcely
at all affected by the ordinary atmospheric
changes of temperature.
The Daniell battery gives a constant
electro-motive force, and retains a nearly
constant resistance. The resistance of
the cell varies with the area of the copper
and zinc plates immersed in the liquid,
the distance between the plates, and the
thickness and constitution of the walls of
the porous cell. With a cell about seven
inches high, of the relative dimensions
shown in the accompanying figure, the re-
sistance may be as low as ^ ohm when the
solution in which the zinc plate is immersed
is dilute sulphuric acid of a specific gravity of about 1.15 at 15° C,
while some Daniell cells with porous pots and small zinc plates are used
having a resistance of as much as 10 ohms. The electro-motive force of
the Daniell, or of any other form of cell, is quite independent of the size
of the various parts of the cell, or of the cell as a whole, and depends
solely on the materials employed in its
construction.
On account of the constancy of the
Daniell cell, which is caused by electro-
motive force, in the practice it may be
taken as a unit and can be compared with
others. The British Association has
adopted a unit differing very little from
this one, and has given to it the name of
volt. The cell in which the electro-motive
force is exactly equal to the volt differs
but slightly from that of Daniell.
The Gravity Battery.—This battery
is a simple modification of the Daniell,
designed to dispense with a porous cup.
It takes its name from the fact that in it
the zinc and copper sulphates are sepa-
rated by their difference in density. One
form of this battery is shown in Fig. 46. This cell alwaj^s keeps in
better condition if a closed circuit be maintained through a high resist-
ance when the battery is not in use.
The Grove Battery.—The Grove battery consists of a cleft cylinder
Fig. 46.—Gravity Battery.
79501397
A-260
BLEYER.
Fig. 47.—Bunsen Battery.
of zinc immersed in dilute sulphuric acid (1 to 12) and a thin plate of
platinum in nitric acid, contained in a porous cup. The platinum elec-
trode, being surrounded by the nitric acid, decomposes, oxygen is set
free and forms water with the polarizating
hydrogen, and nitric oxide is given off. The
battery thus modified is without polarization ;
in other words, it is constant. This battery
dates from 1839.
The Grove battery has the advantage of
electro-motive force and low internal resistance.
Such a cell is capable of giving 12 amperes on
short circuit, or through an external circuit
of no appreciable resistance. Before the intro-
duction of dynamo-electric machines and the
storage battery, 40 Grove cells served for an arc
light. It is found that electro-motive force is
intermediate between that of a Grove and that
of a Daniell battery.
The Bunsen Battery.—After the invention
of the Grove battery, Bunsen modified it by
substituting a prism of baked carbon for the
platinum. The electro-motive force is slightly less than that of the
Grove.
The Bichromate Battery.—This battery is employed very extensively
in laboratories, and presents some very great
advantages. The resistance is very slight on
account of the short distance between the elec-
trodes, and, moreover, the waste of the zinc is
suppressed during the intervals between experi-
ments, as it is withdrawn from the liquid;
thirdly, polarization is slackened by the com-
paratively large surface of the carbon electrode ;
fourthly, the quality of the liquid is consider-
able on account of the special form of the
lower part of the bottle; and, lastly, the charg-
ing and cleansing is extremely easy. But in
spite of these advantages the battery gives a
powerful current for only a short time, after
which the intensity is seen to diminish. It is
therefore suitable only for experiments of short
duration.
The accompanying cut represents one of
the forms of this cell. The zinc is attached to a rod, A, by means of
which it can be drawn out of the liquid when the battery is not in use.
The carbon plates are fastened to a metallic clamp, which is attached to
Fig. 48.—Bichromate
Battery.
GALVANISM.
A-261
the hard-rubber top of the cell. The top of the zinc is covered with an
insulating strip to prevent direct contact with the carbons. Many other
forms of plunge batteries have been the outcome of this invention.
The Copper-Oxide Battery.—It has been remarked that, in general,
the best depolarizers are liquid. There are, however, two exceptions to
this, which exhibit notable efficiency. They are the oxide of copper and
the chloride of silver. Both these solids readily give up their non-metallic
element to nascent hydrogen, and the reduction to the metallic state
makes them excellent conductors.
This copper-oxide cell was intro-
duced by Lalande and Chaperon.
It has a capacity for work per unit
weights greater than any other
cell, either primary or secondary.
Mr. Thomas A. Edison, rec-
ognizing the good qualities of
the copper-oxide as a depolarizer,
has devised a form designed to
meet most of the objections which
may be made to it. The copper
oxide is employed in the form of
a compressed slab, which, with its
connecting copper support, serves
also as the negative plate. Two
of these plates are inclosed in a
copper frame, on the longer arm
of which is the binding-post. One
or two of these copper-oxide
plates are used, according to the
size and capacity of the cells.
The weight of the oxide plate for
a 15-ampere-hour cell is two
ounces, and for a 600-ampere-
hour cell two pounds. The figure, as shown, is a 600-ampere-hour cell
complete. The cover is porcelain, with small openings for the zinc and
copper terminals. Since this cover does not exclude the air, the forma-
tion of a carbonate is prevented by pouring on top of the solution of
caustic potash a small quantity of heavy paraffin-oil, so as to form a layer
about one-fourth of an inch deep. If it is not used, the life of the cell
is reduced fully two-thirds.
The Edison-Lalande cell has been subjected to a number of stringent
tests at the Edison laboratory,1 and is also being put to the test of doing
' The cuts and notes illustrating these laboratory tests of the Edison-Lalande battery are
taken from the private laboratory register of Mr. Edison. I found it important, to introduce
these detailed accounts of this cell, that every one might judge its value for himself. It is the
only perfect closed-circuit battery in existence, and can be highly recommended to the profes-
sion for all medical and surgical purposes.
Fig. 49.—Edison-Lalande Copper-
Oxide Battery.
A-262
BLEYER.
hard and continuous work on the lines of telegraph, railway, and tele-
phone companies, with the best of results. This battery is now in the
hands of the most prominent men of our profession for all kinds of work.
I can recommend it as the only battery for cautery and motor work.
Those who have not seen it in action should certainly find an opportunity
to examine it. The only drawback is in the cleansing and refilling, in
which caution must be exercised on account of the caustic potash,
although this difficulty is now being overcome by using sticks instead of
a solution of potash. The results of these laboratory tests are shown in
the curves given herewith (Fig. 50).
0T8r64,0r8
COMPARATIVE TEST OF TWO EDISON-LALANDE CELLS, TYPE A (JOINED IN SERIES),
AND ONE LECLANCHE CELL (BOTH FRESHLY PREPARED).
——— Edison-Lalande Battery ------1— —Leclanche Battery,
TIME IN HOURS
In this test the batteries were so arranged as to be alternately thrown
into circuit with a resistance coil. The periods of rest and work were of
five minutes' duration. When the Leclanche was resting the Edison-
Lalande was working, and vice versa.
The 300-ampere-hour cell, which may be taken as a typical example,
stands eleven and one-fourth inches high by five and three-eighths inches
in diameter. It has an internal resistance of 0.025 ohm; the electro-
motive force of the cell on continuous hard work is 0.1 volt, and on light
work 0.15 volt. The initial electro-motive force is 0.9 volt, soon falling,
however, to the normal standard, where it remains practically constant
during the life of the cell. On open circuit there is little or practically
no action on the zinc, and positively none when the latter is pure. The
GALVANISM.
A-263
action of the cell is admirably shown in the accompanying curves (Fig.
51). Fig. 52 represents the results of careful tests made at the Edison
laboratory upon cells picked out at random from among a large number.
in this test four 300-ampere-hour cells were joined in series in circuit with
a resistance of 0.8 ohm, and gave the following results: Weight of zinc
before test, 10,017 grammes; weight of zinc after test, 8567 grammes;
total loss, 1450 grammes. Calculated loss from output, 1444 grammes;
loss by local action, 6 grammes. Mean current, 2.76 amperes, 2.8 volts;
total run, 298 ampere-hours. The loss was calculated as follows, taking
the chemical equivalent of zinc as 0.0003367, based on the latest researches
3;2
COMPARATIVE TEST OF SAME CELLS USED IN PREVIOUS TEST AFTER BEING
FILLED WITH .FRESH SOLUTION, THE PLATES REMAINING UNALTERED.
Edison-Lalande Battery ———.—Leclanche] Battery
TIME 114 HOURS
64 6.8
of Rayleigh and Kohlrauch: 276 X 108 X 3600 X 0.0003367 = 361 ;
361 X 4=1444.
Fig. 53 exhibits results of a comparative test of Leclanche and
Edison-Lalande batteries in connection with Blake transmitter. Both
batteries had been closed through transmitter for twenty minutes; the
circuit was then opened, and the increase in electro-motive force was noted
at regular intervals.
The test as here shown extended over a period of one hundred and
eight hours, and both the current and electro-motive force remained
practically constant. It will be noted, however, that the external avail-
able energy continued to increase for nearly half the period of the test,
owing to the almost constant decrease in the internal resistance of the
A-264
BLEYER.
cell, which is also evidenced by the curve representing the internal
energy, which fell rapidly from the start.
This decrease in internal resistance is due to the fact that the reduc-
tion of the oxide of
metallic copper at the
surface of the nega-
tive plate causes the
formation of an excel-
lent conducting sur-
face, the production
of which, however, re-
quires a few hours'
work in a cell freshly
set up. In the latest
form of the Edison-
Lalande cell the im-
provement has been ef-
fected of reducing a
thin film of copper
on the oxide super-
ficially, before placing
in the cell, to make
the initial internal re-
sistance lower. In
reading the figures at
the left those referring
to the watts, ohms,
and volts must be di-
vided by four in order
to reduce them to the
corresponding values
for one cell. During
the test the cells were
connected through a
resistance of 0.8 ohm.
I am convinced
that wherever this
battery is used it will
prove itself possessed
of undeniable advan-
tages over all others.
The Chloride-of-Silver CWZ.—JMarie Davy appears to have been the
first to suggest the use of silver chloride as a depolarizer (about 1860),
although it owes its present prominence to the investigations of Warren
de la Rue.
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