THE INDUCTION COIL; 
ITS 
Varieties and the Differential Indications 
for their Use. 
BY 
A. D. ROCKWELL, A.M., M.D. 
NEWYORK. 
/» * </•/ 
Reprinted from The Medical Record, November 8, 1884. 
NEWYORK; 
TROW’S PRINTING AND BOOKBINDING CO. 
201-213 East Twelfth Street. 
i 8 THE INDUCTION COIL: 
ITS 
Varieties and the Differential Indications 
for their Use. 
BY 
A. D. ROCKWELL, A.M., M.D., 
NEWYORK. 
Reprinted from The Medical Record, November 8, 1884. 
NEWYORK: 
TROW’S PRINTING AND BOOKBINDING CO. 
201-213 East Twelfth Street. 
ISB4. THE INDUCTION COIL—ITS VARIETIES AND 
THE DIFFERENTIAL INDICATIONS 
FOR THEIR USE.1 
When solicited to contribute something to the annual 
meeting of this Academy along that line of research in 
which I have been interested for so long a time, I hesi- 
tated in the selection of a topic. Of material there is 
plenty, and of sufficient importance. The whole field of 
the physics, physiology, and therapeutics of electricity 
lies open before us. The comparative value of its three 
subdivisions offers a subject for discussion and the rela- 
tion of experiences, while the differential indications for 
the use of these various forms—galvanism, faradism, and 
franklinism—is of still greater importance and even less 
understood. 
Vital in interest as are each and all of these themes, 
and others that occurred to my mind, they seemed to be 
excluded from discussion here, since it has been sug- 
gested that whatever is presented should flavor some- 
what of originality, or at least be not altogether hack- 
neyed ; and these topics have, one and all, been dis- 
cussed at various times in the current medical literature 
of the day, and are more or less fully considered in many 
of the works devoted to electro-therapeutics. The laud- 
able aspiration of this Academy, then, as attested by the 
prospectus lately issued, confirms the aphorism that 
“ originality is a thing we constantly clamor for,” as 
well as “constantly quarrel with.” Unfortunately, how- 
1 Read before the annual meeting of the American Academy of Medicine, at 
Baltimore, October 28, 1884. 4 
ever, pure originality in thought or methods of expres- 
sion is the gift of but few. Old and long-forgotten ideas 
are being constantly rehabilitated and brought forward 
under the guise of new and advanced opinions. In this 
way, much that would otherwise be lost or fall short of 
its proper utilization becomes, through a more persistent 
and perhaps clearer presentation, a practical part of the 
world’s integral store of knowledge. While, therefore, 
none of the facts in physics that I propose here to pre- 
sent are in any sense new, yet there has been no general 
appreciation of them, and but little knowledge, even 
among those who have been endeavoring, in a blind sort 
of way, to utilize them, that such facts existed. 
As to the few statements that are made along the line 
of therapeutics, the most that I can say of them is that 
they are the result of much experience and of very many 
carefully recorded observations, and if presented with 
any measure of clearness ought to be of some little ser- 
vice to those who are interested in but who have given 
little thought to the matter. But to my theme. There 
are two kinds of electro-magnetic machines that are pre- 
sented to the medical men for therapeutic purposes. The 
first is termed a separate coil, and the second a continu- 
ous or single coil apparatus. The separate coil appara- 
tus is the one most commonly used and the one most 
generally understood. The separate coil is the variety 
described and illustrated in every text-book of physics, 
but not in sufficient detail to make clear its mechanism 
when used for medical purposes. Craving the indul- 
gence of those who may be thoroughly informed on these 
points, and who may therefore regard as primitive the 
remarks that follow, let me, bv the aid of the accompany- 
ing diagram (Fig. i), describe the course and influence of 
the electric current in an ordinary separate coil faradic 
apparatus. 
All induction machines are composed of not less than 
two coils. The first or primary coil consists of a large, 
well-insulated wire surrounding a bundle of soft iron wire, 5 
which forms a magnetic centre. Over this first or pri- 
mary coil is wound a coil composed of several convolu- 
tions of fine, well-insulated wire for the induced current. 
Fie. T. 
The terminals of the first or primary coils of wire are 
united, one end to the battery that operates the coil, and 
the other to the part of the automatic rheotome accord- 6 
ing to the following description. As the battery is the 
important factor, let us start from it and follow the con- 
nections and action of the combinations that produce the 
effect: 
The positive pole (P) of the battery is connected with 
the governor marked A (Fig. i). The negative pole N 
of the battery is connected with the first end of the pri- 
mary coil, while the last end of the primary coil is con- 
nected with the spring support B. The electro-motive 
force is conveyed from the battery through the primary 
coil to the spring support B (rheotome), thence to the 
platina-pointed screw of the governor D, and lastly to the 
battery, making the complete circuit. 
In the centre of the coil and surrounded by the soft 
iron wires is placed a soft iron rod. One end of the rod 
is bent at right angles, so that the hammer on the spring 
is directly over and can move toward this soft iron rod, 
marked C. When the vibrating spring is resting against 
the platina-pointed screw D and the battery is connected 
with the coil, the current, as it passes over the wire of 
this primary coil, renders magnetic both the centre bun- 
dle of soft iron wires and the soft iron rod. 
The magnetism is of sufficient force to attract the soft 
iron hammer on the spring, and draw it down or near to 
the magnetized rod C. 
This movement of the spring severs the connection 
between the spring and the platina-pointed screw D and 
opens the circuit. The soft iron rod, therefore, loses its 
magnetism. The spring ceases to be held down, its ten- 
sion being sufficient to raise it to a horizontal position, 
where it again rests in direct contact with the platina- 
pointed screw D. Again the circuit is closed and the 
process as described is repeated with inconceivable rapid- 
ity. By the action of the battery current, as it is conveyed 
over the primary coil, and the influence of the magnet- 
ized bundle of soft iron wires, a current is induced upon 
the second coil of fine wire which surrounds the primary 
coil. This power of induction can be established to the 7 
fifth and sixth coil, and further if the magnetic field is 
properly arranged. 
In the ordinary form of induction coil just described, 
the terminals of the secondary or fine wire coil are free 
and in no manner connected with the primary circuit. 
The influence of magnetism produces a current which we 
call pure induced. 
In the continuous coil apparatus, on the contrary, we 
not only receive the inductive influence, but the primary 
influence as well, since it is carried over in combination 
with the induced currents. Although called a continu- 
ous coil, it is really made up of several distinct coils, and 
each successive coil increases in length but decreases in 
thickness. These coils are wound over each other, and 
are tapped at different portions of their length, but, un- 
like other forms, they make direct connection with each 
other. This accounts for an apparent contradiction of 
terms that might prove confusing. 
These coils (Fig. 2) are, for convenience of illustration, 
represented by the upper straight lines I, 11, 111, IV, 
termed, respectively, the primary, first, second, and 
third induction coils. The letters A, B, C, D, E rep- 
resent the different posts of the continuous coil appara- 
tus to which the conducting cords are attached, while 
the numerals 1, 2, 3, 4, etc., indicate the combinations 
by which are obtained ten different qualities of current. 
The short line marked x, starting from A, represents the 
current from the short, thick, primary coil marked I. 
Second line (2), current from the primary and first (I,II) 
induction coils combined. Third line (3), current from 
the primary and first and second (I, 11, III) induction 
coils. Fourth line (4), current from primary, first, sec- 
ond, and third (I, 11, 111, IV) induction coils. Fifth 
line (5), current from the first (II) induction coil only. 
Sixth line (6), current from the first and second (11, III) 
induction coils. Seventh line (7), current from the first, 
second, and third (11, 111, IV) induction coils. Eighth 
line (8), current from the second (HI) induction coil. 8 
Ninth line (9), current from the second 
and third (111, IV) induction coils com- 
bined. Tenth line (10), current from 
the third (IV) induction coil only. 
Therapeutical considerations.—When 
we consider the many combinations that 
are possible in the continuous coil ap- 
paratus and the different qualities of cur- 
rent that result therefrom, its general 
superiority over the separate coil is suf- 
ficiently evident; and this superiority be- 
comes more marked if we examine into 
the varied physical and physiological 
effects produced by these combinations. 
Our object of inquiry, however, is not 
as to the relative merits of different 
machines, but as to the comparative 
value of and the differential indications 
for the use of the various combinations 
of the continuous coil apparatus. This 
point of inquiry, although less important 
than when it relates to the two forms of 
dynamic electricity, is yet of no little 
account, and in some respects has been 
found to be more difficult of solution. 
Fig. 2. 
Notwithstanding the many qualities of 
current that are derived from the con- 
tinuous coil, I have, after much observa- 
tion, reduced to three the number of 
combinations that seem to be worthy of 
differential consideration. 
Every therapeutic result that can be 
obtained by any of the ten combinations 
heretofore considered, will in all proba- 
bility result from the use of some one of 
the following : 
i. The current from the primary coil as 
represented by the line marked i (Fig. 2). 9 
2. The current from the primary and the first and sec- 
ond induction coils in combination, as represented by 
the line marked 3. 
3. The current from the primary and the first, second, 
and third induction coils in combination, as represented 
by the line marked 4. 
The primary coil yields a current of large quantity but 
of small tension, owing to the fact that the wire of which 
the coil is composed is short and thick. It is worthy of 
note, however, that this current has considerable chemi- 
cal power. It will burn iron or steel, giving forth a 
bright deflagrating spark, and will readily electro-plate, 
an effect not obtainable with any of the induction coils, 
either alone or in combination with each other. This 
current is apparently very weak, and induces but slight 
muscular contractions in the healthy person. In occa- 
sional pathological conditions, however, this mild current 
acts with unexpected energy, producing muscular con- 
tractions far exceeding in vigor those that are called 
forth by the stronger action of the induction coils. 
On account of its mild but efficient action the current 
from the primary coil is preferable for applications to the 
head and the more sensitive portions of the body, and it 
will, as a rule, relieve pains of a true neuralgic character, 
and especially when great tenderness exists along the 
course of the nerve, far more effectually than the cur- 
rent from any of the induction coils. It is impossible to 
account for this frequently observed fact, without it be 
ascribed to a combination of the battery and the induc- 
tive influence. When dealing with an agent so subtle 
and so little understood as electricity, it is difficult to ex- 
press one’s meaning in terms altogether satisfactory, but 
that such a combination is active and effective is evi- 
denced by the readiness with which electrolytic effects 
are produced. Asthenopia is a symptom that I have 
known to be greatly relieved and even cured many times 
by electricity, but more especially through the use of 
the primary coil. The tired, aching eye is both tempo- rarily rested after each sitting and permanently strength- 
ened by continued treatment. There seems to be little 
appreciation, either among ophthalmologists or general 
practitioners, of the great relief that may follow this treat- 
ment in the many cases where the eyes ache severely, 
if used even for a little time before breakfast or at twi- 
light, or where neuralgic pains exist in or near the eye, 
or where there is annoyance from muscse volitantes. 
As we include in the circuit with the primary the vari- 
ous induction coils, the current increases in strength 
with each coil that is added. With the addition of the 
first induction coil a much greater strength is apparent, 
but the combination has no marked physical or physio- 
logical effects that need detain us. By including also 
the second induction coil in the circuit, however (line 
marked 3, Fig. 2), we obtain a current of a peculiar and 
unique quality. Like the primary coil, it will electro- 
plate, but unlike it, it will not burn steel or iron. The 
peculiarity of this combination of the coils is that the 
maximum of power to contract muscular tissue is here 
obtained. Each additional coil now that is attached 
simply gives a decreasing contractile power. Why the 
maximum of current strength is reached in the combina- 
tion of the primary with the first and second induction 
coils it is difficult to say, excepting as we ascribe it to 
the law of harmony or polarization that is brought about 
by properly conditioning the magnetic centre of the 
helix, the several coils composing the helix, and the bat- 
tery influence acting upon the coils. The current from 
this combination is not at all pleasant; it is keen and 
cutting in character, and with its strong contractile prop- 
erties it is peculiarly adapted to those cases where pow- 
erful impressions are called for. Hence in not a few 
cases of paralysis where the response to galvanism is 
perfect, but where there is a diminution of farado-mus- 
cular contractility, I have found it preferable to any of 
the other qualities of current to be derived from the con- 
tinuous coil apparatus. 11 
In superficial forms of anaesthesia it is, perhaps, in no 
way superior, but in certain persistent and more deeply 
seated forms of lost or perverted sensibility it is decid- 
edly more efficacious than other combinations. Its 
greater contractile power over muscular tissue, both vol- 
untary and involuntary, renders it more efficacious in 
cases of menstrual suppression, and also for atrophied 
conditions of the uterus, for which so much has been 
done by electrical methods of treatment. In cases of 
dysmenorrhoea, as well as in the various neuralgias, my 
experience leads me to exclude its use. Faradism has 
been used, and with success, to destroy the foetus in ex- 
tra-uterine pregnancy. While I greatly prefer the gal- 
vanic current, having always used it without the slightest 
ill effect, yet if the faradic is employed 1 should not re- 
commend the current from the coils now under consid- 
eration, but the one presently to be described ; for with 
this latter form we obtain effects equally destructive to 
the foetal life and with less violence to the contractile 
tissues of the mother. There are several other differen- 
tial points connected with the use of this series which 
suggest themselves, but they are of minor importance. 
One other condition, however, deserves mention. 
Impaired virility is a defect for which relief is very often 
sought. Its influence upon the mind is most unfortu- 
nate, and it should be understood that electricity is often 
of very considerable benefit in these cases. It is suffi- 
cient to say that no case which is in any way hopeful 
should be abandoned until the current from the primary 
and first and second induction have been tried. 
When we include in the circuit not only the primary 
and the fijst and second, but also the third induction 
coil as represented by the line marked 4, effects are ob- 
tained more interesting and satisfactory than from any of 
the other combinations. 
These effects are pre-eminently tonic and sedative in 
character, and give for this quality of current a range of 
usefulness wider than can be ascribed to the others. 12 
There are but few, in all probability, who at this day are 
unfamiliar with the term general faradization, and who 
do not understand that by it is meant the application of 
the faradic current to the entire surface of the body, 
from the crown of the head to the soles of the feet. It is 
in the operation of general faradization, when we desire 
to obtain the best constitutional tonic effect that elec- 
tricity is capable of giving, that we resort to this com- 
bination of the primary and induction coils. Its action 
on the motor and sentient nerves is less severe, and its 
general effects far more agreeable. For the relief of that 
great army of symptoms that are so familiar and so per- 
plexing to those who have had much to do with neuras- 
thenic cases, there is, according to my experience, noth- 
ing to be compared with it. Even the galvanic current 
by the method of central galvanization, so important in 
its direct effect upon the central nervous system, falls 
short of the therapeutic results that follow well-directed 
applications of general faradization. When persistent 
failure follows endeavors along this line of electrization, 
the cause of failure must be ascribed to hasty and faulty 
methods of administration. In no department of thera- 
peutics is it of more importance to be thorough in detail. 
He only will achieve the best results who appreciates 
this fact, who is willing to inform himself as to the modus 
operandi of the methods, and who will devote in indi- 
vidual cases a reasonable degree of time and patience in 
carrying them out.