Mk« gntt$  at §atur*.
AN
ADDRESS
DELIVERED
BEFORE THE  CHEMICAL  SOCIETY
UNION  COLLEGE,
JULY 22d, 1863.
         /  4f?
    GEORGE F. BARKER, M. D.,

ACTING PROFESSOR OF CHEMISTRY, ALBANY MEDICAL COLLEGE.
,AH(~''
    ALBANY, N. Y.:
J. MUNSELL, 78 STATE STREET.
        1863. 
CORRESPONDENCE.
Prof. G. F. Barker :
  Dear Sir—By direction of the Chemical Society of Union College, we
have the  honor to request for publication a copy of the very able and
pleasing address delivered by you before the Society this morning.
                        Very truly yours,
                                    CHAS. G. CLARK,
                                    WM. APPLETON POTTER.
  Union College, July 22d, 1863.
Messrs. Chas. G. Clark and Wm. Appleton Potter,
                         Committee of the Chemical Society:
  Gentlemen—I  thank  you for  the agreeable manner in which it has
pleased you to request for publication a copy of the address delivered be-
fore your Society.  If you deem  the few thoughts  so hastily thrown to-
gether to be worthy the honor you ask for them, I can only reply that, as
they were prepared for the Society, they are its property, and I cheerfully
place them at your disposal.
  Congratulating you upon the vigorous condition of the Chemical Society,
                      I remain, gentlemen,
                                Most truly yours,
                                            GEO.  F. BARKER.
  Albany, July 25, 1863. 
NATURE'S FORCES.
  Truth is eternal.   Its principles can never be in conflict
with each other.  But the mistaken notion has arisen in
the community that to account for natural phenomena by
second causes, derogates from the character of the great
First-cause.  Now, the fact that Deity works by means, is
proved alike in nature and in revelation ; and these means
are the second causes referred to.  But the Divine energy
is not wasted ; it never provides competent second causes,
and then produces the effect by direct fiat.  It is only when
laws fail, that 0 mnipotence acts' directly.  "Whenever there-
fore we trace out these methods of action, we gain a clearer
insight into the character of the great Father: just as we
can see the mind of a fellow man by studying his writ-
ings.   So that by searching out second causes, we  elevate,
rather than lower our ideas of God.
  Premising then  that it is our duty to search for natural
causes to account for  every known event,  and that we are
bound so to account for them when these causes are com-
petent to produce them, I ask you to consider with me,
in the hour allotted us, the Forces of Nature.
   "Whenever we speak of Force, we have a general under-
standing of the meaning conveyed by that term.  But it
is by no means easy to give an exact definition of it.  "We
may say that Force is power; but by this we simply sub- 
4
stitute one word for another.  We may define Force to be
the Divine energy pervading nature; but this, though per-
haps acceptable as  a theological, is not a good physical
definition.
  Let  us  therefore  take a few examples among the best
known forces and see in what their peculiar essence consists.
  Take a rod of glass, for instance, and rub it with a piece
of silk, and at once there is developed, both in the glass
and in the silk, a peculiar power.   By bringing light
bodies in the vicinity of  either the  glass or the silk, they
at first fly toward it,  and are then repelled.   Attraction
and repulsion, or motion, is then a manifestation of  the
Force  we  call Electricity.
  So too if we fit an iron ball accurately into a ring, and
then place the ball in a fire, we shall find that when it has
become hot, it will no longer pass  through the ring.  In
common language it has expanded.   But this expansion is
a motion of particles  from the centre  toward the circum-
ference, effected by the Force we call Heat.
  We  mio;ht continue this  examination and  include  the
other  Forces.  Light is propelled by rapid undulations of
a tenuous ether.  In fact, this very vibration, this motion,
is the real essence of  Light.
  From these examples  we can gather the  definition of
Force  now generally received.  Force is whatever has a
tendency to produce or modify motion.1  Either molecu-
lar, in  which the ultimate atoms of the matter move, or
motion of  the entire mass.  Considering that nothing can
produce motion, but motion itself, many physicists  main-
tain that Force is itself  motion.
  Moreover, Force may act in various  directions and with
varying intensity.  It may affect the  constitution of the
substance  upon which it acts, so altering its  properties

  1 W. R. Grove, Correlation of Physical Forces, 3d ed. p. 16.  Ganot,
Traite" de Physique, Paris, 1859, p. 18. 
5
that it is no longer cognizable:  it may give rise to new
properties  in matter, either temporary or permanent: or
it may temporarily alter some of its previous qualities.
  To illustrate ; a piece of wrought iron is tough, strong,
and malleable.  It has a brilliant lustre, is grey in  color,
and fibrous in texture.  Now if it be exposed for a time
to the action of the weather, it is seized by a giant force,
and converted into rust, which is totally unlike iron.  The
iron has become  brittle, weak, and fragile.  Its color is
red, it has no lustre, and is granular in texture.  The
Force which has changed the metal thus, it is the chemist's
province to study:  he calls it Chemical Affinity.  The
rust he names oxide of iron and says it is no longer a sim-
ple  body like iron.   "Would you doubt the evidence of
power in this Force ?  There is that mighty ship to whose
strength the earth and the forest have contributed.  Those
massive bolts which  hold  her  sides together and enable
her to defy the assaults of the waves may be silently taken
apart and made weaker than a rope of sand by the action
of  this force, resident in the salt  water.   An  iron rod,
which a ton weight can not break even in a single section,
may have every atom separated from its fellow, by a little
weak acid.
  But again: place this bar of iron  in  contact with that
curious substance  lodestone, and immediately it acquires
a new property ; that of attracting to itself other pieces of
iron.  If separated from the lodestone, the power is lost.
If, however, the iron be previously converted into steel,  a
re-arrangement of its particles takes place; and if it be
again  presented to the lodestone,  the  same phenomena
appear but with the difference that they are now permanent.
Here a peculiar force, which we term magnetism, has im-
parted new properties to the metal:  in the one case tempo-
rary, in the other permanent, without affecting any other of
its properties.   If you ask for a proof of its power, see a ton
of iron, hanging1, like the  fabled coffin of Mahomet, un- 
6
 supported, 'twixt heaven and earth, under the influence of
 magnetism, in the experiments of Dr. Page.
   If, lastly, this bar of  iron be thrown into a fire and  the
 heat be urged by means  of air blasts, the solid iron changes
 its physical state and becomes  liquid.   But if allowed to
 become cold again, it returns to its previous solid condi-
 tion.  I have already alluded  to  another change  which
 iron experiences even by very slight variations of temper-
 ature :  namely, its expansion by an  increase of heat.
 Thus an alteration in its relative weight is effected, and
 its specific gravity is lessened.  In both cases we  have a
 temporary change wrought out in some previously exist-
 ing property of the substance.
   Such Forces as those illustrated by the last two examples
 the  physicist claims as  fit subjects for his investigations.
 These it will  be  noticed  do  not  produce  permanent
 change in all  the properties of  a body.   He  therefore
 group^hem together.   He speaks of the Force of Attrac-
 tion ; of Heat;  of Light;  of Electricity; and of Magnet-
 ism, as thus associated.
   These illustrations might  be  multiplied  to any  extent,
 did time permit.  But we pass to notice a theory of some
 value in this connection, though purely hypothetical.
   Speculations  on the  constitution of  matter have been
 offered from the earliest  times.  These hypotheses may be
 represented by that of Sir Isaac Newton, who considered
 matter to be composed of hard impenetrable particles, in-
 capable of further  subdivision.1  Of Bishop  Berkeley, who
 asserted that matter had no objective, but only  a  subjec-
 tive existence.2  And of M. Boscovich, a Prussian philoso-

  1 Opticks p. 375.
  2" The existence of bodies out of  a mind perceiving them, is not only
impossible, and a contradiction in terms; but were it possible and even
real, it were impossible we should ever know it."  Berkeley, quoted by
Dugald Stewart, in his Philosophical Essays, Edinburgh, 1855,  p. 88. 
7
pher, whose ground is intermediate.  He maintains that
matter itself is force.1  Thus if you bring the mind in con-
tact with  any  external object, by the medium of the
Benses, you can  derive no idea of it beyond that which
force produces.   Take a stone for example.  By the eye
you discern  form,  color, roughness or smoothness, &c.
But are not these all  the  result of force resident in that
stone, which causes it so to reflect light to the eye ?  By the
sense  of touch you ascertain its hardness, its temperature,
&c.   But  are not these  all  equally the effect of forces
upon  the senses ?  In short, forces  are competent, either
singly or  in combination, to produce  all the  effects by
which we gain  our knowledge of matter.  May we not
then  accept the hypothesis that matter is but a combina-
tion of the different forces, as at least possible ?  And that
the differences we perceive  in it, are caused by the varying
proportion of these forces present ?   Force is as eternal as
the truths of mathematics.  How sublime then,—and the
more  so  because comprehensible,—in  this view of the
case,  appears the creation  of the  Universe.   When the
great fiat of creation went forth, the Forces came together
by Almighty power and matter  was.  At the  conclusion
of all things how much more  sublime will be the edict

   i"The effects for example, which  are vulgarly ascribed to actual con-
tact, are all produced by repulsive forces occupying those  parts of space
where bodies are perceived by our senses; and therefore the correct idea
that we ought to annex to matter considered as an object of  perception, is
merely that of a power of resistance, sufficient to counteract the compres-
sing power which our physical  strength enables us to exert."—Boscovich,
Theoria Philosophise  Naturalis, Vienna, 1758.
   Upon this, Dugald Stewart remarks in the work just quoted, p. 93 : " It
can  scarcely be denied, that the author or his commentators have been
 successful in establishing three propositions.   I.  That the  supposition of
particles extended and perfectly hard, is  liable to strong, if not to insur-
mountable objections. II.  That there are no facts which afford any direct
evidence in  support of it; and  III. That there are some indisputable facts
which  favor the opposite hypothesis." 
8
which resolves those Forces  again into individuality, and
matter itself shall vanish away.  Thus,

         " The cloud-capped towers, the gorgeous palaces,
          The solemn temples, the great globe itself,
          Yea, all which it inherits, shall dissolve;
          And like an insubstantial pageant, faded,
          Leave not a rack behind."
  Turning now to consider  particularly  some of these
Forces, we will first notice Heat.  This is perhaps the best
known of nature's  Forces.   Man uses it  more  than any
other for the accomplishment of his purposes.  We have
noticed already some of its effects upon matter.   Its pres-
ence constitutes warmth; its absence, cold.   Its manifes-
tations  are marvellously paradoxical.  It  exists in  all
bodies; even the coldest ice contains it, and will impart it
to frozen carbonic  acid.  Not only is this  true, but the
zero or point of absolute cold has never yet  been reached
even  artificially.  Upon  its presence, in  greater  or less
amount, depends  the  condition  of  solidity, fluidity,  or
gaseity; the three great divisions of matter.  By increas-
ing sufficiently the heat, all substances may be converted
into gas; by diminishing it all may become  solid.  More-
over  if by any means we can force a solid to become  a
liquid, or more especially a gas, the heat necessary to  the
existence of the latter is absorbed and cold is produced.
Upon this principle  depend  freezing mixtures.   By  the
affinity of salt for water,  it causes  a  solid  ice to  be-
come liquid;  cold is  the result, and in this way ice cream
is made.  An admirable  adaptation of this principle is
seen in the machines for the  artificial production of  ice.
In  Liverpool, in the  summer of 1860, I  witnessed their
operation.   By an  exhausting pump  worked by a steam
engine  the atmospheric  pressure was removed from  the
surface of ether, confined in a metal cylinder, placed hori-
zontally in a tank of  salt water.   The ether flashed  into 
9
 vapor, taking the heat necessary to its  existence in this
 condition from the surrounding salt water, which was thus
 cooled down to 25° F.   Salt water is used because it does
 not congeal at this low point.   This  water thus  cooled,
 was  then made to circulate round tinned copper boxes,
 containing pure water, which in a few minutes was frozen.
 The salt water in completing its round, gained only 5°
 or 6° of heat,  and was  returned again  to  the tank by a
 pump.  The ether vapor, removed by the exhausting
 pump, was passed through a worm, coiled in a large cistern
 of water, and condensed to be again used.  Thus  by me-
 chanical  means heat is absorbed, cold produced, and ice
 made to the extent of four tons daily.
   Conversely, if by any agency, we can  reduce a gas to a
 liquid, or this to a solid, heat  is evolved.   A familiar
 illustration is  afforded in  the slaking  of lime.   Liquid
 water unites with caustic lime  forming a solid hydrate,
 and a temperature of 570° F. is developed.
   These facts prove that though a thermometer plunged in
 a solid, liquid, or gas, may indicate the same temperature, yet
 that the amount of heat in them is very different.   Beside
 the heat sensible to the thermometer, we have hidden or
 latent heat, which is evolved whenever a change of  state
 from the rarer to the denser condition takes place.  Thus,
 when a ton of water is frozen, sufficient heat is evolved to
 raise another ton  of water from 32®  F. up to  174° F.:
 proving  the paradox so  often stated, that  freezing is a
 warming  process.   When  steam is condensed to a liquid,
 an  enormous quantity of heat  is set free.  In this fact is
 found the applicability of steam for the purpose of heating
 our dwellings.   While water may leave the boiler at 212°,
its boiling point, circulate through the pipes and return,
having lost but 5° or 6° of heat, steam leaving the boiler
at the same temperature, will  return water at the boiling
point, the heat necessary to its vaporous condition, nearly
                 2 
10
1000°, having been  imparted to the  air  of the rooms
through which it was conveyed.
  But Heat is a Force; and the  best evidence of this, is
the expansion which it produces in all bodies.   A bar of
iron one square inch in section is stretched 1-10,000 of its
length by a ton weight.  The same elongation  is effected
by an increase of temperature of 16° F.1  On heating an
iron sphere from 32° to 212° F., Kussne found that its ex-
pansion exerted a force of 4,000  atmospheres upon every
square inch of its surface;  an amount equal to 30,000,000
pounds upon the whole. It is by such expansion that the
rails  upon our railways are frequently torn  up.  From
Liverpool to Manchester, Eng., the rails are 500 feet longer
in summer than in winter.   If therefore allowance is not
made for this expansion, serious accident may be the result.
  But we must pass to the more subtle Force,  Light. Who
of us does  not daily rejoice in the light, and yet who of us
can tell with certainty what it is ? Was Newton right when
he  maintained  the emission theory;  or Huyghens, when
he proposed that of undulations ?  Of its origin we known
only the Divine command,  " Let there be  Light."  As
says Milton ;—

      " ' Let there be Light' said God ; and forthwith Light
         Ethereal, first of all things, quintessence pure,
         Sprung from the deep ; and from her native East
         To journey through the airy gloom began,
         Sphered in a radiant cloud, for yet the sun
         Was not; she in a cloudy tabernacle
         Sojourned the while. God saw the  Light was  good,
         And light from darkness by the hemisphere
         Divided; light the day, and darkness night
         He named."

  From our  great central orb  then,  comes this Force.
Thrown on nature and a thousand  delightful forms  start
  1 W. A. Miller, Chemical Physics, p. 178. 
                          11

up as if by magic.   Without Light what is the delicate
blush of  the  rose or the magnificence of the landscape ?
What  Michael Angelo's triumphs in sculpture or the ex-
quisite coloring of a Raphael or Titian ?   From its  home
ninety-five millions of miles away, this beneficent  agent
comes forth to bless  and to gladden mankind.  Pure and
white as the heavens from which it issues, it carries in its
bosom all the colors and shades of earth.  Moving at  a
velocity of nearly two hundred thousand miles in a second
of time, it is jet composed of rays, undulating with vari-
ous rapidities.  Each ray is a color.  Red, orange, yellow,
green, blue,  indigo, violet  is the  order  in  which  they
vibrate.   While of red waves there are forty thousand in
a single inch, of blue there are sixty thousand.  As in two
hundred thousand miles there are twelve thousand million
of inches, and as this distance is passed over in one second,
it follows that of red, there are four hundred and eighty
million million, and of blue, seven hundred and twenty
million million  vibrations in a second of time.  To see a
source of light for one second requires the entrance of all
these vibrations through the pupil.  To see a red object,
four hundred and eighty million million of waves  must
break upon the retina and throw it into vibrations as rapid
as this.  To see a blue, the retina must vibrate seven hun-
dred and twenty million million  times between  two ticks
of a common clock.
  But how shall we demonstrate this omnicolored charac-
ter of the light ray ?  If we pass a beam of white  light
through a prism, we find that on emerging it is composed
of a series of colored  bands, parallel to the axis of the
prism, in the order already mentioned.  This is called the
Solar  Spectrum, and it is due to the  different degrees in
which the different colors are refracted.  Red is least bent,
so it is  found in nearly a right  line with the  original
beam: violet is  the  most bent,  so  it is farthest removed 
12
 from that line.  If instead of white light, we pass light of
 one color through the prism, we have a spectrum consist-
 ing of a single band of the same color.  If there be more
 than one color we have bands, numerous according to the
 complexity.  With purple light, for example, we should
 have a red and a blue band, widely separated.  Thus the
 color, as well as the position of the bands, determines the
 identity of the colored rays.  Certain chemical substanc.es
 color flames.  If  these colors are analysed  by the prism
 they give spectra more or less complex, but all distinctive of
 the substance used.  We may then determine the charac-
 ter of a substance,  by examining  its flame  with a prism.
 By the color and position of the bands given by the purple
 light  above mentioned, we determine that  potassa  gave
 the color to the flame.  This is Prof. Bunsen's new method
 of chemical analysis.1
  But beside  the  colored  bands  of the  solar  spectrum,
 there are other and dark bands.  Fraunhofer investigated
 them and  named  them by the letters of  the  alphabet.
 One of the most  prominent of these  lies in the brightest
 portion of the yellow band.  It is called Fraunhofer's line
 D.  Now a flame  colored by sodium gives a yellow band
 precisely in the same position.  Can we make this yellow
 line dark ?   By placing a strong white light, as that of the
 electric  arc, behind the yellow flame, there  is a spectrum
 produced, in which this yellow band is replaced by a  dark
 one.  The  yellow flame has absorbed all the yellow  from
the white  light  behind it;  the space which  this color
occupies  in the  spectrum is therefore dark.  This is the
 great discovery of Kirchhoff'.   It is,  to use his own words,
the fact that " a flame absorbs rays of the same refrangi-
bility as those which it emits."2   Upon this  discovery
  1 Poggendorff's Annalen. Bd., ex, 1860.
  * Researches on the Solar Spectrum, #c.  Translated by Roscoe, London,
 1862, p. 14. 
13
Kirchhoff originated one of the most brilliant generaliza-
tions ever recorded in science.  If, said he, we can pro-
duce the dark band D, by placing an intense light behind
a sodium flame, is not that line in the  solar spectrum so
produced?  In  other words, is not the sun a solid body,
intensely luminous, surrounded  by an  atmosphere of the
substances composing it, in vapor, one of which is sodium?
Other dark lines were compared in this way, and he ascer-
tained the identity of solar bands with  those produced by
the  metals calcium, magnesium,  barium,  iron,  nickel,
copper, chromium, and zinc.   These metals exist therefore
in the sun.1  The light of the stars has also been subjected
to the same rigid analysis.   Their composition varies from
that of the sun, and they differ among themselves.2  So
from our little planet does the chemist, standing side by side
with the astronomer, reach out his hand to grasp  these
distant orbs, and to analyse them by that light which has
been tens and perhaps thousands of years on its way to re-
veal its secret.
   But has the light of our sun no other mysteries ?  Has it
no other qualities than those mentioned ? It gives us light:
does it do no  more ?  Witness that  curious, that almost
magic art, by which in a second of time, the shell bursting
in the air, the crowded thoroughfare, with its whirl of life,
 or the  lineaments of the human  face  may be accurately
 transferred to paper.  From whence comes the power to
 effect this ? In the light which comes to us from our sun, we
find not only rays giving light, but also chemical or actinic
 rays, and heat or calorific  rays.   In  the  spectrum the
 maximum of heat, when a glass prism is  used, is in the
 red ; of light in the yellow ; and of chemical power in the
 violet.   We can therefore isolate each  of these by screens

   iKirchhoff, Op. Cit., pp. 20, 21.  Also Phil. Mag., Aug., 1860.
   *L. M. Rutherfurd, Sill. Am. Jour., 2d series, vol. xxxv, p. 71. 
14
of colored glass.   By means of glass colored yellow with
the oxide of silver, we can cut off both the actinic and the
calorific rays, while the intensity of the  light rays is but
slightly diminished.  If we use a glass colored blue with
oxide of cobalt, the actinic rays freely pass while the heat
and light rays are stopped.   Lastly, if  a red  glass colored
by suboxide of copper be used, the heat rays permeate it
freely, while no passage is afforded to the actinic rays, and
only a feeble light is transmitted.  It is a well known fact
that a photograph can be taken with as much facility in a
room whose windows are of deep blue glass, even though
to ordinary appearance it be entirely dark, as in one open
to the full light of day.  This principle of screening off the
rays is of great practical value to the horticulturist.  Seeds
in  germinating  need chemical power  to  convert their
starch into sugar.  When therefore  the florist  wishes to
force  his seeds,  he covers them with a dark blue glass.
As they advance in maturity, they need  light rather than
actinism.1   The  blue glass is therefore removed, the  yel-
low substituted and the vigor of growth continues.  When
the time of fruiting  comes, heat becomes more essential.
A red glass takes the place of the  yellow  with equally
good  results.   Thus  by following the needs of  the plant,
he is  successful.   Had  he  used the  colors inopportunely
the plant must have perished.
   This composition of sunlight is therefore for a benefi-
cent purpose.   Mark now its beautiful  adaptation to the
varying condition of vegetation.  If you ask the practical
operator, he will tell  you that the best season of the year

  1 "It was long a question whether the decomposition of carbonic acid
by plants was due to the luminous or to the chemical rays.  It is now clearly
established that the luminous rays are the most active in producing this
effect;  which they do indirectly by exciting the vital powers of the organ-
ized structure."
  Poetry of Science, by Robert Hunt. London, H.  G. Bonn, 1852, p. 182. 
15
for photography is the spring.  When all the rich green
of our fields is yet unfolded from the embryo, then it is
that a large excess of actinic power is concentrated in the
light of the sun.  But vegetation advances and what just
now was the germ has become the plant.  Increased light
is necessary to continue its growth, and lo, the sun beams
forth with a  brighter glow and it is accomplished. Au-
tumn advances upon  summer,  and  the  object  of the
plant's existence is yet to be attained.  It is to yield seed
to reproduce  its kind.   To ripen  this fruit, to perfect
this seed, increased heat is essential.   And again the sun
adapts itself and furnishes it.  Relatively to the light and
chemical power, the heat is at a maximum in the fall of
the year.   Can we have better evidence than this of de-
sign in nature ?x
   But another of these subtle agencies awaits our notice.
It is Electricity.  See the ancient philosopher of Greece
 as he rubs the little piece  of riksxrpov, presents it to bits
 of pith, and notices  how they are attracted.  Watch the
 peculiar satisfaction with which this singular property was
 ascribed to the agency of minute insects, which threw out
 invisible tentacles or claws and drew up the pith.  But the
 world slept on for twenty centuries, while this wonderful
 agent lay unborn.  Then behold it touched into life  in
 England;  see its rapid strides of progress,  passing at  a
 bound from the cradle to manhood.   Gradually its inner-
 most secrets are brought to the light of day and applied
 for the good of man.  Mankind  honor Franklin equally
 because  "Eripuit ccelo  fulmen," as well as "sceptrum
 tyrannis."  Who, standing by that great philospher, could
 have comprehended  the vast benefit to the world of that
 kite experiment, when he led the lightning captive on the
 string and drew it harmlessly from the key ?  Now every
 house may rear its gilded point to the skies; and. as the
   i Robert Hunt. Op. Cit., p. 374, et seq. 
16
lightning's  venom is withdrawn, fear passes and all is
safety and  happiness.   But the eighteenth  century is
drawing to its close and a professor of anatomy at Bologna
is busy in his laboratory, striving to ascertain the nature
of that vital force with which organic beings are endowed.
Instead of this, however, he stumbled upon a fact which in
its practical bearings was of far more importance.  Blind,
save  to  his  one cherished idea, he would not see the
prize within his grasp.  It was reserved for his talented
pupil and nephew to develop  it into a science.   And from
Volta's pile, as an ancestor, how numerous are the pos-
terity.  The methods of generating this  peculiar power
are almost infinitely varied to answer their numerous ap-
plications.  And  to-day, as  a direct  gift from  Yolta,
Maine can  converse  with California, " as a man talketh
with his  friend."   To the development of this wonderful
force, we owe a thousand of earth's blessings.  The arts
of mining and metallurgy, of civil  engineering and  of
military  tactics, out of hosts of others, claim its  daily
assistance.  And as it comes forth, crowned already with
laurels, to take its place among the sciences, it has a con-
sciousness of power, which though yet latent, is destined
to achieve still greater results for humanity.
  Let us notice some facts  concerning  this power which
have already been revealed.   The electricity of the  thun-
der cloud carries power as does the English locomotive,
small in amount but of enormously high pressure.   While
that of the telegraph seems  more like the energy of the
Great Eastern,  of low pressure, yet vast in amount.  It is
evident  that an equal amount of work may be done  by
water whether it falls  in  a  small stream from a great
elevation, or rushes in a mighty torrent over a dam but a
few feet  in  height.  In the former case we illustrate the
electricity of friction.  In the latter that of chemical action.
The former  moves at the astounding velocity of two him- 
17
dred and  eighty-eight thousand miles in a second.1  The
latter more slowly, being as low as eleven thousand miles.2
The distance through the air which the spark will traverse,
depends  upon  the  pressure  or  tension.   The magnetic
effect of this agent, on the contrary, has reference to the
amount  of Electricity which circulates.  The  Electricity
which is excited by rubbing a glass tube with a silk hand-
kerchief,  will easily pass  across  half  an  inch of  space;
while the great voltaic battery of Mr. Children, consisting
of twelve hundred and fifty pairs of plates, was unable to
project  a spark one-fiftieth  of  an  inch  through  space.3
But on the other hand, a piece of copper and of  zinc,
the size of  a cent, will produce a magnetic effect far be-
yond that which is given  by the most powerful discharge
of frictional electricity ever obtained.   Mr. Whitehouse, in
experimenting  upon the  Atlantic  cable,  sent a message
through one thousand miles of  it,  submerged, with the
power generated by a voltaic element consisting of a silver
wire and  a zinc wire the size of a pin, excited by a drop of
acid, supported between  them by  capillary action.4  The
electricity of friction is therefore characterized by its in*-
tensity, and that of chemical action by its quantity.
   We  have called electricity a force.  Let us hear the
greatest living philosopher, Mr.  Faraday,  upon this point.
" The quantity of electricity," says  he, "required to de-
compose  one grain  of water is equal to eight hundred
thousand discharges  of  an  electrical battery, exposing
thirty-five hundred square inches of surface, charged with
thirty turns of a powerful  electrical machine."5 That is, to
decompose  one grain of water requires the electricity from
a charged surface of four  hundred acres, which amount is
  i Wheatstone, Phil. Trans., 1834, p. 589.
  2 Silliman's Physics, 2d edit., p. 538.
  3 Gmelin's Chemistry, Vol. i, p.  418.
  * Chambers' Journal, 2d series, Vol. vin, p. 122.
  5 Faraday, Experimental Researches in Electricity, Vol. I, p. 253.
                  3 
                          18  '

scarcely exceeded in the heaviest thunder storm.   If this
were spread upon a cloud two-thirds of a mile distant from
the earth, it would exert an attractive force of sixteen hun-
dred and  sixty-four  tons !  If we could  attach the atoms
of oxygen in this grain of water to one thread one twenty-
fifth of an inch long, and those of hydrogen to another,
the force  required  to  separate the threads in one second
of time would be 7,250 tons!  Yet this  is easily  accom-
plished on the lecture table.
   Closely connected with this is  another force to  which
we must  refer briefly.  I allude to magnetism.  In the
town of Magnesia, in the province of Lydia, Asia Minor,
is a black ferruginous mineral, which, from remote anti-
quity, has been known to possess the property of attracting
to itself small bits of iron.  From the locality where the
mineral was discovered the property gets its name, mag-
netism.   In  our own northwest, large  beds  of this ore
seriously interfere with the ordinary methods of land sur-
veying.  If this ore be rubbed  upon a steel needle, we
find that the  property is communicable, and that if the
jieedle,  now  a magnet, be carefully laid upon the surface
of water, it will arrange itself in a direction nearly parallel
with the  axis of the earth.  Moreover  we find that the
end of the needle toward the  north pole of the earth is
repelled by the same end of another needle similarly pre-
pared, while it is attracted by its opposite end.  We  con-
clude then that the earth is a great magnet.  Proceeding
upon this supposition, M. Gauss has calculated  that the
magnetism of the  earth  is such as would result from the
existence  of  six  magnetized  steel bars, weighing one
pound each, in every cubic yard  of  its  mass.  Compared
with one such  magnet, the earth's magnetism is repre-
sented  by S^^OOO^OO^OO^OO^OO^OO.1  There is evi-
dence of power  in the amount which a steel magnet made
   1 Prof. Faraday, Annual of Scientific Discovery, 1852, p. 111. 
19
in the manner indicated would sustain.  Sir Isaac Newton
wore in his finger-ring a piece of lodestone which, though
its weight was only three grains, was yet able to lift seven
hundred and sixty grains.1   Ordinarily steel magnets  can
not in this manner be made to sustain more than twenty-
eight or thirty times their own weight,
   There is  still another force inviting  our examination
which, in the extent of its range of action, or in the won-
derful results which it produces, is not surpassed by either
of those already considered.  This force  is chemical affin-
ity.   What  more  mysterious than those  transmutations
which it effects ?  What more  paradoxical than  many of
its  facts ?  Yet  to its unceasing energy we owe our exist-
ence ; even the world about us was formed by  this  force,
and is  now  held  together by it.  What its essence is we
can not say, but its effects we daily witness.  Even  in the
very constitution of matter we detect it.  The pure  water,
so  essential  to  life, whether taken from the frozen north
or the parched tropic, shows by its uniform eight parts of
oxygen  to one  of hydrogen, that one single force  orders
its formation.  Every mineral, every plant, every animal
has its components brought together and united by  chem-
ical  affinity.  But it is when this force brings  about a
change  in matter  that the  results are most stupendous.
See  the people  of Lisbon  rushing frantically  from their
tottering houses to be slain by falling timbers and  stones*
in the streets, during the great earthquake of 1755,  if you
would understand  the power of chemical action.  Witness
Vesuvius putting herself in martial array and hurling fiery
lavas from  her  arsenal to  overwhelm Herculaneum, or
clouds of cinders and scoria to cover the city of Pompeii,
if you would comprehend its energy.   But the cause of
these changes is none the  less  powerful because  silent.
Working thus  quietly it achieves its noblest  triumphs.
Consider the fern  forests of the carboniferous age.  See
  1 Silliman's Physics, 2d ed., p. 530. 
20
that rank vegetation covering half our  continent, soon to
be overwhelmed in one of those vast cataclysms of nature,
and covered with sand and gravel.  Now chemical  force
lays hold of the woody fibre and, at the depth to which it
is buried, converts it into coal.  How vast this  action was
appears from the fact that, were the  present consumption
of the world to be quadrupled, and the enormous amount
of four hundred million tons of  coal  used annually, the
amount of this material  in our own country would supply
the demand for ten thousand years.   And yet  this action
was silent and gradual.
  But, again, how has chemical force enriched mankind!
Every day brings numberless blessings which  this agent
has conferred.   The light  which streams upon us as we
wake  in  the morning passes  through glass made  by a
chemical  process. The  linen with which we  clothe  our-
selves  has  been bleached  by it.   The bread upon our
breakfast table depends on chemical  force for its light-
ness.   Our improved  stoves are made as its  laws  have
dictated.   The morning paper  has come to us from pulp
which it has whitened, and  with characters printed with
ink of its  suggestion.  The elegant colors which we use
to decorate our houses and  our persons it has  unfolded.
The dazzling  Florence white of the inside paint recipro-
cates its effect with the brilliant hues  of the wall paper.
The magenta,  mauve, roseine, azuline and bleu  de  Paris
of our silks have been called forth by its magic  wand from
coal tar, only to  look  upon the Berlin blue, ultra marine
and carmine of the artist,  from  a  scarcely less ignoble
origin.  The delicate flavors of the table, as well as the
perfumes of the toilet, have been evolved under its direc-
tion.   In every department of household economy,  alike
in the drawing-room  and in the kitchen, its assistance is
invoked.   It has carried man on in  civilization, and civil-
ization has in turn sustained its labors, until man has well
nigh attained the summit of perfection. 
21
  Turn we  now to consider a little more fully the nature
and origin of force.  If I were to state that matter  is in-
destructible, I should utter a simple truism which is fami-
liar to  every one  before  me.    Though protean in its
appearance, matter ever  remains the  same in  essence.
Indeed since the creation  of the  earth not one particle of
matter, if we except aerolites, has been added to or taken
from its mass.  The fuel we burn in our stoves passes up
the chimney as invisible gas, but carries with it the entire
weight of the material consumed.   If a piece of gun
cotton be placed  in a globe previously exhausted and
weighed, on flashing it by means of electricity there will
be no change  in  its weight.  Though by the action of
chemical force matter may disappear and may seem to be
destroyed, yet by this same  force we  can  cause it  to
reappear with all  its original characters.  But that force
is subject to the same  law; that  force is never lost; and
that the  store of force  in our universe  is  the exact
equivalent of that which  it contained when it was first
ushered into existence,  these are facts  not as commonly
accepted.   Can we not then annihilate force ?  I reply no,
no more than we can matter.  A house may be destroyed
by fire, but not the matter of which  it  is composed.  So
the form in which the force appears may be changed, but
the force itself reappears in some other  form and  as truly
exists  as  before.   We  can make the statement more ap-
parent by a few illustrations, and we will use mechanical
force  or motion as  the starting point, because with it we
are best acquainted.  If a blow be struck upon an anvil
by a  hammer, the  force  of the blow is received by the
anvil and appears lost.  If a rifle  ball  be projected against
a rock, its force is  spent apparently without effect.  If a
stone fall  from a  height, it strikes the  earth and its force
seems annihilated.  Now can we trust the first appearance
in these cases ?  By no  means.   By careful scrutiny we 
22
shall discover that the force which  seems lost  has only
changed its state.  It is  indeed lost as motion but it ap-
pears as heat.   The blacksmith by continuing  his  blows
soon  makes the iron hot.  And if  the rifle ball be care-
fully examined it will show signs  of fusion.  But not only
can we make these statements in general terms, but we
can estimate the relation with mathematical precision.   If
we allow a leaden ball to  fall from a height of twenty-six
feet to the earth, its motion will be stopped and converted
into  heat,  which,  were it all  concentrated  in  the ball,
would raise its temperature one degree, Fahrenheit.1  The
force with which a body strikes the  earth depends upon
the height from which it falls.   The height to which a
body rises, when thrown upwards, is as the square of its
velocity.  Therefore  the  force with  which it strikes, and
the consequent heat  generated, is as the square  of the
velocity.  The same  principles hold true if we use gun-
powder  as the  moving force.  Hence it follows that if we
double the velocity of a projectile we increase  the heat
generated, when its  motion is arrested, fourfold.  If we
treble its velocity we  augment the heat ninefold,  and  so
on.  Now  if the rifle ball just referred to fell by gravity
through 772 feet, its velocity would  be  223 feet per se-
cond.  If this motion were suddenly arrested, and all the
heat were collected in the lead, its temperature would  be
elevated thirty degrees, Fahrenheit.  But when thrown  by
gunpowder six times this velocity, or 1,338 feet a second,
would not be inordinate.  With six times the velocity,
62 or thirty-six times the  amount   of  heat, or 1,080°,
Fahrenheit, would be generated.  Were  this  heat all  re-
tained in the  bullet  it would be far more than sufficient
to fuse the lead.  If a ball of iron be used,  the tempera-
ture to which  it will  be raised is only one-third of this,

  1 Prof.  John Tyndall, Heat considered as a mode of motion, Am. edition,
p. 55.                                  J      '         ' 
23
because its capacity for heat is greater in this ratio.1 Still,
in the experiments with the  Whitworth gun in England,
a bright flash of light appeared when the hexagonal eighty
pound bolt struck the iron target, as if a gun had been
fired in return ; and the bolt  when found in the  interior
was too hot to handle.
  What  we have now shown to be true of falling bodies
and of projectiles, is true of mechanical  action of any sort,
and with the same result.  The attendant neglects to oil
the axle bearings of our  railway  cars.  Presently they
begin to  smoke, the train lags, and soon after the car is in
flames.   That force, which, suitably applied would have
hurried the train onward, is lost by friction and converted
into  heat.  Count Rumford  caused a cannon to revolve
against a blunt borer, the whole being immersed in water.
In two  and a half hours the water boiled.2  This is also
true of compression.  A  piece of  wood  suddenly and
strongly  compressed in the jaws of a vice becomes hot.
And I need hardly refer you  to the familiar experiment
with the fire syringe to  prove  the  same  principle.   In all
the cases adduced, we have mechanical force apparently
lost but really converted into  heat.  And the one is  the
exact equivalent of the other.
  Now what is true of mechanical force, is true of all other
kinds of force.  All of these Forces of nature are thus
transmutable.  Suspend their manifestation in one direc-
tion, lo !  it appears in corresponding quantity in another.
We cannot extinguish force.   Whatever form it assumes,
it is only one of many in which it may show  itself: And
if this be true, it is also true that no force can be lost.  In
one form or another, the force of the universe is preserved
to undergo transmutations  to the end of time.
  In the  light of the statements  which have thus far been
1 Ibid, p. 56.
2Phil. Trans., 1798, p. 80. 
24
made, how different do the forces which we have consid-
ered appear?   Let us notice them now in their relation to
each other, viewed from our  new standpoint.  We have
seen that mechanical force as motion, is, when arrested,
converted into heat.  This leads us to  inquire,  what is
heat ?  Is it material, as the older philosophers considered
it ?   Or is it merely a property of matter and itself  im-
material ?  This was answered by Sir Humphrey Davy, in
his  first scientific memoir, as follows :—By the friction of
two pieces of  ice  against each other at a temperature  be-
low the freezing point, these were melted.  As the capacity
of water for heat is greater than that of ice, the heat pro-
duced did not  come from the water obtained, by virtue of
a diminished  capacity.  Of course in the case of ice, it
could not have come from  oxidation.  By producing fric-
tion in a vacuum, he demonstrated that the heat of fluidity
did not come from the ice nor from surrounding bodies by
conduction.  But if heat  be material, these are all  the
ways possible by which the water could have obtained it.
Now the heat  of friction may be produced to infinity.  In
view of these  facts, he says, " It is evident that caloric, or
the matter of heat, does not exist."1  We come to the other
theory therefore and, for reasons already implied in speak-
ing of the conversion of motion into heat, conclude that
heat itself is motion.  When a ball falls through the air
and produces  heat by its  sudden stop, that  which  was
motion of the  mass has become motion of the molecules,
or  in other words, heat.  Heat is therefore molecular
motion, a property of matter rather than matter itself.
Hence it is easy to see how the intensity of motion deter-
mines the intensity of the heat produced.  And  also the
converse of this proposition: that molecular motion  may
be  reconverted into mass motion.  Mr.  Joule of Man-
chester, England, has been  experimenting since 1843 to
  1 Works of Sir Humphrey Davy, Vol. n. 
25
determine practically the ratio of heat to  work; and by
causing paddles to revolve in water,  oil, or mercury, by
the descent of known weights, as well as by other means,
he concludes that a weight of 772 pounds falling through
one foot, produces sufficient heat to raise one pound of
water one degree F.  The term " foot pound," is used to
indicate the lifting of one pound one foot high.  772 foot
pounds, therefore, is the mechanical equivalent of heat.1
This constant may be applied to the solution of many in-
teresting  problems.   "Whenever work is done by heat,
heat disappears.  A gun that fires a ball is less heated than
one that fires a blank-cartridge," says  Mr.  Tyndall.   The
statement that heat may be reconverted into mechanical
force receives its exemplification in every steam engine.
   In these facts we have important examples of what Mr.
Grove calls the " Correlation of Forces," meaning by this
term their  mutual convertibility.   Let us therefore go a
step farther and see how far the forces we have spoken of
are convertible into each other.  Starting with mechanical
force, we  have seen in  every case that it may be converted
into its equivalent of heat.  The same is true of the force
we call Chemical affinity.  When carbon combines with
oxygen, we have heat developed.  And this development
is the same in kind with that  produced by the fall of a
body to the earth ; but in  the one case we have collision
of  sensible masses, in  the  other of atoms.  "Could we
measure the velocity of the atoms when they clash ;  could
we find their number and weight, multiplying the weight
of each by the square of its velocity and adding all together,
we should get a number representing the exact amount of
heat developed by the  union of the Oxygen and the Car-
bon."2  Hence the production of heat  by chemical action

  i J. P. Joule, Phil. Trans., 1850, p. 61.
  2 John Tyndall, Lecture on Force, delivered June 6, 1862, at the Royal
Institution.
                 4 
26
must be regarded as simply a change  in the direction and
character of atomic motion.  The amount of heat developed
in this way we are  accustomed to consider  enormous,
simply because it is most familiar to us.  But  it does not
equal that produced by arrested mechanical force.  " One
pound of  coal in combining  with oxygen,  produces  an
amount of heat which, applied mechanically, would raise
a weight of one hundred pounds to a height twenty miles
above the  earth.   Conversely one hundred pounds falling
from a height of twenty miles and striking against the
earth, would generate  an amount  of  heat equal to that
developed by the  combustion of a pound of coal."1 But
from the data we have, we can compare on a larger scale,
combustion and mechanical force as heat producers.  Our
earth moves 68,040 miles an  hour in  her orbit.   If this
motion should suddenly be stopped, sufficient  heat would
be developed, according to Mayer and Helmholtz, to raise
a globe of lead the same size, 384,000° C. or 691,200° F.
This would not only reduce our entire  earth to fusion, but
dissipate it for the greater part in vapor.  This amount of
heat would require for its development the combustion of
fourteen globes of solid coal, each equal to the earth  in
size.  If now, as would necessarily be the case, the earth
should fall into the sun, the heat developed would equal
that produced by the combustion of sixty-four hundred and
thirty-five worlds  of solid carbon !
  But perhaps the most striking  exemplification of the
power produced by chemical action, through the medium
of heat, is to be found in the various stages of the existence
of water.  Premising that Count Rumford determined that
one pound of hydrogen in combining with eight pounds of
oxygen to form  water, evolved sufficient  heat to raise
34,000 pounds of water 1° C, I go on to quote Mr. Tyndall.
"First, we have  the  constituents of water as free atoms,
1 J. Tyndall, Lecture on Force. 
27
which attract each other, fall, and clash together.  The
mechanical  value of this atomic act is easily determined ;
knowing the number of foot pounds corresponding to the
heating of 1 lb. of water 1° C, we can readily calculate the
number of foot pounds equivalent to the heating of 34,000
lbs.  of water 1° C.  Multiplying the latter number by
1,390 (the number of foot pounds corresponding to 1° C.)
we find that the concussion of our one pound of hydrogen
with eight pounds of oxygen is equal in mechanical value,
to the raising of 47 million pounds 1 foot high !  * * * *
After  combination the substance is in  a state of vapor,
which sinks to 212°, and afterwards condenses to water.
In the first  instance, the atoms fell  together to form the
compound; in the next instance, the molecules  of the
compound fall together to form a liquid.   The mechanical
value of this  act is also easily calculated: 9 lbs. of steam
in falling to water, generate an amount of heat sufficient
to raise 967  x9=8703 lbs. of water 1° F.   Multiplying this
number  by 772, we have  a product of 6,718,716  foot
pounds as the mechanical value of the mere act of con-
densation !   The next great fall of our 9 lbs. of water is
from the state of liquid to that of ice, and the mechanical
value pf this act  is equal to 993,564 foot pounds.   Thus
our  9 lbs. of water, in its origin and progress falls down
three great  precipices: the first fall  is equivalent  to the
descent of a ton weight urged by gravity down a precipice
22,320 ft. high; the second  fall is equal to that of a ton
down a precipice 2,900 ft. high ; and the third is equal to
the  descent of a ton  down a precipice  433 feet high.  I
have seen the wild stone avalanches of the  Alps, which
smoke and thunder down the declivities with a vehemence
almost sufficient to stun the observer.  I have also  seen
snow flakes  descending so softly as not to hurt the  fragile
spangles of  which they were composed; yet, to produce
from aqueous vapor, a quantity of  that tender material 
28
which a child could carry, demands an exertion of energy
competent to gather up the shattered blocks of the largest
stone avalanche I have ever seen, and pitch them to twice
the height from which they fell."1
  To return to our Forces.  Light, also, may be converted
into Heat.   In the view of many distinguished philoso-
phers, none of the sun's direct heat reaches the earth.  As
both light and radiant heat are the same in essence, being
vibrations, it is maintained that if these vibrations rise to
the enormous  rapidity already mentioned, they are com-
petent to affect the optic nerve and produce the sensation
of light.  If they are less than this  they affect only the
nerves of general sensation and produce the impression of
heat. Now, light waves may be so reduced in the rapidity
of their vibrations by passing through certain media, that
they become heat  waves.   Dr.  Franklin long ago placed
pieces of the same kind of cloth, but of different colors,
upon the snow and watched the order in which they melted
the snow beneath them.   He found that this order was
precisely that in which they absorbed the light.   Black
destroys all light waves.  But  it is thereby heated and is
found deepest in the  snow.  Next came blue, green, pur-
ple, red, and yellow.  White reflecting all the lighj rays,
remained on the surface.2   On the other hand, it is main-
tained that the heat from luminous bodies is of two kinds :
luminous  heat rays,  and obscure heat rays.  That the
former alone accompany the sunlight across space and are
converted into obscure rays by absorption in our atmo-
sphere  and on  the earth's surface.   These obscure rays
can not then pass back again and are retained.  As many
of the heat  rays from a bright  coal  fire, being luminous,
pass through a glass screen,  while those from  a steam

  i J„Tyndall on Heat, $c, Am.  Ed., pp. 163,  164.
  2 Cooke's Chemical Physics, p. 653. 
29
radiator, being obscure, are entirely intercepted:  so  the
atmosphere, by allowing the rays of light, according to one
theory or luminous heat rays, according to  the other, to
pass freely through it, while it intercepts the obscure heat
rays, into which  the former are converted by absorption
on the earth's surface,  acts like a mantle to our globe,
protecting it against the intense cold of the celestial spaces
through which we are so rapidly whirling.
   Conversely, we have only to  intensify the vibrations of
the  rays of heat to produce  light.  This we can do by
exposing a piece of platinum wire to a source of heat,
gradually  increasing in intensity.  At  first only obscure
heat rays  are radiated.  Then  the  deepest  red becomes
visible, the very color whose vibrations  are  slowest.  As
the  heat increases orange appears, then yellow, until a
full  white heat  is reached.  And  if this be intensified a
distinct blue can be seen.1  This experiment strengthens
our  conviction that the waves of heat and light differ from
each other only in intensity.
   Electricity may be converted into heat.  This is effected
precisely as  in the case of light,  by lessening the vibra-
tions.   Whenever we cause electricity to traverse  a poor
conductor heat is evolved.  In the case of lightning it is
not  when the electricity passes along the metallic conduc-
tor that any danger is apprehended.  If this conductor be
continuous and  large  enough,  we  may sit  with  perfect
safety   upon a  barrel  of gunpowder  through which  it
passes, during a thunderstorm.  It is  when the rod  is
broken, and the lightning is  caused to pass through a
poor conductor, air, that it is converted into  its equivalent
of heat.  Any combustible in the vicinity of the spark is
inflamed.  A common  lecture experiment is the firing  of
gunpowder by the  spark.  This  can only be effected by
interposing an imperfect conductor, as a wet string, in

  1 Prof. Bunsen, quoted in Brande $ Taylor's Chemistry, p. 97, Am. ed. 
30
the circuit.   The  string lessens by its resistance the rapi-
dity of the waves, lowering them to heat.   The tension of
voltaic electricity being low it  can not pass through air.
Its  heating  effect  is produced when a wire of platinum,
the metal offering most resistance, is placed in the circuit.
In this way submarine blasting  is effected.  The fine pla-
tinum  wire  between  the electrodes is immersed in the
powder.   When it becomes red hot this is  exploded.
  Conversely, heat  may be  converted  into electricity.
Prof.  Seebeck, of the  University of  Berlin, first deve-
loped this fact.  If an iron poker be placed in the fire, a
passage of heat from the hot to the cool end takes place.
But at the same time a  current  of electricity flows in the
other direction.  If two bars of  different metals be sol-
dered together at one end, and the junction be  heated, a
current of electricity is set in  motion from one to the
other.   Bars  of  bismuth  and  antimony  give  the best
effect.   If the electricity be measured by  a delicate gal-
vanometer,  we have an apparatus for indicating slight
variations in temperature far  superior to any other.   By
its  means Prof. Melloni made his masterly researches  on
heat.   He was even able to determine the  relative heat of
insects.
  Magnetism may be converted into heat.  A flat disc of
copper, caused to rotate between the poles  of a  powerful
magnet, speedily becomes hot.   Fusible  metal may thus
be melted.1
  If a bar of  iron, placed  as  the  armature of a powerful
electro-magnet, be rapidly magnetised and demagnetised
by charging repeatedly the magnet, which is  kept cool
by a current of water, its temperature will be raised.2

  1 J. P. Joule, Phil. Mag., 1843, pp. 355 and 439; also Tyndall on Heat,
p. 51.
  2 W. R. Grove, Correlation Physical Forces, p. 159. 
31
  Electricity may be converted into light.  If the elec-
trical vibrations which produce heat are sufficiently exalted
they produce light.  When a spark passes through space
it is luminous.  If the  electrodes of a powerful voltaic
series terminate in carbon points, and these after being in
contact are slightly separated, even in a vacuum, the pas-
sage of the electricity announces itself by the most intense
light which art can produce.  If ninety-two carbon ele-
ments be  arranged in two  series of forty-six  each, the
light emitted is equal to that of 1,144 candles,  according
to  M. Despretz.  It is  to the light of the sun as 1 to 2J.
On the evening of the last Fourth of July, a light of this
sort,  produced by 250  couples,  was projected  from the
cupola of the State House in Boston  in presence of Profs.
Cooke, and W. B. Rogers, which the latter calculated was
equal to that of ten thousand candles.
   Electricity may develop electricity.  If near a wire con-
veying a current of electricity, and parallel but not  in
contact with it a second wire be placed, the ends of which
are connected  with a galvanometer, it will be noticed that
whenever the circuit is* broken or closed the galvanometer
needle is deflected by the passage of a current in  the se-
cond wire.  This  principle, discovered by  Mr. Faraday,
has been  expanded  by Prof.  Henry, who  has obtained
currents of the ninth order, eight of which were entirely
independent of the  battery.  Moreover by varying the
size of the second wire we may obtain in it either a quan-
tity or intensity current at pleasure.
   Electricity may produce magnetism.   Prof. Oersted, of
Copenhagen,  observed that when a wire connecting the
terminals of a  battery was placed parallel to a  magnetic
needle, the needle instantly moved from its position and
attempted to place itself at right angles  to the wire.  If a
piece of iron rod be placed in the latter position it became 
32
magnetic.  This effect is increased  by coiling the wire
round the rod, because in this  case every coil is nearly at
right angles to the rod, and every coil acids to  the result.
Such magnets are called electro-magnets, and they have
been made of enormous  power, capable of sustaining  a
ton  and  more.  But  not only does the iron become  a
magnet: the coil also acquires the property.  If the  bar
be partially withdrawn and then released, it flies back
into  the  centre  of the coil.   Mrs. Somerville, who first
noticed this fact, suspended a sewing needle in the centre
of a  coil without visible support.  This has been named
the axial  magnetic force, and at present affords the only
means of applying this  agent mechanically.  Dr. Page
ran a train of three passenger  cars from Washington to
Bladensburg some years since by the application of this
force,  attaining  a speed of nineteen  miles  per hour.1
There is no known limit  to the force thus produced.  Its
expense alone limits its application.
  Conversely, magnetism may be converted into electri-
city.   Mr. Faraday observed that when a coil of wire,  the
ends of which  touched  each  other, was  placed on  the
armature  of a powerful  steel  magnet, and this armature
placed upon or taken from the poles, a  spark was visible
between  the ends of the coil.  And now the force thus
generated is being applied to the telegraph.  The alarms
of fire in Boston  are struck  by the force derived from
coils revolving between the poles of powerful magnets.
  But electricity can produce chemical action.  If a piece
of paper,  moistened with a solution of iodide  of potas-
sium, be placed between  the electrodes, the paper will be
stained brown from the iodine set  free.  And now  this
principle, expanded in the electrotype is used for a thou-
sand purposes.   Our books are printed  from electrotyped
1 Annual of Scientific Discovery, 1852, p. 99, 
33
plates.   Our table ware is silvered, and patent watches
are gilded, by this process.  If water be thus decomposed in
a close vessel the force generated is enormous.  Mr. Gassiot
has ruptured iron cylinders an inch thick in this manner.1
   That chemical action produces electricity I need hardly
stay to affirm, for it is the very means by which this pow-
erful agent is evolved.  Whenever chemical action of any
sort  takes place,  whenever  changes take place in the
composition  of matter, this subtle force is set free.   Says
Mr. Faraday, " The amount  of electricity set free by the
chemical action of a grain  of  water on four grains of zinc
is equal  to  that  evolved in a very heavy thunderstorm,"
and he is the world's best authority.2
   Nor need I stop to prove that chemical action produces
light.  We have such abundant evidence on  every  hand
that to make a  formal statement of the fact is to utter a
commonplace.   Every cottage has now the friction match
wherein mechanical force is converted into heat;  heat pro-
duces chemical action, which in its  turn produces the
heat  and light  of combustion.  The poorest peasant has
at hand the means of producing  light, which but a few
years since the richest noble could not obtain.   The old
tinder box is laughed at in this nineteenth century, yet it
contained the same principle, though in the germ.
  Light  produces chemical action in a thousand  ways.
Every amateur in chemistry has exposed mixed hydrogen
and chlorine  gases to the sunlight to witness their explo-
sive  union.   And every one of us has had an "impalpa-
ble scale," in the language of Dr. Holmes, taken from his
face  in the shape of  a photograph.   Every carte-de-visite
given or  received by the  hand  of  friendship is a silent
witness to the chemical action produced  by light.   The
sun is now our greatest artist.
  1 Tyndall on Heat, p. 94, note.
  2 Faraday, Experimental Researches, Vol. i, p. 257.
                 5 
34
  We have thus taken somewhat in detail the facts which
establish the  mutual convertibility or "correlation"  of
forces. And to my own mind they satisfactorily prove the
proposition made at the outset, that force is never lost; but
though it  may disappear in one form it reappears in ano-
ther,  and in exactly equivalent amount.
  We might  go a step farther and show that frequently
more than  one form of force is  developed at  the  same
time, and that it is owing to this  fact that it is so difficult
to estimate the value of any one force in terms of another.
One experiment of Mr. Grove is so striking and so con-
clusive that I must beg leave to describe it.  " A prepared
daguerreotype plate is inclosed in a box filled with water,
having a glass front with a shutter over it.  Between this
glass and the plate is a gridiron of silver wire;  the  plate
is connected with one extremity of a galvanometer  coil,
and the  gridiron of wire with one extremity  of a Bre-
guet's helix — an elegant instrument formed  by a coil of
two metals, the unequal expansion of which  indicates
slight changes in temperature — the other extremities of
the galvanometer and helix are connected by a  wire, and
the needles brought to zero.  As soon as a beam of  day-
light  or  of the electric light is, by raising the shutters,
permitted to impinge upon the plate the  needles are de-
flected.   Thus light being the initiating force, we get che-
mical action on the plate, electricity circulating through the
wires, magnetism in the coil, heat in the helix, and motion
in the needles." ]
  It was stated a few minutes since that the store of force
in the universe has not  diminished since the creation.
But it must be apparent to all  that the earth, in common
with the other planets, is continually losing heat by' radiat-
ing it into  space: and that unless this loss is made up, our
globe will soon be barren of life.   That  this loss is  com-
l Correlation of Physical Forces, London, 1855, p. 120. 
35
pensated, appears from the following facts.  We  have
seen  that  when bodies  cool, they  contract.  Rotating
bodies which contract, revolve more rapidly.   It has been
proved by M. Laplace that the time of rotation  of our
earth has not diminished 1-300 of a second for the 2,000
years since the time of Ilipparchus.  Hence we conclude
that it has not lost heat.   If I ask whence the  supply, I
am  instantly referred  to  the sun.   According  to the
estimates of M. Pouillet, the earth receives annually from
the  sun, sufficient heat to melt 5,400 pounds of ice  upon
every  square  foot of its surface;  if, therefore, the globe
were entirely covered with a shell  of ice 100 feet thick, it
would be melted by the sun in a  single year.1  Thus so
far as the heat of the  earth in concerned, we see  that its
source is the sun.  But perhaps we can prove that this is
true for all force upon the  earth.
   Go to any  one of those thriving manufacturing villages,
scattered all over our land.  There your eye rests on mas-
sive  six story  buildings,  from  whence  emanates  the
whirring of machinery.  You  enter,  and from  garret to
cellar, all is one incessant rattle.   Passing in at that door
are immense  bales of cotton, to be seized, picked to pieces,
and carded; the fibres being laid parallel, they are  divided
and  by a million of steel  fingers, twisted into threads, to
be then  spun into  different fabrics.  And  as  you pass
from floor to floor and wonder at the skill displayed in
this  mechanism, you ask the   source of the power which
renders it all available.  You are pointed to an open door,
within which you perceive an immense wheel, into whose
buckets water is constantly  pouring, causing  them to
descend and bring others to the task.   The power  you see
comes from falling water.   But how was it raised ?  Pass-
ing out of the cotton-mill you are shown the  canal, by
means of which,  the water from an adjacent stream is led
 1 Pouillet, Physique Experimental, Paris 1856, Tome 2, p. 714. 
36
to the water wheel.  You walk up along the banks of this
stream.   Here and there it receives tributary rills, grows
smaller as you ascend, till a clear bubbling spring reveals
its source.  Is not this water a gift to the spring from the
clouds ?  And was it not from the ocean and the lake that
the beams of the sun lifted it invisibly to the clouds ?   Is
it not a part of the sun's force then, which gives life to the
machinery of the mill ?
  But again.  Go down upon one of the wharves of our
metropolis and behold  that huge ocean  steamer.   The
hour for her departure has come.  The last bell has rung,
and as you look she moves slowly from her moorings and
without a  sail, passes majestically the  forts, through the
Narrows and  out upon  the  broad Atlantic.  Boldly she
buffets the waves, and though the  tempests  may wreak
their vengeance upon her, steadily she  moves on her way,
carrying safely to the goal her cargo of life.   If you ask
the means by which this is accomplished you  are pointed
to the enormous paddle wheels; but in,them  alone there
is no power.   You see  on board of her a huge mass of
machinery, complicated, but motionless.  Not far from it
are iron tanks full  of  water;  but they are equally im-
potent.  What shall give energy to all these appliances ?
That black  and  dirty coal, which just now  you shrank
from being defiled by, contains a power in its embrace
which is competent to the task.  Placed in the furnace
and ignited,  and water, machinery, and paddle wheels  are
 its servants, while it bows  its head to the will of man alone.
 Do you ask whence the coal obtained  its power ?  I refer
 you  to those past ages, when our  earth was in its ado-
 lescence.  The atmosphere was filled with carbonic acid,
 out of which all this coal was made.  The bright light of
 the sun, falling upon the green leaves which had absorbed
 this  gas, gave them power to store up the carbon in their
 tissues.   That carbon is  this coal.   And the sun-power 
37
which formed it is still stored up in it, as heat.  Is not the
sun's force the  agent which moves the steamship ?
  One step farther.  Out upon the broad ocean floats the
wealth  and pride of many nations.  The swift  winged
clipper  and the cumbrous frigate ;  the New York yacht
and the Dutch galliot alike spread their sails to  the
breezes of Heaven and are propelled  over  the waves.
These birds of the sea, fostered by the science of naviga-
tion, have  equalled the steamer in the  accuracy  of their
flight.  As the noble ship spreads  sail after sail  to the
breeze, which  wafts her away  until she appears like  a
white cloud upon the sea, you involuntarily pause to con-
sider whence the force which urges her  on.   Do you say
it is the action of the wind  upon her  sails ? But what
causes the wind ?  Is it not the  sun heating unequally the
earth's surface causing the air to rise, and cooler currents,
as wind, to rush in to  fill the space ?
  But neither the independent  steamship  nor the  wind-
urged clipper have, in themselves, any means of certainty
in their course. Formerly navigators were obliged  to sail
along the shore.  If  they missed sight of it they were
lost.   The narrow,  contracted Mediterranean  was  too
large for them.   Now the mariner pushes fearlessly out
into the boundless ocean, and crosses it as  accurately as if
he  were following a beaten  path.  Stand  by the side of
him who guides  that  ship.  By what rule does  he turn
her helm this  way or that ?   In the little  box you  see in
front of him is delicately balanced  a bar  of  steel, which
points out the  North with undeviating accuracy.  Guided
by this he need never go astray.  But what is the force
which keeps this tiny thing true to the pole ?  The earth's
magnetism.  How is  this produced ?  According to  pre-
sent science,  by electric  currents which circulate  round
the earth  parallel to the magnetic equator.  And the
cause of these  currents ?  The heat of the sun ! 
38
   Do you say, This is very well, so far.  But there is one
force which is  independent of the sun.  My own right
arm owes none of its might to the orb of day.  But let us
see. How is your body maintained in its integrity ? From
what source comes the muscular fibre which contracts to
produce the force ?   Is it not from your food ?  But this
fibre wastes in doing work.  An ordinary day's labor, con-
tinued for  eighty days without  supply, would destroy all
the muscles by oxidation.  But it is in this oxidation that
force is  produced.   And the food which  supplies  this
waste, this force, was, if vegetable, formed from the air by
the action of sunlight.  If your food was animal, the cause
is only a step farther back.  For the animal  derived his
flesh from the vegetable on which  he  fed.  " Not, there-
fore, in a poetical, but in a strictly mechanical sense, are
we the children of the sun."
   The greatest of England's engineers, George Stephenson,
once  asked Dr. Buckland,  then  Dean  of  Westminster,
" Can you tell me what  is the power that is driving that
train ?" alluding to a railway train passing at the moment.
The learned Dean answered, " I suppose it is one of your
big engines."  " But what drives the engine ?"   " Oh,
very likely a canny Newcastle driver."  "What  do you
say to the light of the sun ?"  " How can that be ?" asked
Buckland.   "It is nothing else," said Stephenson.  " It
is light bottled up in the earth for tens of thousands of
years ; light, absorbed  by plants  and vegetables, being
necessary for the condensation of carbon during the pro-
cess of their growth, if it be not carbon in another form;
and now after being buried in the earth for long  ages in
fields of coal, that latent light is again brought forth and
liberated, made to work,— as in that locomotive,—for great
human purposes."
   How vastly important then is our sun, as a reservoir of
force to our system.  Though emanating from  it only as 
39
light, we have, by the curious correlation now indicated,
all the forces produced which are in action upon our earth.
We are thus brought to consider our sun as a magazine of
force.   The amount of heat he radiates to the earth has
been already stated.  It would melt a crust of ice on the
earth's surface 100  feet thick,  annually.  As the  earth
receives only 1-2,300,000,000 of the heat sent forth, it fol-
lows that a layer of ice surrounding the sun at the distance
of our earth, and one hundred feet thick, would be  annu-
ally melted.  Transferring this  heat to the sun's surface,
we find that there it would melt a layer of ice forty feet thick
every minute, and one ten and a half miles thick annually}  It
would' boil  per hour seven hundred thousand millions  of cubic
miles of ice cold water.  It is equal per hour to that which would .
be generated by  the combustion of  a layer of coal ten feet thick,
entirely surrounding the sun; and per year, to such a layer of
coal, seventeen miles in thickness I
   If such  is the enormous loss of the sun, the question
must arise, how does the sun get its force ?  By what sort
of action is this enormous temperature maintained ?  Shall
we say by combustion ?   " Were the sun a solid block of
coal, and were it allowed a sufficient supply of oxygen to
enable it  to burn  at the  rate necessary to produce the
observed emission, it would be utterly consumed in  five
thousand  years."
   Shall we say that the sun is a cooling globe ?  " Assum-
ing the specific  heat of the sun to be the same as that of
water,—the terrestrial  substance  which  possesses  the
highest specific heat,— in  five thousand years, the entire
mass of the sun would cool down 15,000°.
   The sun  turns  on his axis once  in twenty-five days.
Can  it be friction of his periphery against anything in
surrounding space which produces this high temperature ?
Though we can not conceive of any such " brake,"  yet as
» Pouillet, Op. Cit., p. 716. 
40
we have the data,  " we can calculate the total amount of
heat which the sun could generate by such friction.  We
know  his mass, and his time of rotation ; we know also
the mechanical equivalent of heat.  From these data we
deduce that the entire  force of rotation, if converted into
heat, would cover more than one, but less than two centuries
of emission."   This theory is therefore untenable.
  Another proposition is  based  on the nebular theory of
M. Laplace.  This theory supposes the entire solar system
to have once been a nebulous mass, extending far beyond
the orbit of Neptune, the outermost planet.   The tenuity
of this mass must have been extreme.   Several cubic miles
of it would weigh  but a single grain.  Molecular attrac-
tion produced condensation, accompanied by a loss of heat.
The contraction toward the centre not  being uniform, a
rotary  motion was assumed by the mass, which  increased
in velocity with the diminution  in bulk.  Finally as the
condensation went  on  and the centrifugal exceeded the
central force, an exterior equatorial ring was thrown off,
which  soon ruptured into a planet.  Other planets were
thus formed, and in their turn produced satellites, until at
length the principal mass was condensed into the sun.
Now Prof. Helmholtz has  shown that the mechanical force
equivalent  to  the  mutual gravitation of the particles of
such a nebulous mass, would be 454 times the mechanical
force now in our system ; 453-454 of this force have been
already wasted as heat.  The 1-454 which remains, how-
ever, would raise a mass of water equal to the  sun  and
planets in weight, 28 millions of degrees Centigrade. The
heat of the oxyhydrogen blowpipe, sufficient to fuse  and
vaporize  even  platinum, is  but 2,000° C.  If the mass of
our entire system were pure coal, by the combustion of
the whole  of  it, only the  3,500th  part of the  above
enormous quantity would be generated.  If this conden-
sation is still going on, it  may be calculated that if  the 
41
 diameter of the sun were diminished only the ten-thou-
 sandth part of its present length, by this act a sufficient
 quantity  of heat would be generated to cover the total
 emissions for 2,100 years.  Such a small change it would
 be difficult to detect even by the finest astronomical obser-
 vations.1
   There is one other theory which, however bold it may
 at first sight appear, deserves our earnest attention.  This
 is  "the meteoric theory of  the sun's heat."   We know
 that  the  interplanetary space is far from empty.  That
 besides planets,  satellites and comets, there are innumer-
 able smaller yet ponderable bodies, all circulating in orbits
 about the central sun.  These bodies sometimes cross the
 outer limits of our  atmosphere, and being ignited appear
 as meteors.  Those  who have watched the heavens on a
 clear night know how frequent are these " shooting stars."
 At certain times they appear in vast numbers.  In Boston
 240,000 were observed in nine hours.  The whole annual
 number would be estimated by hundreds or thousands of
 millions,  and yet how infinitesimally small a portion of
 those falling to the sun pass  near the earth.   Moreover,
 from observations made upon  Encke's  comet, and from
 other data, we know that space  is filled  with a resisting
 medium,  though excessively  tenuous.  The effect of this
 upon the  larger planets in lessening their distance  from
 the sun,  and consequently quickening their revolutions
 about it, though not appreciable, may yet be considerable
 in the  case  of the  smaller bodies, which may be  rapidly-
 approaching the sun.  We have already noticed the heat
 occasioned by the fall of bodies to the earth.  In the place
 of the planet let us set the sun, with 300,000 times the
 earth's mass, and instead of a fall of a few feet let us take
the cosmical elevations, and we then obtain a means of gene-

  lProf. Helmholtz, Interaction of Natural Forces, Phil. Mag., IV Series,
Vol. xi, pp. 506, 514.
                 6 
42
rating heat which transcends all terrestrial power.  If an
asteroid falls  directly to the sun we find that its  velocity
just before striking would be 390 miles per second; if it
revolve around the sun close to his surface, 276 miles  per
second.  In the former case the heat developed simply by
the  mechanical collision would be  9,000 times that pro-
duced by the combustion of an  equal asteroid  of solid
coal.  In the latter it would be equal to that produced by
the combustion of 4,000 such asteroids.  If all the planets
were to fall into the sun, the heat thus produced would
cover the total emission for 45,589 years.   Here then we
have an agency competent to restore his  lost agency to
the  sun.   Though the very quality of the solar rays ena-
bles us to infer that the temperature  of their origin must
be enormous, yet in the fall of asteroids we find the means
of producing  such a temperature.   Of course this  shower-
ing  down of matter upon the sun must produce  an aug-
mentation of its size.  " But the amount of this increase,
which would  be  sufficient to cover the calorific emission
for 4,000 years, could not be detected by our most  delicate
instruments.   If the earth struck the sun it would utterly
vanish from  perception, but the heat developed by  its
shock would cover the expenditure of the  sun for a  cen-
tury."
  Such is the beautiful theory of Mayer, published  in 1848,
in his  "Dynamik des Himmels."   Says Prof. Thompson,
following out the same idea:  " The  source then from
which solar heat is derived is undoubtedly meteoric.  The
principal source, perhaps the  sole  appreciable  efficient
source, is in bodies circulating around the sun,  at present
inside the earth's orbit, and  probably seen by  us in  the
sunlight, called the zodiacal light.  The store of energy
for future  sunlight is  at present  partly dynamical, that
of the motions of these bodies round the  sun, and partly
potential, that of their  gravitation toward the sun.  The
latter  is  gradually  being spent, half against the resisting 
43
medium, and half in causing a continuous increase of the
former.  Each meteor thus goes on moving  faster  and
faster, and getting  nearer  and nearer the centre, until
some time very suddenly it gets so much entangled in the
solar atmosphere as to begin to lose velocity.  In a  few
seconds more  it is  at rest on  the sun's surface, and the
energy given up  is vibrated across the district where it
was gathered  during  so many ages, ultimately to pene-
trate, as light,  the remotest regions of space." 1
   Thus starting from some of those simple facts of nature
which seem hardly to merit attention, and following them
back to their  origin,  we find them linked together in a
chain reaching throughout the solar system.  One end is
in  the sun; the  other binds together planet and satellite
in a common brotherhood.  From  that  sun  all get life.
It is the universal parent.  In the eloquent words  of Mr.
Tyndall:  " As surely  as the force which moves a clock's
hands is derived from  the arm which winds up the clock,
so  surely  is all  terrestrial  power drawn  from the sun.
Leaving out of account the eruptions  of  volcanoes and
the ebb and flow of the tides, every mechanical action on
the earth's surface, every manifestation  of  power, organic
and inorganic,  vital  and physical, is produced'by the sun.
His warmth keeps the sea liquid and the atmosphere a
gas, and all the storms which  agitate both  are blown by
the mechanical force of the sun.  He lifts the rivers and
the glaciers up to the  mountains, and  thus  the cataract
and the  avalanche shoot with an energy  derived imme-
diately from him.  Thunder and lightning  are also  his
transmuted strength.  Every fire that  burns  and  every
flame that glows dispenses light and heat which originally
belonged to the sun.   In these days, unhappily, the news
of battle is familiar to  us, but every  shock  and  every
charge is an application or misapplication of the mechan-
  1 Prof. Wm. Thompson, Trans. Royal Soc, Edinburgh, 1854. 
44
ical force of the sun.   He blows the trumpet, he urges
the projectile, he bursts the bomb ; and remember this is
not poetry,  but  rigid  mechanical truth.  He rears  the
whole vegetable world, and through  it  the  animal;  the
lilies of the field are  his workmanship, the verdure  of the
meadows, and the cattle upon  a thousand hills.  He  forms
the muscle, he urges  the blood, he builds the brain.  His
fleetness is in the lion's foot, he springs in the panther, he
soars in the eagle, he slides in the snake.  He builds  the
forest and hews it down ; the power which raised the tree
and which wields the axe  being one and the same.   The
clover sprouts and blossoms, and  the scythe of the mower
swings  by the operations of  the same force.   The sun
digs the ore from our mines, he rolls the iron, he  rivets
the plates, he boils the  water, he draws the train.  He
not only grows  the  cotton, but  he spins the fibre and
weaves the web.   There is not a  hammer raised, a wheel
turned,  or a shuttle thrown, that is not raised, and turned
and thrown by the sun.  His  energy is poured freely into
space, but  our world is a halting place where this energy
is conditioned.   Here the  Proteus works his  spells;  the
self same essence  takes a million shapes and hues, and
finally dissolves into its primitive and  almost formless
form.  The  sun comes to us as heat; he quits us as heat;
and  between his entrance and departure the  multiform
powers  of our globe appear.   They are all special forms
of solar power — the  moulds  into which his  strength is
temporarily  poured  in  passing from  its  source through
infinitude.  To nature nothing can be added; from nature
nothing can be taken away: the  sum of her energies is
constant, and the  utmost man can do in the pursuit of
physical knowledge  is  to shift  the  constituents of the
never varying'total, and out of one of  them to form ano-
ther.    The  law of conservation rigidly excludes both
creation and annihilation.  Waves may change to ripples 
45
and ripples to waves — magnitude may be substituted  for
number and number for magnitude — asteroids may aggre-
gate to suns,  suns may resolve themselves into florae and
faunae, and florae and faunae melt into air—the  flux of
power is eternally the same.  It rolls in  music through
the ages, and all terrestrial energy — the manifestations of
life as well as the display of phenomena — are but the mo-
dulations of its rhythm."