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variations, to the proofs of the value of the principle laid down,
the consistency of the known phenomena with it, and the sug-



1857.] The Heat Force. 453

gestions of research and discovery which arise from it*. Heat,
for instance, is a mighty form of power, and its effects have
been greatly developed ; therefore, assumptions regarding its
nature become useful and necessary, and philosophers try to
define it. The most probable assumption is, that it is a mo-
tion of the particles of matter ; but a view, at one time very
popular, is, that it consists of a particular fluid of heat.
Whether it be viewed in one way or the other, the principle of
conservation is admitted, I believe, with all its force. When
transferred from one portion to another portion of like matter,
the full amount of heat appears. When transferred to matter
of another kind, an apparent excess or deficiency often results';
the word " capacity " is then introduced, which, whilst it ac-
knowledges the principle of conservation, leaves space for re-
search. When employed in changing the state of bodies, the
appearance and disappearance of the heat is provided for con-
sistently by the assumption of enlarged or diminished motion,
or else space is left by the term " capacity" for the partial views
which remain to be developed. When converted into me-
chanical force, in the steam- or air-engine, and so brought into
direct contact with gravity, being then easily placed in rela-
tion to it, still the conservation of force is fully respected and
wonderfully sustained. The constant amount of heat developed
in the whole of a voltaic current described by M. P. A. Favref ,
and the present state of the knowledge of thermo-electricity,
are again fine partial or subordinate illustrations of the prin-
ciple of conservation. Even when rendered radiant, and for the
time giving no trace or signs of ordinary heat action, the as-
sumptions regarding its nature have provided for the belief in
the conservation of force, by admitting, either that it throws
the ether into an equivalent state, in sustaining which for the
time the power is engaged ; or else, that the motion of the
particles of heat is employed altogether in their own transit
from place to place.

It is true that heat often becomes evident or insensible in a
manner unknown to us ; and we have a right to ask what is
happening when the heat disappears in one part, as of the

* Helmholtz, " On the Conservation of Force." Taylor's ' Scientific Me-
moirs/ 2nd series, 1853, p. 114.
t Comptes Rendus, 1854, vol. xxxix. p. 1212.



454 On the Conservation of Force. [1857.

thermo-voltaic current, and appears in another ; or when it
enlarges or changes the state of bodies ; or what would happen,
if the heat being presented, such changes were purposely op-
posed. We have a right to ask these questions, but not to
ignore or deny the conservation of force ; and one of the high-
est uses of the principle is to suggest such inquiries. Expli-
cations of similar points are continually produced, and will be
most abundant from the hands of those who, not desiring to
ease their labour by forgetting the principle, are ready to admit
it either tacitly, or better still, effectively, being then continu-
ally guided by it. Such philosophers believe that heat must do
its equivalent of work ; that if in doing work it seem to disap-
pear, it is still producing its equivalent effect, though often in
a manner partially or totally unknown ; and that if it give rise
to another form of force (as we imperfectly express it), that force
is equivalent in power to the heat which has disappeared.

What is called chemical attraction^ affords equally instruct-
ive and suggestive considerations in relation to the principle
of the conservation offeree. The indestructibility of individual
matter is one case, and a most important one, of the conserva-
tion of chemical force. A molecule has been endowed with
powers which give rise in it to various qualities, and these never
change, either in their nature or amount. A particle of oxygen
is ever a particle of oxygen nothing can in the least wear it.
If it enters into combination and disappears as oxygen, if it
pass through a thousand combinations, animal, vegetable, mi-
neral, if it lie hid for a thousand years and then be evolved,
it is oxygen with its first qualities, neither more nor less. It
has all its original force, and only that ; the amount of force
which it disengaged when hiding itself, has again to be em-
ployed in a reverse direction when it is set at liberty ; and if,
hereafter, we should decompose oxygen, and find it com-
pounded of other particles, we should only increase the strength
of the proof of the conservation of force, for we should have a
right to say of these particles, long as they have been hidden,
all that we could say of the oxygen itself.

Again, the body of facts included in the theory of definite
proportions, witnesses to the truth of the conservation of force ;
and though we know little of the cause of the change of pro-
perties of the acting and produced bodies, or how the forces of



1 857.] The Chemical Force The Dual Forces. 455

the former are hid amongst those of the latter, we do not for
an instant doubt the conservation, but are moved to look for
the manner in which the forces are, for the time, disposed, or if
they have taken up another form of force, to search what that
form may be.

Even chemical action at a distance, which is in such antithe-
tical contrast with the ordinary exertion of chemical affinity,
since it can produce effects miles away from the particles on
which they depend, and which are effectual only by forces
acting at insensible distances, still proves the same thing, the
conservation of force. Preparations can be made for a che-
mical action in the simple voltaic circuit, but until the circuit
be complete that action does not occur ; yet in completing we
can so arrange the circuit, that a distant chemical action, the
perfect equivalent of the dominant chemical action, shall be
produced ; and this result, whilst it establishes the electro-
chemical equivalent of power, establishes the principle of the
conservation of force also, and at the same time suggests many
collateral inquiries which have yet to be made and answered,
before all that concerns the conservation in this case can be
understood.

This and other instances of chemical action at a distance,
carry our inquiring thoughts on from the facts to the physical
mode of the exertion of force'; for the qualities which seem
located and fixed to certain particles of matter appear at a di-
stance in connexion with particles altogether different. They
also lead our thoughts to the conversion of one form of power
into another : as for instance, in the heat which the elements of
a voltaic pile may either show at the place where they act by
their combustion or combination together ; or in the distance,
where the electric spark may be rendered manifest ; or in the
wire or fluids of the different parts of the circuit.

When we occupy ourselves with the dual forms of power,
electricity and magnetism, we find great latitude of assumption ;
and necessarily so, for the powers become more and more
complicated in their conditions. But still there is no apparent
desire to loosen the force of the principle of conservation,
even in those cases where the appearance and disappearance
of force may seem most evident and striking. Electricity ap-
pears when there is consumption of no other force than that



456 On the Conservation of Force. [1857.

required for friction ; we do not know how, but we search to
know, not being willing to admit that the electric force can
arise out of nothing. The two electricities are developed in
equal proportions ; and having appeared, we may dispose
variously of the influence of one upon successive portions of
the other, causing many changes in relation, yet never able to
make the sum of the force of one kind in the least degree ex-
ceed or come short of the sum of the other. In that necessity
of equality, we see another direct proof of the conservation of
force, in the midst of a thousand changes that require to be
developed in their principles before we can consider this part
of science as even moderately known to us.

One assumption with regard to electricity is, that there is
an electric fluid rendered evident by excitement in plus and
minus proportions. Another assumption is, that there are two
fluids of electricity, each particle of each repelling all particles
like itself, and attracting all particles of the other kind always,
and with a force proportionate to the inverse square of the di-
stance, being so far analogous to the definition of gravity.
This hypothesis is antagonistic to the law of the conservation of
force, and open to all the objections that have been, or may
be, made against the ordinary definition of gravity. Another
assumption is, that each particle of the two electricities has a
given amount of power, and can only attract contrary particles
with the sum of that amount, acting upon each of two with
only half the power it could in like circumstances exert upon
one. But various as are the assumptions, the conservation of
force (though wanting in the second) is, I think, intended to
be included in all. I might repeat the same observations
nearly in regard to magnetism, whether it be assumed as a
fluid, or two fluids or electric currents, whether the external
action be supposed to be action at a distance, or dependent on
an external condition and lines of force still all are intended
to admit the conservation of power as a principle to which the
phenomena are subject.

The principles of physical knowledge are now so far de-
veloped as to enable us not merely to define or describe the
known t but to state reasonable expectations regarding the
unknown ; and I think the principle of conservation of force
may greatly aid experimental philosophers in that duty to



1857.] On the Conservation of Force. 457

science, which consists in the enunciation of problems to be
solved. It will lead us, in any case where the force remaining
unchanged in form is altered in direction only, to look for the
new disposition of the force ; as in the cases of magnetism,
static electricity, and perhaps gravity, and to ascertain that, as
a whole, it remains unchanged in amount : or, if the original
force disappear, either altogether or in part, it will lead us to
look for the new condition or form of force which should result,
and to develope its equivalency to the force that has disappeared.
Likewise, when force is developed, it will cause us to consider
the previously existing equivalent to the force so appearing ;
and many such cases there are in chemical action. When
force disappears, as in the electric or magnetic induction after
more or less discharge, or that of gravity with an increasing
distance, it will suggest a research as to whether the equivalent
change is one within the apparently acting bodies, or one ex-
ternal (in part) to them. It will also raise up inquiry as to the
nature of the internal or external state, both before the change
and after. If supposed to be external, it will suggest the
necessity of a physical process, by which the power is com-
municated from body to body ; and in the case of external
action, will lead to the inquiry, whether, in any case, there can
be truly action at a distance, or whether the ether, or some
other medium, is not necessarily present.

We are not permitted as yet to see the nature of the source
of physical power, but we are allowed to see much of the con-
sistency existing amongst the various forms in which it is pre-
sented to us. Thus if, in static electricity, we consider an act
of induction, we can perceive the consistency of all other like
acts of induction with it. If we then take an electric current,
and compare it with this inductive effect, we see their relation
and consistency. In the same manner we have arrived at a
knowledge of the consistency of magnetism with electricity ;
and also of chemical action and of heat with all the former ;
and if we see not the consistency between gravitation with any
of these forms of force, I am strongly of the mind that it is
because of our ignorance only. How imperfect would our idea
of an electric current now be, if we were to leave out of sight
its origin, its state and dynamic induction, its magnetic influ-
ence, its chemical and heating effects ! or our idea of any one



458 On the Conservation of Force. [1857.

of these results, if we left any of the others unregarded! That
there should be a power of gravitation existing by itself, having
no relation to the other natural powers, and no respect to the
law of the conservation of force, is as little likely as that there
should be a principle of levity as well as of gravity. Gravity
may be only the residual part of the other forces of nature, as
Mossotti has tried to show ; but that it should fall out from
the law of all other force, and should be outside the reach
either of further'experiment or philosophical conclusions, is not
probable. So we must strive to learn more of this outstanding
power, and endeavour to avoid any definition of it which is in-
compatible with the principles of force generally, for all the
phenomena of nature lead us to believe that the great and
governing law is one. I would much rather incline to believe
that bodies affecting each other by gravitation act by lines of
force of definite amount (somewhat in the manner of magnetic
or electric induction, though without polarity), or by an ether
pervading all parts of space, than admit that the conservation
of force could be dispensed with.

It may be supposed, that one who has little or no mathe-
matical knowledge should hardly assume a right to judge of
the generality and force of a principle such as that which forms
the subject of these remarks. My apology is this : I do not
perceive that a mathematical mind, simply as such, has any
advantage over an equally acute mind not mathematical, in
perceiving the nature and power of a natural principle of action.
It cannot of itself introduce the knowledge of any new principle.
Dealing with any and every amount of static electricity, the
mathematical mind can, and has balanced and adjusted them
with wonderful advantage, and has foretold results which the
experimentalist can do no more than verify. But it could not
discover dynamic electricity, nor electro-magnetism, nor mag-
neto-electricity, or even suggest them ; though when once dis-
covered by the experimentalist, it can take them up with ex-
treme facility. So in respect of the force of gravitation, it has
calculated the results of the power in such a wonderful manner
as to trace the known planets through their courses and per-
turbations, and in so doing has discovered a planet before un-
known; but there may be results of the gravitating force of
other kinds than attraction inversely as the square of the di*-



1857.] The gravitating Force. 459

stance, of which it knows nothing, can discover nothing, and can
neither assert nor deny their possibility or occurrence. Under
these circumstances, a principle, which may be accepted as
equally strict with mathematical knowledge, comprehensible
without it, applicable by all in their philosophical logic whatever
form that may take, and above all, suggestive, encouraging, and
instructive to the mind of the experimentalist, should be the
more earnestly employed and the more frequently resorted to
when we are labouring either to discover new regions of science,
or to map out and develope those which are known into one
harmonious whole ; and if in such strivings, we, whilst applying
the principle of conservation, see but imperfectly, still we should
endeavour to see, for even an obscure and distorted vision is
better than none. Let us, if we can, discover a new thing in
any shape ; the true appearance and character will be easily
developed afterwards.

Some are much surprised that I should, as they think, venture
to oppose the conclusions of Newton: but here there is a
mistake. I do not oppose Newton on any point ; it is rather
those who sustain the idea of action at a distance that contradict
him. Doubtful as I ought to be of myself, I am certainly very
glad to feel that my convictions are in accordance with his
conclusions. At the same time, those who occupy themselves
with such matters ought not to depend altogether upon au-
thority, but should find reason within themselves, after careful
thought and consideration, to use and abide by their own
judgment. Newton himself, whilst referring to those who
were judging his views, speaks of such as are competent to form
an opinion in such matters, and makes a strong distinction
between them and those who were incompetent for the case.

But, after all, the principle of the conservation of force may
by some be denied. Well, then, if it be unfounded even in its
application to the smallest part of the science of force, the
proof must be within our reach, for all physical science is so.
In that case, discoveries as large or larger than any yet made
may be anticipated. I do not resist the search for them, for
no one can do harm, but only good, who works with an earnest
and truthful spirit in such a direction. But let us not admit
the destruction or creation of force without clear and constant
proof. Just as the chemist owes all the perfection of his science



460 On the Conservation of Force. [1858.

to his dependence on the certainty of gravitation applied by the
balance, so may the physical philosopher expect to find the
greatest security and the utmost aid in the principle of the
conservation of force. All that we have that is good and safe,
as the steam-engine, the electric telegraph, &c., witness to that
principle, it would require a perpetual motion, a fire without
heat, heat without a source, action without reaction, cause
without effect, or effect without a cause, to displace it from its
rank as a law of nature.



During the year that has passed since the publication of the
preceding views regarding gravitation, &c., I have come to the
knowledge of various observations upon them, some adverse,
others favourable ; these have given me no reason to change my
own mode of viewing the subject, but some of them make me
think that I have not stated the matter with sufficient precision.
The word " force " is understood by many to mean simply "the
tendency of a body to pass from one place to another," which
is equivalent, I suppose, to the phrase " mechanical force ; "
those who so restrain its meaning must have found my argument
very obscure. What I mean by the word " force," is the cause
of a physical action ; the source or sources of all possible
changes amongst the particles or materials of the universe.

It seems to me that the idea of the conservation of force is
absolutely independent of any notion we may form of the nature
of force or its varieties, and is as sure and may be as firmly
held in the mind, as if we, instead of being very ignorant,
understood perfectly every point about the cause of force and
the varied effects it can produce. There may be perfectly
distinct and separate causes of what are called chemical actions,
or electrical actions, or gravitating actions, constituting so many
forces; but if the "conservation of force" is a good and true
principle, each of these forces must be subject to it : none can
vary in its absolute amount ; each must be definite at all times,
whether for a particle, or for all the particles in the universe ;
and the sum also of the three forces must be equally unchange-
able. Or, there may be but one cause for these three sets of
actions, and in place of three forces we may really have but one,
convertible in its manifestations ; then the proportions between
one set of actions and another, as the chemical and the electrical,



1858.] On the Conservation of Force. 461

may become very variable, so as to be utterly inconsistent with
the idea of the conservation of two separate forces (the elec-
trical and the chemical), but perfectly consistent with the con-
servation of a force being the common cause of the two or
more sets of action.

It is perfectly true that we cannot always trace a force by its
actions, though we admit its conservation. Oxygen and hy-
drogen may remain mixed for years without showing any signs
of chemical activity ; they may be made at any given instant to
exhibit active results, and then assume a new state, in which again
they appear as passive bodies. Now, though we cannot clearly
explain what the chemical force is doing, that is to say, what
are its effects during the three periods before, at, and after
the active combination, and only by very vague assumption can
approach to a feeble conception of its respective states, yet we
do not suppose the creation of a new portion of force for the
active moment of time, or the less believe that the forces
belonging to the oxygen and hydrogen exist unchanged in
their amount at all these periods, though varying in their
results. A part may at the active moment be thrown off as
mechanical force, a part as radiant force, a part disposed of we
know not how ; but believing, by the principle of conservation,
that it is not increased or destroyed, our thoughts are directed
to search out what at all and every period it is doing, and how
it is to be recognized and measured. A problem, founded on
the physical truth of nature, is stated, and, being stated, is
on the way to its solution.

Those who admit the possibility of the common origin of all
physical force, and also acknowledge the principle of conserva-
tion, apply that principle to the sum total of the force. Though
the amount of mechanical force (using habitual language for
convenience sake) may remain unchanged and definite in its cha-
racter for a long time, yet when, as in the collision of two equal
inelastic bodies, it appears to be lost, they find it in the form
of heat and whether they admit that heat to be a continued
mechanical action (as is most probable), or assume some other
idea, as that of electricity, or action of a heat-fluid, still they
hold to the principle of conservation by admitting that the sum
of force, i. e. of the "cause of action," is the same, whatever
character the effects assume. With them the convertibility of



462 On the Conservation of Force. [1858.

heat, electricity, magnetism, chemical action and motion is a
familiar thought ; neither can I perceive any reason why they
should be led to exclude, a priori, the cause of gravitation
from association with the cause of these other phenomena re-
spectively. All that they are limited by in their various investiga-
tions, whatever directions they may take, is the necessity of
making no assumption directly contradictory of the conservation
of force applied to the sum of all the forces concerned, and to
endeavour to discover the different directions in which the
various parts of the total force have been exerted.

Those who admit separate forces inter-unchangeable, have
to show that each of these forces is separately subject to the
principle of conservation. If gravitation be such a separate
force, and yet its power in the action of two particles be sup-
posed to be diminished fourfold by doubling the distance, surely
some new action, having true gravitation character, and that
alone, ought to appear ; for how else can the totality of the force
remain unchanged? To define the force as " a simple attractive
force exerted between any two or all the particles of matter,
with a strength varying inversely as the square of the distance,"
is not to answer the question; nor does it indicate or even
assume what are the other complementary results which occur ;
or allow the supposition that such are necessary: it is simply,
as it appears to me, to deny the conservation of force.

As to the gravitating force, I do not presume to say that I
have the least idea of what occurs in two particles when their
power of mutually approaching each other is changed by
their being placed at different distances ; but I have a strong
conviction, through the influence on my mind of the doctrine
of conservation, that there is a change ; and that the phe-
nomena resulting from the change will probably appear some
day as the result of careful research. If it be said that
" 'twere to consider too curiously to consider so," then I must
dissent. To refrain to consider, would be to ignore the principle



Online LibraryMichael FaradayExperimental researches in chemistry and physics → online text (page 45 of 49)