THE CORRELATION AND EQUIVALENCE OF FORCES.
§ 77. When, to the unaided senses, Science began to add supplementary
senses in the shape of measuring instruments, men began to perceive
various phenomena which eyes and fingers could not distinguish. Of known
forms of force, minuter manifestations became appreciable; and forms of
force before unknown were rendered cognizable and measurable. Where
forces had apparently ended in nothing, and had been carelessly supposed
to have actually done so, instrumental observation proved that effects
had in every instance been produced: the forces reappearing in new
shapes. Hence there has at length arisen the inquiry whether the force
displayed in each surrounding change, does not in the act of expenditure
undergo metamorphosis into an equivalent amount of some other force or
forces. And to this inquiry experiment is giving an affirmative answer,
which becomes day by day more decisive. Grove, Helmholtz, and Meyer, are
more than any others to be credited with the clear enunciation of this
doctrine. Let us glance at the evidence on which it rests.
Motion, wherever we can directly trace its genesis, we find to pre-exist
as some other mode of force. Our own voluntary acts have always certain
sensations of muscular tension as their antecedents. When, as in letting
fall a relaxed limb, we are conscious of a bodily movement requiring no
effort, the explanation is that the effort was exerted in raising the
limb to the position whence it fell. In this case, as in the case of an
inanimate body descending to the Earth, the force accumulated by the
downward motion is just equal to the force previously expended in the
act of elevation. Conversely, Motion that is arrested produces,
under different circumstances, heat, electricity, magnetism, light. From
the warming of the hands by rubbing them together, up to the ignition of
a railway-brake by intense friction—from the lighting of detonating
powder by percussion, up to the setting on fire a block of wood by a few
blows from a steam-hammer; we have abundant instances in which heat
arises as Motion ceases. It is uniformly found, that the heat generated
is great in proportion as the Motion lost is great; and that to diminish
the arrest of motion, by diminishing the friction, is to diminish the
quantity of heat evolved. The production of electricity by Motion is
illustrated equally in the boy’s experiment with rubbed sealing-wax, in
the common electrical machine, and in the apparatus for exciting
electricity by the escape of steam. Wherever there is friction between
heterogeneous bodies, electrical disturbance is one of the consequences.
Magnetism may result from Motion either immediately, as through
percussion on iron, or mediately as through electric currents previously
generated by Motion. And similarly, Motion may create light; either
directly, as in the minute incandescent fragments struck off by violent
collisions, or indirectly, as through the electric spark. “Lastly,
Motion may be again reproduced by the forces which have emanated from
Motion; thus, the divergence of the electrometer, the revolution of the
electrical wheel, the deflection of the magnetic needle, are, when
resulting from frictional electricity, palpable movements reproduced by
the intermediate modes of force, which have themselves been originated
by motion.”
That mode of force which we distinguish as Heat, is now generally
regarded by physicists as molecular motion—not motion as displayed in
the changed relations of sensible masses to each other, but as occurring
among the units of which such sensible masses consist. If we cease to
think of Heat as that particular sensation given to us by bodies in
certain conditions, and consider the phenomena otherwise presented by
these bodies, we find that motion, either in them or in surrounding
bodies, or in both, is all that we have evidence of. With one or two
exceptions which are obstacles to every theory of Heat, heated bodies
expand; and expansion can be interpreted only as a movement of the units
of a mass in relation to each other. That so-called radiation through
which anything of higher temperature than things around it, communicates
Heat to them, is clearly a species of motion. Moreover, the evidence
afforded by the thermometer that Heat thus diffuses itself, is simply a
movement caused in the mercurial column. And that the molecular motion
which we call Heat, may be transformed into visible motion, familiar
proof is given by the steam-engine; in which “the piston and all its
concomitant masses of matter are moved by the molecular dilatation of
the vapour of water.” Where Heat is absorbed without apparent
result, modern inquiries show that decided though unobtrusive changes
are produced: as on glass, the molecular state of which is so far
changed by heat, that a polarized ray of light passing through it
becomes visible, which it does not do when the glass is cold; or as on
polished metallic surfaces, which are so far changed in structure by
thermal radiations from objects very close to them, as to retain
permanent impressions of such objects. The transformation of Heat into
electricity, occurs when dissimilar metals touching each other are
heated at the point of contact: electric currents being so induced.
Solid, incombustible matter introduced into heated gas, as lime into the
oxyhydrogen flame, becomes incandescent; and so exhibits the conversion
of Heat into light. The production of magnetism by Heat, if it cannot be
proved to take place directly, may be proved to take place indirectly
through the medium of electricity. And through the same medium may be
established the correlation of Heat and chemical affinity—a correlation
which is indeed implied by the marked influence that Heat exercises on
chemical composition and decomposition.
The transformations of Electricity into other modes of force, are still
more clearly demonstrable. Produced by the motion of heterogeneous
bodies in contact, Electricity, through attractions and repulsions, will
immediately reproduce motion in neighbouring bodies. Now a current of
Electricity generates magnetism in a bar of soft iron; and now the
rotation of a permanent magnet generates currents of Electricity. Here
we have a battery in which from the play of chemical affinities an
electric current results; and there, in the adjacent cell, we have an
electric current effecting chemical decomposition. In the conducting
wire we witness the transformation of Electricity into heat; while in
electric sparks and in the voltaic arc we see light produced. Atomic
arrangement, too, is changed by Electricity: as instance the transfer of
matter from pole to pole of a battery; the fractures caused by the
disruptive discharge; the formation of crystals under the influence of
electric currents. And whether, conversely, Electricity be or be not
directly generated by re-arrangement of the atoms of matter, it is at
any rate indirectly so generated through the intermediation of
magnetism.
How from Magnetism the other physical forces result, must be next
briefly noted—briefly, because in each successive case the illustrations
become in great part the obverse forms of those before given. That
Magnetism produces motion is the ordinary evidence we have of its
existence. In the magneto-electric machine we see a rotating magnet
evolving electricity. And the electricity so evolved may immediately
after exhibit itself as heat, light, or chemical affinity. Faraday’s
discovery of the effect of Magnetism on polarized light, as well as the
discovery that change of magnetic state is accompanied by heat, point to
further like connexions. Lastly, various experiments show that the
magnetization of a body alters its internal structure; and that
conversely, the alteration of its internal structure, as by mechanical
strain, alters its magnetic condition.
Improbable as it seemed, it is now proved that from Light also may
proceed the like variety of agencies. The solar rays change the atomic
arrangements of particular crystals. Certain mixed gases, which do not
otherwise combine, combine in the sunshine. In some compounds Light
produces decomposition. Since the inquiries of photographers have drawn
attention to the subject, it has been shown that “a vast number of
substances, both elementary and compound, are notably affected by this
agent, even those apparently the most unalterable in character, such as
metals.” And when a daguerreotype plate is connected with a proper
apparatus “we get chemical action on the plate, electricity circulating
through the wires, magnetism in the coil, heat in the helix, and motion
in the needles.”
The genesis of all other modes of force from Chemical Action, scarcely
needs pointing out. The ordinary accompaniment of chemical combination
is heat; and when the affinities are intense, light also is, under fit
conditions, produced. Chemical changes involving alteration of bulk,
cause motion, both in the combining elements and in adjacent masses of
matter: witness the propulsion of a bullet by the explosion of
gunpowder. In the galvanic battery we see electricity resulting from
chemical composition and decomposition. While through the medium of this
electricity, Chemical Action produces magnetism.
These facts, the larger part of which are culled from Mr. Grove’s work
on “The Correlation of Physical Forces,” show us that each force is
transformable, directly or indirectly, into the others. In every change
Force undergoes metamorphosis; and from the new form or forms it
assumes, may subsequently result either the previous one or any of the
rest, in endless variety of order and combination. It is further
becoming manifest that the physical forces stand not simply in
qualitative correlations with each other, but also in quantitative
correlations. Besides proving that one mode of force may be transformed
into another mode, experiments illustrate the truth that from a definite
amount of one, definite amounts of others always arise. Ordinarily it is
indeed difficult to show this; since it mostly happens that the
transformation of any force is not into some one of the rest but into
several of them: the proportions being determined by the ever-varying
conditions. But in certain cases, positive results have been reached.
Mr. Joule has ascertained that the fall of 772 lbs. through one foot,
will raise the temperature of a pound of water one degree of Fahrenheit.
The investigations of Dulong, Petit and Neumann, have proved a relation
in amount between the affinities of combining bodies and the heat
evolved during their combination. Between chemical action and voltaic
electricity, a quantitative connexion has also been established:
Faraday’s experiments implying that a specific measure of electricity is
disengaged by a given measure of chemical action. The well-determined
relations between the quantities of heat generated and water turned into
steam, or still better the known expansion produced in steam by each
additional degree of heat, may be cited in further evidence. Whence it
is no longer doubted that among the several forms which force assumes,
the quantitative relations are fixed. The conclusion tacitly agreed on
by physicists, is, not only that the physical forces undergo
metamorphoses, but that a certain amount of each is the constant
equivalent of certain amounts of the others.
* * * * *
§ 78. Throughout Evolution under all its phases, this truth of course
invariably holds. Every successive change or group of changes forming
part of it, is of necessity limited by the conditions thus implied. The
forces which any step in Evolution exhibits, must be affiliable on the
like or unlike forces previously existing; while from the forces so
generated must thereafter be derived others more or less transformed.
And besides recognizing the forces at any time existing, as necessarily
linked with those preceding and succeeding them, we must also recognize
the amounts of these forces successively manifested as determinate,—as
necessarily producing such and such quantities of results, and as
necessarily limited to those quantities.
Involved as are the phenomena of Evolution, it is not to be expected
that a _definite_ quantitative relation can in each case, or indeed in
any case, be shown between the forces expended in successive phases. We
have not adequate data for this; and probably shall never have them. The
antecedents of the simpler forms of Evolution, belong to a remote past
respecting which we can have nothing but inferential knowledge; while
the antecedents of the only kind of Evolution which is traceable from
beginning to end (namely, that of individual organisms) are too complex
to be dealt with by exact methods. Hence we cannot hope to establish
_equivalence_ among the successive manifestations of force which each
order of Evolution affords. The most we can hope is to establish a
qualitative correlation that is indefinitely quantitative—quantitative
in so far as involving something like a due proportion between causes
and effects. If this can be done, however, some progress will be made
towards the solution of our problem. Though it may be beyond our power
to show a measurable relation between the force or group of forces which
any phase of Evolution displays, and the force or group of forces
immediately succeeding it; yet if we can show that there always are
antecedent forces, and that the effects they produce always become the
antecedents of further ones—if while unable to calculate how much of
each change will be produced, we can prove that a change of that kind
was necessitated—if we can discern even the vaguest correspondence
between the amount of such change and the amount of the pre-existing
force; we shall advance a step towards interpreting the transformation
of the simple into the complex.
With the view of attempting this, let us now reconsider the different
types of Evolution awhile since delineated: taking them in the same
order as before.
* * * * *
§ 79. On contemplating our Solar System the first fact which strikes us,
is, that all its members are in motion; and that their motion is of a
two-fold, or rather of a three-fold, kind. Each planet and satellite has
a movement of rotation and a movement of translation; besides the
movement through space which all have in common with their rotating
primary. Whence this unceasing change of place?
The hypothesis of Evolution supplies us with an answer. Impossible as it
is to assign a reason for the pre-existence of matter in the diffused
form supposed; yet assuming its pre-existence in that form, we have in
the gravitation of its parts a cause of motion adequate to the results.
So far too as the evidence carries us, we can perceive some quantitative
relation between the motions produced, and the gravitative forces
expended in producing them. The planets formed from that matter which
has travelled the shortest distance towards the common centre of
gravity, have the smallest velocities: the uniform law being that in
advancing from the outermost to the innermost planets, the rate of
orbital motion progressively increases. It may indeed be remarked that
this is explicable on the teleological hypothesis; since it is a
condition to equilibrium. But without dwelling on the fact that this is
beside the question, it will suffice to point out that the like cannot
be said of the planetary rotations. No such final cause can be assigned
for the rapid axial movement of Jupiter and Saturn, or the slow axial
movement of Mercury. But if in pursuance of the doctrine of correlation
we look for the antecedents of these gyrations which all planets
exhibit, the theory of Evolution furnishes us with equivalent ones; and
ones which bear manifest quantitative relations to the motions
displayed. For the planets that turn on their axes with extreme
rapidity, are those having great masses and large orbits—those, that is,
of which the once diffused elements moved to their centres of gravity
through immense spaces, and so acquired high velocities. While,
conversely, there has resulted the smallest axial movement where the
orbit and the mass are both the smallest.
“But what,” it may be asked, “has in such case become of all that motion
which brought about the aggregation of this diffused matter into solid
bodies?” The rotation of each body can be but a residuary result of
concentration—a result due to the imperfect balancing of gravitative
movements from opposite points towards the common centre. Such
gravitative movements from opposite points must in great measure destroy
each other. What then has become of these mutually-destroyed motions?
The answer which the doctrine of correlation suggests is—they must have
been radiated in the form of heat and light. And this answer the
evidence, so far as it goes, confirms. Apart from any speculation
respecting the genesis of the solar system, the inquiries of geologists
lead to the conclusion that the heat of the Earth’s still molten nucleus
is but a remnant of the heat which once made molten the entire Earth.
The mountainous surfaces of the Moon and of Venus (which alone are near
enough to be scrutinized), indicating, as they do, crusts that have,
like our own, been corrugated by contraction, imply that these bodies
too have undergone refrigeration—imply in each of them a primitive heat,
such as the hypothesis necessitates. Lastly, we have in the Sun a
still-continued production of this heat and light, which must result
from the arrest of diffused matter moving towards a common centre of
gravity. Here also, as before, a quantitative relation is
traceable. Among the bodies which make up the Solar System, those
containing comparatively small amounts of matter whose centripetal
motion has been destroyed, have already lost nearly all the produced
heat: a result which their relatively larger surfaces have facilitated.
But the Sun, a thousand times as great in mass as the largest planet,
and having therefore to give off an enormously greater quantity of heat
and light due to arrest of moving matter, is still radiating with great
intensity.
Thus we see that when, in pursuance of the doctrine of correlation, we
ask whence come the forces which our Solar System displays, the
hypothesis of Evolution gives us a proximate explanation. If the Solar
System once existed in a state of indefinite, incoherent homogeneity,
and has progressed to its present state of definite, coherent
heterogeneity; then the Motion, Heat, and Light now exhibited by its
members, are interpretable as the correlatives of pre-existing forces;
and between them and their antecedents we may discern relations that are
not only qualitative, but also rudely quantitative. How matter came to
exist under the form assumed, is a mystery which we must regard as
ultimate. But grant such a previous form of existence, and the
hypothesis of Evolution interpreted by the laws of correlation, explains
for us the forces as we now see them.
* * * * *
§ 80. If we inquire the origin of those forces which have wrought the
surface of our planet into its present shape, we find them traceable to
the same primordial source as that just assigned. Assuming the solar
system to have been evolved, then geologic changes are either direct or
indirect results of the unexpended heat caused by nebular condensation.
These changes are commonly divided into igneous and aqueous:—heads under
which we may most conveniently consider them.
All those periodic disturbances which we call earthquakes, all those
elevations and subsidences which they severally produce, all those
accumulated effects of many such elevations and subsidences exhibited in
ocean-basins, islands, continents, table-lands, mountain-chains, and all
those formations which are distinguished as volcanic, geologists now
regard as modifications of the Earth’s crust produced by the
still-molten matter occupying its interior. However untenable may be the
details of M. Elie de Beaumont’s theory, there is good reason to accept
the general proposition that the disruptions and variations of level
which take place at intervals on the terrestrial surface, are due to the
progressive collapse of the Earth’s solid envelope upon its cooling and
contracting nucleus. Even supposing that volcanic eruptions, extrusions
of igneous rock, and upheaved mountain-chains, could be otherwise
satisfactorily accounted for, which they cannot; it would be impossible
otherwise to account for those wide-spread elevations and depressions
whence continents and oceans result. The conclusion to be drawn is,
then, that the forces displayed in these so-called igneous changes, are
derived positively or negatively from the unexpended heat of the Earth’s
interior. Such phenomena as the fusion or agglutination of sedimentary
deposits, the warming of springs, the sublimation of metals into the
fissures where we find them as ores, may be regarded as positive results
of this residuary heat; while fractures of strata and alterations of
level are its negative results, since they ensue on its escape. The
original cause of all these effects is still, however, as it has been
from the first, the gravitating movement of the Earth’s matter towards
the Earth’s centre; seeing that to this is due both the internal heat
itself and the collapse which takes place as it is radiated into space.
When we inquire under what forms previously existed the force which
works out the geological changes classed as aqueous, the answer is less
obvious. The effects of rain, of rivers, of winds, of waves, of marine
currents, do not manifestly proceed from one general source. Analysis,
nevertheless, proves to us that they have a common genesis. If we
ask,—Whence comes the power of the river-current, bearing sediment down
to the sea? the reply is,—The gravitation of water throughout the tract
which this river drains. If we ask,—How came the water to be dispersed
over this tract? the reply is,—It fell in the shape of rain. If we
ask,—How came the rain to be in that position whence it fell? the reply
is,—The vapour from which it was condensed was drifted there by the
winds. If we ask,—How came this vapour to be at that elevation? the
reply is,—It was raised by evaporation. And if we ask,—What force thus
raised it? the reply is,—The sun’s heat. Just that amount of gravitative
force which the sun’s heat overcame in raising the atoms of water, is
given out again in the fall of those atoms to the same level. Hence the
denudations effected by rain and rivers, during the descent of this
condensed vapour to the level of the sea, are indirectly due to the
sun’s heat. Similarly with the winds that transport the vapours hither
and thither. Consequent as atmospheric currents are on differences of
temperature (either general, as between the equatorial and polar
regions, or special as between tracts of the Earth’s surface of unlike
physical characters) all such currents are due to that source from which
the varying quantities of heat proceed. And if the winds thus originate,
so too do the waves raised by them on the sea’s surface. Whence it
follows that whatever changes waves produce—the wearing away of shores,
the breaking down of rocks into shingle, sand, and mud—are also
traceable to the solar rays as their primary cause. The same may be said
of ocean-currents. Generated as the larger ones are by the excess of
heat which the ocean in tropical climates continually acquires from the
Sun; and generated as the smaller ones are by minor local differences in
the quantities of solar heat absorbed; it follows that the distribution
of sediment and other geological processes which these marine currents
effect, are affiliable upon the force which the sun radiates. The only
aqueous agency otherwise originating is that of the tides—an agency
which, equally with the others, is traceable to unexpended astronomical
motion. But making allowance for the changes which this works, we reach
the conclusion that the slow wearing down of continents and gradual
filling up of seas, by rain, rivers, winds, waves, and ocean-streams,
are the indirect effects of solar heat.
Thus the implication forced on us by the doctrine of correlation, that
the forces which have moulded and re-moulded the Earth’s crust must have
pre-existed under some other shape, is quite in conformity with the
theory of Evolution; since this pre-supposes certain forces that are
both adequate to the results, and cannot be expended without producing
the results. We see that while the geological changes classed as
igneous, result from the still-progressing motion of the Earth’s
substance to its centre of gravity; the antagonistic changes classed as
aqueous, result from the still-progressing motion of the Sun’s substance
towards its centre of gravity—a motion which, transformed into heat and
radiated to us, is here re-transformed, directly into motions of the
gaseous and liquid matters on the Earth’s surface, and indirectly into
motions of the solid matters.
* * * * *
§ 81. That the forces exhibited in vital actions, vegetal and animal,
are similarly derived, is so obvious a deduction from the facts of
organic chemistry, that it will meet with ready acceptance from readers
acquainted with these facts. Let us note first the physiological
generalizations; and then the generalizations which they necessitate.
Plant-life is all directly or indirectly dependant on the heat and light
of the sun—directly dependant in the immense majority of plants, and
indirectly dependant in plants which, as the fungi, flourish in the
dark: since these, growing as they do at the expense of decaying organic
matter, mediately draw their forces from the same original source. Each
plant owes the carbon and hydrogen of which it mainly consists, to the
carbonic acid and water contained in the surrounding air and earth. The
carbonic acid and water must, however, be decomposed before their carbon
and hydrogen can be assimilated. To overcome the powerful affinities
which hold their elements together, requires the expenditure of force;
and this force is supplied by the Sun. In what manner the decomposition
is effected we do not know. But we know that when, under fit conditions,
plants are exposed to the Sun’s rays, they give off oxygen and
accumulate carbon and hydrogen. In darkness this process ceases. It
ceases too when the quantities of light and heat received are greatly
reduced, as in winter. Conversely, it is active when the light and heat
are great, as in summer. And the like relation is seen in the fact that
while plant-life is luxuriant in the tropics, it diminishes in temperate
regions, and disappears as we approach the poles. Thus the irresistible
inference is, that the forces by which plants abstract the materials of
their tissues from surrounding inorganic compounds—the forces by which
they grow and carry on their functions, are forces that previously
existed as solar radiations.
That animal life is immediately or mediately dependant on vegetal life
is a familiar truth; and that, in the main, the processes of animal life
are opposite to those of vegetal life is a truth long current among men
of science. Chemically considered, vegetal life is chiefly a process of
de-oxidation, and animal life chiefly a process of oxidation: chiefly,
we must say, because in so far as plants are expenders of force for the
purposes of organization, they are oxidizers (as is shown by the
exhalation of carbonic acid during the night); and animals, in some of
their minor processes, are probably de-oxidizers. But with this
qualification, the general truth is that while the plant, decomposing
carbonic acid and water and liberating oxygen, builds up the detained
carbon and hydrogen (along with a little nitrogen and small quantities
of other elements elsewhere obtained) into branches, leaves, and seeds;
the animal, consuming these branches, leaves, and seeds, and absorbing
oxygen, recomposes carbonic acid and water, together with certain
nitrogenous compounds in minor amounts. And while the decomposition
effected by the plant, is at the expense of certain forces emanating
from the sun, which are employed in overcoming the affinities of carbon
and hydrogen for the oxygen united with them; the recomposition effected
by the animal, is at the profit of these forces, which are liberated
during the combination of such elements. Thus the movements, internal
and external, of the animal, are re-appearances in new forms of a power
absorbed by the plant under the shape of light and heat. Just as, in the
manner above explained, the solar forces expended in raising vapour from
the sea’s surface, are given out again in the fall of rain and rivers to
the same level, and in the accompanying transfer of solid matters; so,
the solar forces that in the plant raised certain chemical elements to a
condition of unstable equilibrium, are given out again in the actions of
the animal during the fall of these elements to a condition of stable
equilibrium.
Besides thus tracing a qualitative correlation between these two great
orders of organic activity, as well as between both of them and
inorganic agencies, we may rudely trace a quantitative correlation.
Where vegetal life is abundant, we usually find abundant animal life;
and as we advance from torrid to temperate and frigid climates, the two
decrease together. Speaking generally, the animals of each class reach a
larger size in regions where vegetation is abundant, than in those where
it is sparse. And further, there is a tolerably apparent connexion
between the quantity of energy which each species of animal expends, and
the quantity of force which the nutriment it absorbs gives out during
oxidation.
Certain phenomena of development in both plants and animals, illustrate
still more directly the ultimate truth enunciated. Pursuing the
suggestion made by Mr. Grove, in the first edition of his work on the
“Correlation of the Physical Forces,” that a connexion probably exists
between the forces classed as vital and those classed as physical, Dr.
Carpenter has pointed out that such a connexion is clearly exhibited
during incubation. The transformation of the unorganized contents of an
egg into the organized chick, is altogether a question of heat: withhold
heat and the process does not commence; supply heat and it goes on while
the temperature is maintained, but ceases when the egg is allowed to
cool. The developmental changes can be completed only by keeping the
temperature with tolerable constancy at a definite height for a definite
time; that is—only by supplying a definite quantity of heat. In the
metamorphoses of insects we may discern parallel facts. Experiments show
not only that the hatching of their eggs is determined by temperature,
but also that the evolution of the pupa into the imago is similarly
determined; and may be immensely accelerated or retarded according as
heat is artificially supplied or withheld. It will suffice just to add
that the germination of plants presents like relations of cause and
effect—relations so similar that detail is superfluous.
Thus then the various changes exhibited to us by the organic creation,
whether considered as a whole, or in its two great divisions, or in its
individual members, conform, so far as we can ascertain, to the law of
correlation. Where, as in the transformation of an egg into a chick, we
can investigate the phenomena apart from all complications, we find that
the re-arrangement of parts which constitutes evolution, involves
expenditure of a pre-existing force. Where it is not, as in the egg or
the chrysalis, merely the change of a fixed quantity of matter into a
new shape, but where, as in the growing plant or animal, we have an
incorporation of matter existing outside, there is still a pre-existing
external force at the cost of which this incorporation is effected. And
where, as in the higher division of organisms, there remain over and
above the forces expended in organization, certain surplus forces
expended in movement, these too are indirectly derived from this same
pre-existing external force.
* * * * *
§ 82. Even after all that has been said in the foregoing part of this
work, many will be alarmed by the assertion, that the forces which we
distinguish as mental, come within the same generalization. Yet there is
no alternative but to make this assertion: the facts which justify, or
rather which necessitate it, being abundant and conspicuous. They fall
into the following groups.
All impressions from moment to moment made on our organs of sense, stand
in direct correlation with physical forces existing externally. The
modes of consciousness called pressure, motion, sound, light, heat, are
effects produced in us by agencies which, as otherwise expended, crush
or fracture pieces of matter, generate vibrations in surrounding
objects, cause chemical combinations, and reduce substances from a solid
to a liquid form. Hence if we regard the changes of relative position,
of aggregation, or of chemical state, thus arising, as being transformed
manifestations of the agencies from which they arise; so must we regard
the sensations which such agencies produce in us, as new forms of the
forces producing them. Any hesitation to admit that, between the
physical forces and the sensations there exists a correlation like that
between the physical forces themselves, must disappear on remembering
how the one correlation, like the other, is not qualitative only but
quantitative. Masses of matter which, by scales or dynamometer, are
shown to differ greatly in weight, differ as greatly in the feelings of
pressure they produce on our bodies. In arresting moving objects, the
strains we are conscious of are proportionate to the momenta of such
objects as otherwise measured. Under like conditions the impressions of
sounds given to us by vibrating strings, bells, or columns of air, are
found to vary in strength with the amount of force applied. Fluids or
solids proved to be markedly contrasted in temperature by the different
degrees of expansion they produce in the mercurial column, produce in us
correspondingly different degrees of the sensation of heat. And
similarly unlike intensities in our impressions of light, answer to
unlike effects as measured by photometers.
Besides the correlation and equivalence between external physical
forces, and the mental forces generated by them in us under the form of
sensations, there is a correlation and equivalence between sensations
and those physical forces which, in the shape of bodily actions, result
from them. The feelings we distinguish as light, heat, sound, odour,
taste, pressure, &.c, do not die away without immediate results; but are
invariably followed by other manifestations of force. In addition to the
excitements of secreting organs, that are in some cases traceable, there
arises a contraction of the involuntary muscles, or of the voluntary
muscles, or of both. Sensations increase the action of the
heart—slightly when they are slight; markedly when they are marked; and
recent physiological inquiries imply not only that contraction of the
heart is excited by every sensation, but also that the muscular fibres
throughout the whole, vascular system, are at the same time more or less
contracted. The respiratory muscles, too, are stimulated into greater
activity by sensations. The rate of breathing is visibly and audibly
augmented both by pleasurable and painful impressions on the nerves,
when these reach any intensity. It has even of late been shown that
inspiration becomes more frequent on transition from darkness into
sunshine,—a result probably due to the increased amount of direct and
indirect nervous stimulation involved. When the quantity of sensation is
great, it generates contractions of the voluntary muscles, as well as of
the involuntary ones. Unusual excitement of the nerves of touch, as by
tickling, is followed by almost incontrollable movements of the limbs.
Violent pains cause violent struggles. The start that succeeds a loud
sound, the wry face produced by the taste of anything extremely
disagreeable, the jerk with which the hand or foot is snatched out of
water that is very hot, are instances of the transformation of feeling:
into motion; and in these cases, as in all others, it is manifest that
the quantity of bodily action is proportionate to the quantity of
sensation. Even where from pride there is a suppression of the screams
and groans expressive of great pain (also indirect results of muscular
contraction), we may still see in the clenching of the hands, the
knitting of the brows, and the setting of the teeth, that the bodily
actions developed are as great, though less obtrusive in their results.
If we take emotions instead of sensations, we find the correlation
and equivalence equally manifest. Not only are the modes of
consciousness directly produced in us by physical forces,
re-transformable into physical forces under the form of muscular motions
and the changes they initiate; but the like is true of those modes of
consciousness which are not directly produced in us by the physical
forces. Emotions of moderate intensity, like sensations of moderate
intensity, generate little beyond excitement of the heart and vascular
system, joined sometimes with increased action of glandular organs. But
as the emotions rise in strength, the muscles of the face, body, and
limbs, begin to move. Of examples may be mentioned the frowns, dilated
nostrils, and stampings of anger; the contracted brows, and wrung hands,
of grief; the smiles and leaps of joy; and the frantic struggles of
terror or despair. Passing over certain apparent, but only apparent,
exceptions, we see that whatever be the kind of emotion, there is a
manifest relation between its amount, and the amount of muscular action
induced: alike from the erect carriage and elastic step of exhilaration,
up to the dancings of immense delight, and from the fidgetiness of
impatience up to the almost convulsive movements accompanying great
mental agony. To these several orders of evidence must be joined
the further one, that between our feelings and those voluntary motions
into which they are transformed, there comes the sensation of muscular
tension, standing in manifest correlation with both—a correlation that
is distinctly quantitative: the sense of strain varying, other things
equal, directly as the quantity of momentum generated.
“But how,” it may be asked, “can we interpret by the law of correlation
the genesis of those thoughts and feelings which, instead of following
external stimuli, arise spontaneously? Between the indignation caused by
an insult, and the loud sounds or violent acts that follow, the alleged
connexion may hold; but whence come the crowd of ideas and the mass of
feelings that expend themselves in these demonstrations? They are
clearly not equivalents of the sensations produced by the words on the
ears; for the same words otherwise arranged, would not have caused them.
The thing said bears to the mental action it excites, much the same
relation that the pulling of a trigger bears to the subsequent
explosion—does not produce the power, but merely liberates it. Whence
then arises this immense amount of nervous energy which a whisper or a
glance may call forth?” The reply is, that the immediate
correlates of these and other such modes of consciousness, are not to be
found in the agencies acting on us externally, but in certain internal
agencies. The forces called vital, which we have seen to be correlates
of the forces called physical, are the immediate sources of these
thoughts and feelings; and are expended in producing them. The proofs of
this are various. Here are some of them. It is a conspicuous fact
that mental action is contingent on the presence of a certain nervous
apparatus; and that, greatly obscured as it is by numerous and involved
conditions, a general relation may be traced between the size of this
apparatus and the quantity of mental action as measured by its results.
Further, this apparatus has a particular chemical constitution on which
its activity depends; and there is one element in it between the amount
of which and the amount of function performed, there is an ascertained
connexion: the proportion of phosphorus present in the brain being the
smallest in infancy, old age and idiotcy, and the greatest during the
prime of life. Note next, that the evolution of thought and
emotion varies, other things equal, with the supply of blood to the
brain. On the one hand, a cessation of the cerebral circulation, from
arrest of the heart’s action, immediately entails unconsciousness. On
the other hand, excess of cerebral circulation (unless it is such as to
cause undue pressure) results in an excitement rising finally to
delirium. Not the quantity only, but also the condition of the
blood passing through the nervous system, influences the mental
manifestations. The arterial currents must be duly aerated, to produce
the normal amount of cerebration. At the one extreme, we find that if
the blood is not allowed to exchange its carbonic acid for oxygen, there
results asphyxia, with its accompanying stoppage of ideas and feelings.
While at the other extreme, we find that by the inspiration of nitrous
oxide, there is produced an excessive, and indeed irrepressible, nervous
activity. Besides the connexion between the development of the
mental forces and the presence of sufficient oxygen in the cerebral
arteries, there is a kindred connexion between the development of the
mental forces and the presence in the cerebral arteries of certain other
elements. There must be supplied special materials for the nutrition of
the nervous centres, as well as for their oxidation. And how what we may
call the quantity of consciousness, is, other things equal, determined
by the constituents of the blood, is unmistakably seen in the exaltation
that follows when certain chemical compounds, as alcohol and the
vegeto-alkalies, are added to it. The gentle exhilaration which tea and
coffee create, is familiar to all; and though the gorgeous imaginations
and intense feelings of happiness produced by opium and hashish, have
been experienced by few, (in this country at least,) the testimony of
those who have experienced them is sufficiently conclusive. Yet
another proof that the genesis of the mental energies is immediately
dependent on chemical change, is afforded by the fact, that the effete
products separated from the blood by the kidneys, vary in character with
the amount of cerebral action. Excessive activity of mind is habitually
accompanied by the excretion of an unusual quantity of the alkaline
phosphates. Conditions of abnormal nervous excitement bring on analogous
effects. And the “peculiar odour of the insane,” implying as it does
morbid products in the perspiration, shows a connexion between insanity
and a special composition of the circulating fluids—a composition which,
whether regarded as cause or consequence, equally implies correlation of
the mental and the physical forces. Lastly we have to note that
this correlation too, is, so far as we can trace it, quantitative.
Provided the conditions to nervous action are not infringed on, and the
concomitants are the same, there is a tolerably constant ratio between
the amounts of the antecedents and consequents. Within the implied
limits, nervous stimulants and anæsthetics produce effects on the
thoughts and feelings, proportionate to the quantities administered. And
conversely, where the thoughts and feelings form the initial term of the
relation, the degree of reaction on the bodily energies is great, in
proportion as they are great: reaching in extreme cases a total
prostration of physique.
Various classes of facts thus unite to prove that the law of
metamorphosis, which holds among the physical forces, holds equally
between them and the mental forces. Those modes of the Unknowable which
we call motion, heat, light, chemical affinity, &c., are alike
transformable into each other, and into those modes of the Unknowable
which we distinguish as sensation, emotion, thought: these, in their
turns, being directly or indirectly re-transformable into the original
shapes. That no idea or feeling arises, save as a result of some
physical force expended in producing it, is fast becoming a common place
of science; and whoever duly weighs the evidence will see, that nothing
but an overwhelming bias in favour of a pre-conceived theory, can
explain its non-acceptance. How this metamorphosis takes place—how
a force existing as motion, heat, or light, can become a mode of
consciousness—how it is possible for aerial vibrations to generate the
sensation we call sound, or for the forces liberated by chemical changes
in the brain to give rise to emotion—these are mysteries which it is
impossible to fathom. But they are not profounder mysteries than the
transformations of the physical forces into each other. They are not
more completely beyond our comprehension than the natures of Mind and
Matter. They have simply the same insolubility as all other ultimate
questions. We can learn nothing more than that here is one of the
uniformities in the order of phenomena.
* * * * *
§ 83. Of course if the law of correlation and equivalence holds of the
forces we class as vital and mental, it must hold also of those which we
class as social. Whatever takes place in a society is due to organic or
inorganic agencies, or to a combination of the two—results either from
the undirected physical forces around, from these physical forces as
directed by men, or from the forces of the men themselves. No change can
occur in its organization, its modes of activity, or the effects it
produces on the face of the Earth, but what proceeds, mediately or
immediately, from these. Let us consider first the correlation between
the phenomena which societies display, and the vital phenomena.
Social power and life varies, other things equal, with the population.
Though different races, differing widely in their fitness for
combination, show us that the forces manifested in a society are not
necessarily proportionate to the number of people; yet we see that under
given conditions, the forces manifested are confined within the limits
which the number of people imposes. A small society, no matter how
superior the character of its members, cannot exhibit the same quantity
of social action as a large one. The production and distribution of
commodities must be on a comparatively small scale. A multitudinous
press, a prolific literature, or a massive political agitation, is not
possible. And there can be but a small total of results in the shape of
art-products and scientific discoveries. The correlation of the
social with the physical forces through the intermediation of the vital
ones, is, however, most clearly shown in the different amounts of
activity displayed by the same society according as its members are
supplied with different amounts of force from the external world. In the
effects of good and bad harvests, we yearly see this relation
illustrated. A greatly deficient yield of wheat is soon followed by a
diminution of business. Factories are worked half-time, or close
entirely; railway traffic falls; retailers find their sales much
lessened; house-building is almost suspended; and if the scarcity rises
to famine, a thinning of the population still more diminishes the
industrial vivacity. Conversely, an unusually abundant harvest,
occurring under conditions not otherwise unfavourable, both excites the
old producing and distributing agencies and sets up new ones. The
surplus social energy finds vent in speculative enterprises. Capital
seeking investment carries out inventions that have been lying
unutilized. Labour is expended in opening new channels of communication.
There is increased encouragement to those who furnish the luxuries of
life and minister to the æsthetic faculties. There are more marriages,
and a greater rate of increase in population. Thus the social organism
grows larger, more complex, and more active. When, as happens with
most civilized nations, the whole of the materials for subsistence are
not drawn from the area inhabited, but are partly imported, the people
are still supported by certain harvests elsewhere grown at the expense
of certain physical forces. Our own cotton-spinners and weavers supply
the most conspicuous instance of a section in one nation living, in
great part, on imported commodities, purchased by the labour they expend
on other imported commodities. But though the social activities of
Lancashire are due chiefly to materials not drawn from our own soil,
they are none the less evolved from physical forces elsewhere stored up
in fit forms and then brought here.
If we ask whence come these physical forces from which, through the
intermediation of the vital forces, the social forces arise, the reply
is of course as heretofore—the solar radiations. Based as the life of a
society is on animal and vegetal products; and dependent as these animal
and vegetal products are on the light and heat of the sun; it follows
that the changes going on in societies are effects of forces having a
common origin with those which produce all the other orders of changes
that have been analyzed. Not only is the force expended by the horse
harnessed to the plough, and by the labourer guiding it, derived from
the same reservoir as is the force of the falling cataract and the
roaring hurricane; but to this same reservoir are eventually traceable
those subtler and more complex manifestations of force which humanity,
as socially embodied, evolves. The assertion is a startling one, and by
many will be thought ludicrous; but it is an unavoidable deduction which
cannot here be passed over.
Of the physical forces that are directly transformed into social ones,
the like is to be said. Currents of air and water, which before the use
of steam were the only agencies brought in aid of muscular effort for
the performance of industrial processes, are, as we have seen, generated
by the heat of the sun. And the inanimate power that now, to so vast an
extent, supplements human labour, is similarly derived. The late George
Stephenson was one of the first to recognize the fact that the force
impelling his locomotive, originally emanated from the sun. Step by step
we go back—from the motion of the piston to the evaporation of the
water; thence to the heat evolved during the oxidation of coal; thence
to the assimilation of carbon by the plants of whose imbedded remains
coal consists; thence to the carbonic acid from which their carbon was
obtained; and thence to the rays of light that de-oxidized this carbonic
acid. Solar forces millions of years ago expended on the Earth’s
vegetation, and since locked up beneath its surface, now smelt the
metals required for our machines, turn the lathes by which the machines
are shaped, work them when put together, and distribute the fabrics they
produce. And in so far as economy of labour makes possible the support
of a larger population; gives a surplus of human power that would else
be absorbed in manual occupations; and so facilitates the development of
higher kinds of activity; it is clear that these social forces which are
directly correlated with physical forces anciently derived from the sun,
are only less important than those whose correlates are the vital forces
recently derived from it.
* * * * *
§ 84. Regarded as an induction, the doctrine set forth in this chapter
will most likely be met by a demurrer. Many who admit that among
physical phenomena at least, the correlation of forces is now
established, will probably say that inquiry has not yet gone far enough
to enable us to predicate equivalence. And in respect of the forces
classed as vital, mental, and social, the evidence assigned, however
little to be explained away, they will consider by no means conclusive
even of correlation, much less of equivalence.
To those who think thus, it must now however be pointed out, that the
universal truth above illustrated under its various aspects, is a
necessary corollary from the persistence of force. Setting out with the
proposition that force can neither come into existence, nor cease to
exist, the several foregoing general conclusions inevitably follow. Each
manifestation of force can be interpreted only as the effect of some
antecedent force: no matter whether it be an inorganic action, an animal
movement, a thought, or a feeling. Either this must be conceded, or else
it must be asserted that our successive states of consciousness are
self-created. Either mental energies, as well as bodily ones, are
quantitatively correlated to certain energies expended in their
production, and to certain other energies which they initiate; or else
nothing must become something and something must become nothing. The
alternatives are, to deny the persistence of force, or to admit that
every physical and psychial change is generated by certain antecedent
forces, and that from given amounts of such forces neither more nor less
of such physical and psychial changes can result. And since the
persistence of force, being a datum of consciousness, cannot be denied,
its unavoidable corollary must be accepted. This corollary cannot
indeed be made more certain by accumulating illustrations. The truth as
arrived at deductively, cannot be inductively confirmed. For every one
of such facts as those above detailed, is established only through the
indirect assumption of that persistence of force, from which it really
follows as a direct consequence. The most exact proof of correlation and
equivalence which it is possible to reach by experimental inquiry, is
that based on measurement of the forces expended and the forces
produced. But, as was shown in the last chapter, any such process of
measurement implies the use of some unit of force which is assumed to
remain constant; and for this assumption there can be no warrant but
that it is a corollary from the persistence of force. How then can any
reasoning based on this corollary, prove the equally direct corollary
that when a given quantity of force ceases to exist under one form, an
equal quantity must come into existence under some other form or forms?
Clearly the _à priori_ truth expressed in this last corollary, cannot be
more firmly established by any _à posteriori_ proofs which the first
corollary helps us to.
“What then,” it may be asked, “is the use of these investigations by
which the correlation and equivalence of forces is sought to be
established as an inductive truth? Surely it will not be alleged that
they are useless. Yet if this correlation cannot be made more certain by
them than it is already, does not their uselessness necessarily follow?”
No. They are of value as disclosing the many particular implications
which the general truth does not specify. They are of value as teaching
us how much of one mode of force is the equivalent of so much of another
mode. They are of value as determining under what conditions each
metamorphosis occurs. And they are of value as leading us to inquire in
what shape the remnant of force has escaped, when the apparent results
are not equivalent to the cause.