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.




                               CHAPTER X.
                        THE DIRECTION OF MOTION.


§ 85. The Absolute Cause of changes, inclusive of those constituting
Evolution, is not less incomprehensible in respect of the unity or
duality of its action, than in all other respects. We cannot decide
between the alternative suppositions, that phenomena are due to the
variously-conditioned workings of a single force, and that they are due
to the conflict of two forces. Whether, as some contend, everything is
explicable on the hypothesis of universal pressure, whence what we call
tension results differentially from inequalities of pressure in opposite
directions; or whether, as might be with equal propriety contended,
things are to be explained on the hypothesis of universal tension, from
which pressure is a differential result; or whether, as most physicists
hold, pressure and tension everywhere co-exist; are questions which it
is impossible to settle. Each of these three suppositions makes the
facts comprehensible, only by postulating an inconceivability. To assume
a universal pressure, confessedly requires us to assume an infinite
plenum�an unlimited space full of something which is everywhere pressed
by something beyond; and this assumption cannot be mentally realized.
That universal tension is the immediate agency to which phenomena are
due, is an idea open to a parallel and equally fatal objection. And
however verbally intelligible may be the proposition that pressure and
tension everywhere co-exist, yet we cannot truly represent to ourselves
one ultimate unit of matter as drawing another while resisting it.

Nevertheless, this last belief is one which we are compelled to
entertain. Matter cannot be conceived except as manifesting forces of
attraction and repulsion. Body is distinguished in our consciousness
from Space, by its opposition to our muscular energies; and this
opposition we feel under the two-fold form of a cohesion that hinders
our efforts to rend, and a resistance that hinders our efforts to
compress. Without resistance there can be merely empty extension.
Without cohesion there can be no resistance. Probably this conception of
antagonistic forces, is originally derived from the antagonism of our
flexor and extensor muscles. But be this as it may, we are obliged to
think of all objects as made up of parts that attract and repel each
other; since this is the form of our experience of all objects.

By a higher abstraction results the conception of attractive and
repulsive forces pervading space. We cannot dissociate force from
occupied extension, or occupied extension from force; because we have
never an immediate consciousness of either in the absence of the other.
Nevertheless, we have abundant proof that force is exercised through
what appears to our senses a vacuity. Mentally to represent this
exercise, we are hence obliged to fill the apparent vacuity with a
species of matter�an etherial medium. The constitution we assign to this
etherial medium, however, like the constitution we assign to solid
substance, is necessarily an abstract of the impressions received from
tangible bodies. The opposition to pressure which a tangible body offers
to us, is not shown in one direction only, but in all directions; and so
likewise is its tenacity. Suppose countless lines radiating from its
centre on every side, and it resists along each of these lines and
coheres along each of these lines. Hence the constitution of those
ultimate units through the instrumentality of which phenomena are
interpreted. Be they atoms of ponderable matter or molecules of ether,
the properties we conceive them to possess are nothing else than these
perceptible properties idealized. Centres of force attracting and
repelling each other in all directions, are simply insensible portions
of matter having the endowments common to sensible portions of
matter�endowments of which we cannot by any mental effort divest them.
In brief, they are the invariable elements of the conception of matter,
abstracted from its variable elements�size, form, quality, &c. And so to
interpret manifestations of force which cannot be tactually experienced,
we use the terms of thought supplied by our tactual experiences; and
this for the sufficient reason that we must use these or none.

After all that has been before shown, and after the hint given above, it
needs scarcely be said that these universally co-existent forces of
attraction and repulsion, must not be taken as realities, but as our
symbols of the reality. They are the forms under which the workings of
the Unknowable are cognizable by us�modes of the Unconditioned as
presented under the conditions of our consciousness. But while knowing
that the ideas thus generated in us are not absolutely true, we may
unreservedly surrender ourselves to them as relatively true; and may
proceed to evolve a series of deductions having a like relative truth.

                  *       *       *       *       *

§ 86. From universally co-existent forces of attraction and repulsion,
there result certain laws of direction of all movement. Where attractive
forces alone are concerned, or rather are alone appreciable, movement
takes place in the direction of their resultant; which may, in a sense,
be called the line of greatest traction. Where repulsive forces alone
are concerned, or rather are alone appreciable, movement takes place
along their resultant; which is usually known as the line of least
resistance. And where both attractive and repulsive forces are
concerned, or are appreciable, movement takes place along the resultant
of all the tractions and resistances. Strictly speaking, this last is
the sole law; since, by the hypothesis, both forces are everywhere in
action. But very frequently the one kind of force is so immensely in
excess that the effect of the other kind may be left out of
consideration. Practically we may say that a body falling to the Earth,
follows the line of greatest traction; since, though the resistance of
the air must, if the body be irregular, cause some divergence from this
line, (quite perceptible with feathers and leaves,) yet ordinarily the
divergence is so slight that we may omit it. In the same manner, though
the course taken by the steam from an exploding boiler, differs somewhat
from that which it would take were gravitation out of the question; yet,
as gravitation affects its course infinitesimally, we are justified in
asserting that the escaping steam follows the line of least resistance.
Motion then, we may say, always follows the line of greatest traction,
or the line of least resistance, or the resultant of the two: bearing in
mind that though the last is alone strictly true, the others are in many
cases sufficiently near the truth for practical purposes.

Movement set up in any direction is itself a cause of further movement
in that direction, since it is the embodiment of a surplus force in that
direction. This holds equally with the transit of matter through space,
the transit of matter through matter, and the transit through matter of
any kind of vibration. In the case of matter moving through space, this
principle is expressed in the law of inertia�a law on which the
calculations of physical astronomy are wholly based. In the case of
matter moving through matter, we trace the same truth under the familiar
experience that any breach made by one solid through another, or any
channel formed by a fluid through a solid, becomes a route along which,
other things equal, subsequent movements of like nature take place. And
in the case of motion passing through matter under the form of an
impulse communicated from part to part, the facts of magnetization go to
show that the establishment of undulations along certain lines,
determines their continuance along those lines.

It further follows from the conditions, that the direction of movement
can rarely if ever be perfectly straight. For matter in motion to pursue
continuously the exact line in which it sets out, the forces of
attraction and repulsion must be symmetrically disposed around its path;
and the chances against this are infinitely great. The impossibility of
making an absolutely true edge to a bar of metal�the fact that all which
can be done by the best mechanical appliances, is to reduce the
irregularities of such an edge to amounts that cannot be perceived
without magnifiers�sufficiently exemplifies how, in consequence of the
unsymmetrical distribution of forces around the line of movement, the
movement is rendered more or less indirect.       It may be well to add
that in proportion as the forces at work are numerous and varied, the
curve a moving body describes is necessarily complex: witness the
contrast between the flight of an arrow and the gyrations of a stick
tossed about by breakers.

We have now to trace these laws of direction of movement throughout the
process of Evolution, under its various forms. We have to note how every
change in the arrangement of parts, takes place along the line of
greatest traction, of least resistance, or of their resultant; how the
setting up of motion along a certain line, becomes a cause of its
continuance along that line; how, nevertheless, change of relations to
external forces, always renders this line indirect; and how the degree
of its indirectness increases with every addition to the number of
influences at work.

                  *       *       *       *       *

§ 87. If we assume the first stage in nebular condensation to be the
precipitation into flocculi of denser matter previously diffused through
a rarer medium, (a supposition both physically justified, and in harmony
with certain astronomical observations,) we shall find that nebular
motion is interpretable in pursuance of the above general laws. Each
portion of such vapour-like matter must begin to move towards the common
centre of gravity. The tractive forces which would of themselves carry
it in a straight line to the centre of gravity, are opposed by the
resistant forces of the medium through which it is drawn. The direction
of movement must be the resultant of these�a resultant which, in
consequence of the unsymmetrical form of the flocculus, must be a curve
directed, not to the centre of gravity, but towards one side of it. And
it may be readily shown that in an aggregation of such flocculi,
severally thus moving, there must, by composition of forces, eventually
result a rotation of the whole nebula in one direction.

Merely noting this hypothetical illustration for the purpose of showing
how the law applies to the case of nebular evolution, supposing it to
have taken place, let us pass to the phenomena of the Solar System as
now exhibited. Here the general principles above set forth are every
instant exemplified. Each planet and satellite has a momentum which
would, if acting alone, carry it forward in the direction it is at any
instant pursuing. This momentum hence acts as a resistance to motion in
any other direction. Each planet and satellite, however, is drawn by a
force which, if unopposed, would take it in a straight line towards its
primary. And the resultant of these two forces is that curve which it
describes�a curve manifestly consequent on the unsymmetrical
distribution of the forces around its path. This path, when more closely
examined, supplies us with further illustrations. For it is not an exact
circle or ellipse; which it would be were the tangential and centripetal
forces the only ones concerned. Adjacent members of the Solar System,
ever varying in their relative positions, cause what we call
perturbations; that is, slight divergences in various directions from
that circle or ellipse which the two chief forces would produce. These
perturbations severally show us in minor degrees, how the line of
movement is the resultant of all the forces engaged; and how this line
becomes more complicated in proportion as the forces are multiplied.
      If instead of the motions of the planets and satellites as wholes,
we consider the motions of their parts, we meet with comparatively
complex illustrations. Every portion of the Earth�s substance in its
daily rotation, describes a curve which is in the main a resultant of
that resistance which checks its nearer approach to the centre of
gravity, that momentum which would carry it off at a tangent, and those
forces of gravitation and cohesion which keep it from being so carried
off. If this axial motion be compounded with the orbital motion, the
course of each part is seen to be a much more involved one. And we find
it to have a still greater complication on taking into account that
lunar attraction which mainly produces the tides and the precession of
the equinoxes.

                  *       *       *       *       *

§ 88. We come next to terrestrial changes: present ones as observed, and
past ones as inferred by geologists. Let us set out with the
hourly-occurring alterations in the Earth�s atmosphere; descend to the
slower alterations in progress on its surface; and then to the still
slower ones going on beneath.

Masses of air, absorbing heat from surfaces warmed by the sun, expand,
and so lessen the weight of the atmospheric columns of which they are
parts. Hence they offer to adjacent atmospheric columns, diminished
lateral resistance; and these, moving in the directions of the
diminished resistance, displace the expanded air; while this, pursuing
an upward course, displays a motion along that line in which there is
least pressure. When again, by the ascent of such heated masses from
extended areas like the torrid zone, there is produced at the upper
surface of the atmosphere, a protuberance beyond the limits of
equilibrium�when the air forming this protuberance begins to overflow
laterally towards the poles; it does so because, while the tractive
force of the Earth is nearly the same, the lateral resistance is greatly
diminished. And throughout the course of each current thus generated, as
well as throughout the course of each counter-current flowing: into the
vacuum that is left, the direction is always the resultant of the
Earth�s tractive force and the resistance offered by the surrounding
masses of air: modified only by conflict with other currents similarly
determined, and by collision with prominences on the Earth�s crust.
      The movements of water, in both its gaseous and liquid states,
furnish further examples. In conformity with the mechanical theory of
heat, it may be shown that evaporation is the escape of particles of
water in the direction of least resistance; and that as the resistance
(which is due to the pressure of the water diffused in a gaseous state)
diminishes, the evaporation increases. Conversely, that rushing together
of particles called condensation, which takes place when any portion of
atmospheric vapour has its temperature much lowered, may be interpreted
as a diminution of the mutual pressure among the condensing particles,
while the pressure of surrounding particles remains the same; and so is
a motion taking place in the direction of lessened resistance. In the
course followed by the resulting rain-drops, we have one of the simplest
instances of the joint effect of the two antagonist forces. The Earth�s
attraction, and the resistance of atmospheric currents ever varying in
direction and intensity, give as their resultants, lines which incline
to the horizon in countless different degrees and undergo perpetual
variations. More clearly still is the law exemplified by these same
rain-drops when they reach the ground. In the course they take while
trickling over its surface, in every rill, in every larger stream, and
in every river, we see them descending as straight as the antagonism of
surrounding objects permits. From moment to moment, the motion of water
towards the Earth�s centre is opposed by the solid matter around and
under it; and from moment to moment its route is the resultant of the
lines of greatest traction and least resistance. So far from a cascade
furnishing, as it seems to do, an exception, it furnishes but another
illustration. For though all solid obstacles to a vertical fall of the
water are removed, yet the water�s horizontal momentum is an obstacle;
and the parabola in which the stream leaps from the projecting ledge, is
generated by the combined gravitation and momentum.       It may be well
just to draw attention to the degree of complexity here produced in the
line of movement by the variety of forces at work. In atmospheric
currents, and still more clearly in water-courses (to which might be
added ocean-streams), the route followed is too complex to be defined,
save as a curve of three dimensions with an ever varying equation.

The Earth�s solid crust undergoes changes that supply another group of
illustrations. The denudation of lands and the depositing of the removed
sediment in new strata at the bottoms of seas and lakes, is a process
throughout which motion is obviously determined in the same way as is
that of the water effecting the transport. Again, though we have no
direct inductive proof that the forces classed as igneous, expend
themselves along lines of least resistance; yet what little we know of
them is in harmony with the belief that they do so. Earthquakes
continually revisit the same localities, and special tracts undergo for
long periods together successive elevations or subsidences,�facts which
imply that already-fractured portions of the Earth�s crust are those
most prone to yield under the pressure caused by further contractions.
The distribution of volcanoes along certain lines, as well as the
frequent recurrence of eruptions from the same vents, are facts of like
meaning.

                  *       *       *       *       *

§ 89. That organic growth takes place in the direction of least
resistance, is a proposition that has been set forth and illustrated by
Mr. James Hinton, in the _Medico-Chirurgical Review_ for October, 1858.
After detailing a few of the early observations which led him to this
generalization, he formulates it thus:�

�Organic form is the result of motion.�

�Motion takes the direction of least resistance.�

�Therefore organic form is the result of motion in the direction of
least resistance.�

After an elucidation and defence of this position, Mr. Hinton proceeds
to interpret, in conformity with it, sundry phenomena of development.
Speaking of plants he says:�

�The formation of the root furnishes a beautiful illustration of the law
of least resistance, for it grows by insinuating itself, cell by cell,
through the interstices of the soil; it is by such minute additions that
it increases, winding and twisting whithersoever the obstacles it meets
in its path determine, and growing there most, where the nutritive
materials are added to it most abundantly. As we look on the roots of a
mighty tree, it appears to us as if they had forced themselves with
giant violence into the solid earth. But it is not so; they were led on
gently, cell added to cell, softly as the dews descended, and the
loosened earth made way. Once formed, indeed, they expand with an
enormous power, but the spongy condition of the growing radicles utterly
forbids the supposition that they are forced into the earth. Is it not
probable, indeed, that the enlargement of the roots already formed may
crack the surrounding soil, and help to make the interstices into which
the new rootlets grow?� * * *

�Throughout almost the whole of organic nature the spiral form is more
or less distinctly marked. Now, motion under resistance takes a spiral
direction, as may be seen by the motion of a body rising or falling
through water. A bubble rising rapidly in water describes a spiral
closely resembling a corkscrew, and a body of moderate specific gravity
dropped into water may be seen to fall in a curved direction, the spiral
tendency of which may be distinctly observed. * * * In this prevailing
spiral form of organic bodies, therefore, it appears to me, that there
is presented a strong _prima facie_ case for the view I have maintained.
* * * The spiral form of the branches of many trees is very apparent,
and the universally spiral arrangement of the leaves around the stem of
plants needs only to be referred to. * * * The heart commences as a
spiral turn, and in its perfect form a manifest spiral may be traced
through the left ventricle, right ventricle, right auricle, left auricle
and appendix. And what is the spiral turn in which the heart commences
but a necessary result of the lengthening, under a limit, of the
cellular mass of which it then consists?� * * *

�Every one must have noticed the peculiar curling up of the young leaves
of the common fern. The appearance is as if the leaf were rolled up, but
in truth this form is merely a phenomenon of growth. The curvature
results from the increase of the leaf, it is only another form of the
wrinkling up, or turning at right angles by extension under limit.�

�The rolling up or imbrication of the petals in many flower-buds is a
similar thing; at an early period the small petals may be seen lying
side by side, afterwards growing within the capsule, they become folded
round one another.� * * *

�If a flower-bud be opened at a sufficiently early period, the stamens
will be found as if moulded in the cavity between the pistil and the
corolla, which cavity the antlers exactly fill; the stalks lengthen at
an after period. I have noticed also in a few instances, that in those
flowers in which the petals are imbricated, or twisted together, the
pistil is tapering as growing up between the petals; in some flowers
which have the petals so arranged in the bud as to form a dome (as the
hawthorn; e. g.), the pistil is flattened at the apex, and in the bud
occupies a space precisely limited by the stamens below, and the
enclosing petals above and at the sides. I have not, however, satisfied
myself that this holds good in all cases.�

Without endorsing all Mr. Hinton�s illustrations, to some of which
exception might be taken, his conclusion may be accepted as a large
instalment of the truth. It is, however, to be remarked, that in the
case of organic growth, as in all other cases, the line of movement is
in strictness the resultant of tractive and resistant forces; and that
the tractive forces here form so considerable an element that the
formula is scarcely complete without them. The shapes of plants are
manifestly modified by gravitation: the direction of each branch is not
what it would have been were the tractive force of the Earth absent; and
every flower and leaf is somewhat altered in the course of development
by the weight of its parts. Though in animals such effects are less
conspicuous, yet the instances in which flexible organs have their
directions in great measure determined by gravity, justify the assertion
that throughout the whole organism the forms of parts must be affected
by this force.

The organic movements which constitute growth, are not, however, the
only organic movements to be interpreted. There are also those which
constitute function. And throughout these the same general principles
are discernible. That the vessels along which blood, lymph, bile, and
all the secretions, find their ways, are channels of least resistance,
is a fact almost too conspicuous to be named as an illustration. Less
conspicuous, however, is the truth, that the currents setting along
these vessels are affected by the tractive force of the Earth: witness
varicose veins; witness the relief to an inflamed part obtained by
raising it; witness the congestion of head and face produced by
stooping. And in the fact that dropsy in the legs gets greater by day
and decreases at night, while, conversely, that �dematous fullness under
the eyes common in debility, grows worse during the hours of reclining
and decreases after getting up, shows us how the transudation of fluid
through the walls of the capillaries, varies according as change of
position changes the effect of gravity in different parts of the body.

It may be well in passing just to note the bearing of the principle on
the development of species. From a dynamic point of view, �natural
selection� is the evolution of Life along lines of least resistance. The
multiplication of any kind of plant or animal in localities that are
favourable to it, is a growth where the antagonistic forces are less
than elsewhere. And the preservation of varieties that succeed better
than their allies in coping with surrounding conditions, is the
continuance of vital movement in those directions where the obstacles to
it are most eluded.

                  *       *       *       *       *

§ 90. Throughout the phenomena of mind the law enunciated is not so
readily established. In a large part of them, as those of thought and
emotion, there is no perceptible movement. Even in sensation and
volition, which show us in one part of the body an effect produced by a
force applied to another part, the intermediate movement is inferential
rather than visible. Such indeed are the difficulties that it is not
possible here to do more than briefly indicate the proofs which might be
given did space permit.

Supposing the various forces throughout an organism to be previously in
equilibrium, then any part which becomes the seat of a further force,
added or liberated, must be one from which the force, being resisted by
smaller forces around, will initiate motion towards some other part of
the organism. If elsewhere in the organism there is a point at which
force is being expended, and which so is becoming minus a force which it
before had, instead of plus a force which it before had not, and thus is
made a point at which the re-action against surrounding forces is
diminished; then, manifestly, a motion taking place between the first
and the last of these points is a motion along the line of least
resistance. Now a sensation implies a force added to, or evolved in,
that part of the organism which is its seat; while a mechanical movement
implies an expenditure or loss of force in that part of the organism
which is its seat. Hence if, as we find to be the fact, motion is
habitually propagated from those parts of an organism to which the
external world adds forces in the shape of nervous impressions, to those
parts of an organism which react on the external world through muscular
contractions, it is simply a fulfilment of the law above enunciated.
      From this general conclusion we may pass to a more special one.
When there is anything in the circumstances of an animal�s life,
involving that a sensation in one particular place is habitually
followed by a contraction in another particular place�when there is thus
a frequently-repeated motion through the organism between these places;
what must be the result as respects the line along which the motions
take place? Restoration of equilibrium between the points at which the
forces have been increased and decreased, must take place through some
channel. If this channel is affected by the discharge�if the obstructive
action of the tissues traversed, involves any reaction upon them,
deducting from their obstructive power; then a subsequent motion between
these two points will meet with less resistance along this channel than
the previous motion met with; and will consequently take this channel
still more decidedly. If so, every repetition will still further
diminish the resistance offered by this route; and hence will gradually
be formed between the two a permanent line of communication, differing
greatly from the surrounding tissue in respect of the ease with which
force traverses it. We see, therefore, that if between a particular
impression and a particular motion associated with it, there is
established a connexion producing what is called reflex action, the law
that motion follows the line of least resistance, and that, if the
conditions remain constant, resistance in any direction is diminished by
motion occurring in that direction, supplies an explanation.
      Without further details it will be manifest that a like
interpretation may be given to the succession of all other nervous
changes. If in the surrounding world there are objects, attributes, or
actions, that usually occur together, the effects severally produced by
them in the organism will become so connected by those repetitions which
we call experience, that they also will occur together. In proportion to
the frequency with which any external connexion of phenomena is
experienced, will be the strength of the answering internal connexion of
nervous states. Thus there will arise all degrees of cohesion among
nervous states, as there are all degrees of commonness among the
surrounding co-existences and sequences that generate them: whence must
result a general correspondence between associated ideas and associated
actions in the environment.[13]

The relation between emotions and actions may be similarly construed. As
a first illustration let us observe what happens with emotions that are
undirected by volitions. These, like feelings in general, expend
themselves in generating organic changes, and chiefly in muscular
contractions. As was pointed out in the last chapter, there result
movements of the involuntary and voluntary muscles, that are great in
proportion as the emotions are strong. It remains here to be pointed
out, however, that the order in which these muscles are affected is
explicable only on the principle above set forth. Thus, a pleasurable or
painful state of mind of but slight intensity, does little more than
increase the pulsations of the heart. Why? For the reason that the
relation between nervous excitement and vascular contraction, being
common to every genus and species of feeling, is the one of most
frequent repetition; that hence the nervous connexion is, in the way
above shown, the one which offers the least resistance to a discharge;
and is therefore the one along which a feeble force produces motion. A
sentiment or passion that is somewhat stronger, affects not only the
heart but the muscles of the face, and especially those around the
mouth. Here the like explanation applies; since these muscles, being
both comparatively small, and, for purposes of speech, perpetually used,
offer less resistance than other voluntary muscles to the nerve-motor
force. By a further increase of emotion the respiratory and vocal
muscles become perceptibly excited. Finally, under strong passion, the
muscles in general of the trunk and limbs are violently contracted.
Without saying that the facts can be thus interpreted in all their
details (a task requiring data impossible to obtain) it may be safely
said that the order of excitation is from muscles that are small and
frequently acted on, to those which are larger and less frequently acted
on. The single instance of laughter, which is an undirected discharge of
feeling that affects first the muscles round the mouth, then those of
the vocal and respiratory apparatus, then those of the limbs, and then
those of the spine;[14] suffices to show that when no special route is
opened for it, a force evolved in the nervous centres produces motion
along channels which offer the least resistance, and if it is too great
to escape by these, produces motion along channels offering successively
greater resistance.

Probably it will be thought impossible to extend this reasoning so as to
include volitions. Yet we are not without evidence that the transition
from special desires to special muscular acts, conforms to the same
principle. It may be shown that the mental antecedents of a voluntary
movement, are antecedents which temporarily make the line along which
this movement takes place, the line of least resistance. For a volition,
suggested as it necessarily is by some previous thought connected with
it by associations that determine the transition, is itself a
representation of the movements that are willed, and of their sequences.
But to represent in consciousness certain of our own movements, is
partially to arouse the sensations accompanying such movements,
inclusive of those of muscular tension�is partially to excite the
appropriate motor-nerves and all the other nerves implicated. That is to
say, the volition is itself an incipient discharge along a line which
previous experiences have rendered a line of least resistance. And the
passing of volition into action is simply a completion of the discharge.

One corollary from this must be noted before proceeding; namely, that
the particular set of muscular movements by which any object of desire
is reached, are movements implying the smallest total of forces to be
overcome. As each feeling generates motion along the line of least
resistance, it is tolerably clear that a group of feelings, constituting
a more or less complex desire, will generate motion along a series of
lines of least resistance. That is to say, the desired end will be
achieved with the smallest expenditure of effort. Should it be objected
that through want of knowledge or want of skill, a man often pursues the
more laborious of two courses, and so overcomes a larger total of
opposing forces than was necessary; the reply is, that relatively to his
mental state the course he takes is that which presents the fewest
difficulties. Though there is another which in the abstract is easier,
yet his ignorance of it, or inability to adopt it, is, physically
considered, the existence of an insuperable obstacle to the discharge of
his energies in that direction. Experience obtained by himself, or
communicated by others, has not established in him such channels of
nervous communication as are required to make this better course the
course of least resistance to him.

                  *       *       *       *       *

§ 91. As in individual animals, inclusive of man, motion follows lines
of least resistance, it is to be inferred that among aggregations of
men, the like will hold good. The changes in a society, being due to the
joint actions of its members, the courses of such changes will be
determined as are those of all other changes wrought by composition of
forces.

Thus when we contemplate a society as an organism, and observe the
direction of its growth, we find this direction to be that in which the
average of opposing forces is the least. Its units have energies to be
expended in self-maintenance and reproduction. These energies are met by
various environing energies that are antagonistic to them�those of
geological origin, those of climate, of wild animals, of other human
races with whom they are at enmity or in competition. And the tracts the
society spreads over, are those in which there is the smallest total
antagonism. Or, reducing the matter to its ultimate terms, we may say
that these social units have jointly and severally to preserve
themselves and their offspring from those inorganic and organic forces
which are ever tending to destroy them (either indirectly by oxidation
and by undue abstraction of heat, or directly by bodily mutilation);
that these forces are either counteracted by others which are available
in the shape of food, clothing, habitations, and appliances of defence,
or are, as far as may be, eluded; and that population spreads in
whichever directions there is the readiest escape from these forces, or
the least exertion in obtaining the materials for resisting them, or
both.       For these reasons it happens that fertile valleys where
water and vegetal produce abound, are early peopled. Sea-shores, too,
supplying a large amount of easily-gathered food, are lines along which
mankind have commonly spread. The general fact that, so far as we can
judge from the traces left by them, large societies first appeared in
those tropical regions where the fruits of the earth are obtainable with
comparatively little exertion, and where the cost of maintaining bodily
heat is but slight, is a fact of like meaning. And to these instances
may be added the allied one daily furnished by emigration; which we see
going on towards countries presenting the fewest obstacles to the
self-preservation of individuals, and therefore to national growth.
      Similarly with that resistance to the movements of a society which
neighbouring societies offer. Each of the tribes or nations inhabiting
any region, increases in numbers until it outgrows its means of
subsistence. In each there is thus a force ever pressing outwards on to
adjacent areas�a force antagonized by like forces in the tribes or
nations occupying those areas. And the ever-recurring wars that
result�the conquests of weaker tribes or nations, and the over-running
of their territories by the victors, are instances of social movements
taking place in the directions of least resistance. Nor do the conquered
peoples, when they escape extermination or enslavement, fail to show us
movements that are similarly determined. For migrating as they do to
less fertile regions�taking refuge in deserts or among mountains�moving
in a direction where the resistance to social growth is comparatively
great; they still do this only under an excess of pressure in all other
directions: the physical obstacles to self-preservation they encounter,
being really less than the obstacles offered by the enemies from whom
they fly.

Internal social movements may also be thus interpreted. Localities
naturally fitted for producing particular commodities�that is,
localities in which such commodities are got at the least cost of
force�that is, localities in which the desires for these commodities
meet with the least resistance; become localities especially devoted to
the obtainment of these commodities. Where soil and climate render wheat
a profitable crop, or a crop from which the greatest amount of
life-sustaining power is gained by a given quantity of effort, the
growth of wheat becomes the dominant industry. Where wheat cannot be
economically produced, oats, or rye, or maize, or rice, or potatoes, is
the agricultural staple. Along sea-shores men support themselves with
least effort by catching fish; and hence choose fishing as an
occupation. And in places that are rich in coal or metallic ores, the
population, finding that labour devoted to the raising of these
materials brings a larger return of food and clothing than when
otherwise directed, becomes a population of miners.       This last
instance introduces us to the phenomena of exchange; which equally
illustrate the general law. For the practice of barter begins as soon as
it facilitates the fulfilment of men�s desires, by diminishing the
exertion needed to reach the objects of those desires. When instead of
growing his own corn, weaving his own cloth, sewing his own shoes, each
man began to confine himself to farming, or weaving, or shoemaking; it
was because each found it more laborious to make everything he wanted,
than to make a great quantity of one thing and barter the surplus for
the rest: by exchange, each procured the necessaries of life without
encountering so much resistance. Moreover, in deciding what commodity to
produce, each citizen was, as he is at the present day, guided in the
same manner. For besides those local conditions which determine whole
sections of a society towards the industries easiest for them, there are
also individual conditions and individual aptitudes which to each
citizen render certain occupations preferable; and in choosing those
forms of activity which their special circumstances and faculties
dictate, these social units are severally moving towards the objects of
their desires in the directions which present to them the fewest
obstacles.       The process of transfer which commerce pre-supposes,
supplies another series of examples. So long as the forces to be
overcome in procuring any necessary of life in the district where it is
consumed, are less than the forces to be overcome in procuring it from
an adjacent district, exchange does not take place. But when the
adjacent district produces it with an economy that is not out-balanced
by cost of transit�when the distance is so small and the route so easy
that the labour of conveyance plus the labour of production is less than
the labour of production in the consuming district, transfer commences.
Movement in the direction of least resistance is also seen in the
establishment of the channels along which intercourse takes place. At
the outset, when goods are carried on the backs of men and horses, the
paths chosen are those which combine shortness with levelness and
freedom from obstacles�those which are achieved with the smallest
exertion. And in the subsequent formation of each highway, the course
taken is that which deviates horizontally from a straight line so far
only as is needful to avoid vertical deviations entailing greater labour
in draught. The smallest total of obstructive forces determines the
route, even in seemingly exceptional cases; as where a detour is made to
avoid the opposition of a landowner. All subsequent improvements, ending
in macadamized roads, canals, and railways, which reduce the antagonism
of friction and gravity to a minimum, exemplify the same truth. After
there comes to be a choice of roads between one point and another, we
still see that the road chosen is that along which the cost of transit
is the least: cost being the measure of resistance. Even where, time
being a consideration, the more expensive route is followed, it is so
because the loss of time involves loss of force.       When, division of
labour having been carried to a considerable extent and means of
communication made easy, there arises a marked localization of
industries, the relative growths of the populations devoted to them may
be interpreted on the same principle. The influx of people to each
industrial centre, as well as the rate of multiplication of those
already inhabiting it, is determined by the payment for labour; that
is�by the quantity of commodities which a given amount of effort will
obtain. To say that artisans flock to places where, in consequence of
facilities for production, an extra proportion of produce can be given
in the shape of wages; is to say that they flock to places where there
are the smallest obstacles to the support of themselves and families.
Hence, the rapid increase of number which occurs in such places, is
really a social growth at points where the opposing forces are the
least.

Nor is the law less clearly to be traced in those functional changes
daily going on. The flow of capital into businesses yielding the largest
returns; the buying in the cheapest market and selling in the dearest;
the introduction of more economical modes of manufacture; the
development of better agencies for distribution; and all those
variations in the currents of trade that are noted in our newspapers and
telegrams from hour to hour; exhibit movement taking place in directions
where it is met by the smallest total of opposing forces. For if we
analyze each of these changes�if instead of interest on capital we read
surplus of products which remains after maintenance of labourers; if we
so interpret large interest or large surplus to imply labour expended
with the greatest results; and if labour expended with the greatest
results means muscular action so directed as to evade obstacles as far
as possible; we see that all these commercial phenomena are complicated
motions set up along lines of least resistance.

Objections of two opposite kinds will perhaps be made to these
sociological applications of the law. By some it may be said that the
term force as here used, is used metaphorically�that to speak of men as
_impelled_ in certain directions by certain desires, is a figure of
speech and not the statement of a physical fact. The reply is, that the
foregoing illustrations are to be interpreted literally, and that the
processes described _are_ physical ones. The pressure of hunger is an
actual force�a sensation implying some state of nervous tension; and the
muscular action which the sensation prompts is really a discharge of it
in the shape of bodily motion�a discharge which, on analyzing the mental
acts involved, will be found to follow lines of least resistance. Hence
the motions of a society whose members are impelled by this or any other
desire, are actually, and not metaphorically, to be understood in the
manner shown.       An opposite objection may possibly be, that the
several illustrations given are elaborated truisms; and that the law of
direction of motion being once recognized, the fact that social
movements, in common with all others, must conform to it, follows
inevitably. To this it may be rejoined, that a mere abstract assertion
that social movements must do this, would carry no conviction to the
majority; and that it is needful to show _how_ they do it. For social
evolution to be interpreted after the method proposed, it is requisite
that such generalisations as those of political economy shall be reduced
to equivalent propositions expressed in terms of force and motion.

Social movements of these various orders severally conform to the two
derivative principles named at the outset. In the first place we may
observe how, once set up in given directions, such movements, like all
others, tend to continue in these directions. A commercial mania or
panic, a current of commodities, a social custom, a political agitation,
or a popular delusion, maintains its course for a long time after its
original source has ceased; and requires antagonistic forces to arrest
it. In the second place it is to be noted that in proportion to the
complexity of social forces is the tortuousness of social movements. The
involved series of muscular contractions gone through by the artizan,
that he may get the wherewithal to buy a loaf lying at the baker�s next
door, show us how extreme becomes the indirectness of motion when the
agencies at work become very numerous�a truth still better illustrated
by the more public social actions; as those which end in bringing a
successful man of business, towards the close of his life, into
parliament.

                  *       *       *       *       *

§ 92. And now of the general truth set forth in this chapter, as of that
dealt with in the last, let us ask�what is our ultimate evidence? Must
we accept it simply as an empirical generalization? or is it to be
established as a corollary from a still deeper truth? The reader will
anticipate the answer. We shall find it deducible from that datum of
consciousness which underlies all science.

Suppose several tractive forces, variously directed, to be acting on a
given body. By what is known among mathematicians as the composition of
forces, there may be found for any two of these, a single force of such
amount and direction as to produce on the body an exactly equal effect.
If in the direction of each of them there be drawn a straight line, and
if the lengths of these two straight lines be made proportionate to the
amounts of the forces; and if from the end of each line there be drawn a
line parallel to the other, so as to complete a parallelogram; then the
diagonal of this parallelogram represents the amount and direction of a
force that is equivalent to the two. Such a resultant force, as it is
called, may be found for any pair of forces throughout the group.
Similarly, for any pair of such resultants a single resultant may be
found. And by repeating this course, all of them may be reduced to two.
If these two are equal and opposite�that is, if there is no line of
greatest traction, motion does not take place. If they are opposite but
not equal, motion takes place in the direction of the greater. And if
they are neither equal nor opposite, motion takes place in the direction
of their resultant. For in either of these cases there is an
unantagonized force in one direction. And this residuary force that is
not neutralized by an opposing one, must move the body in the direction
in which it is acting. To assert the contrary is to assert that a force
can be expended without effect�without generating an equivalent force;
and by so implying that force can cease to exist, this involves a denial
of the persistence of force.       It needs scarcely be added that if in
place of tractions we take resistances, the argument equally holds; and
that it holds also where both tractions and resistances are concerned.
Thus the law that motion follows the line of greatest traction, or the
line of least resistance, or the resultant of the two, is a necessary
deduction from that primordial truth which transcends proof.

Reduce the proposition to its simplest form, and it becomes still more
obviously consequent on the persistence of force. Suppose two weights
suspended over a pulley or from the ends of an equal-armed lever; or
better still�suppose two men pulling against each other. In such cases
we say that the heavier weight will descend, and that the stronger man
will draw the weaker towards him. But now, if we are asked how we know
which is the heavier weight or the stronger man; we can only reply that
it is the one producing motion in the direction of its pull. Our only
evidence of excess of force is the movement it produces. But if of two
opposing tractions we can know one as greater than the other only by the
motion it generates in its own direction, then the assertion that motion
occurs in the direction of greatest traction is a truism. When, going a
step further back, we seek a warrant for the assumption that of the two
conflicting forces, that is the greater which produces motion in its own
direction, we find no other than the consciousness that such part of the
greater force as is unneutralized by the lesser, must produce its
effect�the consciousness that this residuary force cannot disappear, but
must manifest itself in some equivalent change�the consciousness that
force is persistent.       Here too, as before, it may be remarked that
no amount of varied illustrations, like those of which this chapter
mainly consists, can give greater certainty to the conclusion thus
immediately drawn from the ultimate datum of consciousness. For in all
cases, as in the simple ones just given, we can identify the greatest
force only by the resulting motion. It is impossible for us ever to get
evidence of the occurrence of motion in any other direction than that of
the greatest force; since our measure of relative greatness among forces
is their relative power of generating motion. And clearly, while the
comparative greatness of forces is thus determined, no multiplication of
instances can add certainty to a law of direction of movement which
follows immediately from the persistence of force.

From this same primordial truth, too, may be deduced the principle that
motion once set up along any line, becomes itself a cause of subsequent
motion along that line. The mechanical axiom that, if left to itself,
matter moving in any direction will continue in that direction with
undiminished velocity, is but an indirect assertion of the persistence
of force; since it is an assertion that the force manifested in the
transfer of a body along a certain length of a certain line in a certain
time, cannot disappear without producing some equal manifestation�a
manifestation which, in the absence of conflicting forces, must be a
further transfer in the same direction at the same velocity.       In
the case of matter traversing matter the like inference is necessitated.
Here indeed the actions are much more complicated. A liquid that follows
a certain channel through or over a solid, as water along the Earth�s
surface, loses part of its motion in the shape of heat, through friction
and collision with the matters forming its bed. A further amount of its
motion may be absorbed in overcoming forces which it liberates; as when
it loosens a mass which falls into, and blocks up, its channel. But
after these deductions by transformation into other modes of force, any
further deduction from the motion of the water is at the expense of a
reaction on the channel, which by so much diminishes its obstructive
power: such reaction being shown in the motion acquired by the detached
portions which are carried away. The cutting out of river-courses is a
perpetual illustration of this truth.       Still more involved is the
case of motion passing through matter by impulse from part to part; as a
nervous discharge through animal tissue. Some chemical change may be
wrought along the route traversed, which may render it less fit than
before for conveying a current. Or the motion may itself be in part
metamorphosed into some obstructive form of force; as in metals, the
conducting power of which is, for the time, decreased by the heat which
the passage of electricity itself generates. The real question is,
however, what structural modification, if any, is produced throughout
the matter traversed, apart from _incidental_ disturbing forces�apart
from everything but the _necessary_ resistance of the matter: that,
namely, which results from the inertia of its units. If we confine our
attention to that part of the motion which, escaping transformation,
continues its course, then it is a corollary from the persistence of
force that as much of this remaining motion as is taken up in changing
the positions of the units, must leave these by so much less able to
obstruct subsequent motion in the same direction.

Thus in all the changes heretofore and at present displayed by the Solar
System; in all those that have gone on and are still going on in the
Earth�s crust; in all processes of organic development and function; in
all mental actions and the effects they work on the body; and in all
modifications of structure and activity in societies; the implied
movements are of necessity determined in the manner above set forth.
Every alteration in the arrangement of parts, constituting Evolution
under each of its phases, must conform to this universal principle.
Wherever we see motion, its direction must be that of the greatest
force. And wherever we see the greatest force to be acting in a given
direction, in that direction motion must ensue.

-----

Footnote 13:

  This paragraph is a re-statement, somewhat amplified, of an idea set
  forth in the _Medico-Chirurgical Review_ for January, 1859 (pp. 189
  and 190); and contains the germ of the intended fifth part of the
  _Principles of Psychology_, which was withheld for the reasons given
  in the preface to that work.

Footnote 14:

  For details see a paper on �The Physiology of Laughter,� published in
  _Macmillan�s Magazine_ for March 1860.




                              CHAPTER XI.
                         THE RHYTHM OF MOTION.


§ 93. When the pennant of a vessel lying becalmed first shows the coming
breeze, it does so by gentle undulations that travel from its fixed to
its free end. Presently the sails begin to flap; and their blows against
the mast increase in rapidity as the breeze rises. Even when, being
fully bellied out, they are in great part steadied by the strain of the
yards and cordage, their free edges tremble with each stronger gust. And
should there come a gale, the jar that is felt on laying hold of the
shrouds shows that the rigging vibrates; while the rush and whistle of
the wind prove that in it, also, rapid undulations are generated. Ashore
the conflict between the current of air and the things it meets results
in a like rhythmical action. The leaves all shiver in the blast; each
branch oscillates; and every exposed tree sways to and fro. The blades
of grass and dried bents in the meadows, and still better the stalks in
the neighbouring corn-fields, exhibit the same rising and falling
movement. Nor do the more stable objects fail to do the like, though in
a less manifest fashion; as witness the shudder that may be felt
throughout a house during the paroxysms of a violent storm.
      Streams of water produce in opposing objects the same general
effects as do streams of air. Submerged weeds growing in the middle of a
brook, undulate from end to end. Branches brought down by the last
flood, and left entangled at the bottom where the current is rapid, are
thrown into a state of up and down movement that is slow or quick in
proportion as they are large or small; and where, as in great rivers
like the Mississippi, whole trees are thus held, the name �sawyers,� by
which they are locally known, sufficiently describes the rhythm produced
in them. Note again the effect of the antagonism between the current and
its channel. In shallow places, where the action of the bottom on the
water flowing over it is visible, we see a ripple produced�a series of
undulations. And if we study the action and re-action going on between
the moving fluid and its banks, we still find the principle illustrated,
though in a different way. For in every rivulet, as in the mapped-out
course of every great river, the bends of the stream from side to side
throughout its tortuous course constitute a lateral undulation�an
undulation so inevitable that even an artificially straightened channel
is eventually changed into a serpentine one. Analogous phenomena may be
observed where the water is stationary and the solid matter moving. A
stick drawn laterally through the water with much force, proves by the
throb which it communicates to the hand that it is in a state of
vibration. Even where the moving body is massive, it only requires that
great force should be applied to get a sensible effect of like kind:
instance the screw of a screw-steamer, which instead of a smooth
rotation falls into a rapid rhythm that sends a tremor through the whole
vessel.       The sound which results when a bow is drawn over a
violin-string, shows us vibrations produced by the movement of a solid
over a solid. In lathes and planing machines, the attempt to take off a
thick shaving causes a violent jar of the whole apparatus, and the
production of a series of waves on the iron or wood that is cut. Every
boy in scraping his slate-pencil finds it scarcely possible to help
making a ridged surface. If you roll a ball along the ground or over the
ice, there is always more or less up and down movement�a movement that
is visible while the velocity is considerable, but becomes too small and
rapid to be seen by the unaided eye as the velocity diminishes. However
smooth the rails, and however perfectly built the carriages, a
railway-train inevitably gets into oscillations, both lateral and
vertical. Even where moving matter is suddenly arrested by collision,
the law is still illustrated; for both the body striking and the body
struck are made to tremble; and trembling is rhythmical movement. Little
as we habitually observe it, it is yet certain that the impulses our
actions impress from moment to moment on surrounding objects, are
propagated through them in vibrations. It needs but to look through a
telescope of high power, to be convinced that each pulsation of the
heart gives a jar to the whole room.       If we pass to motions of
another order�those namely which take place in the etherial medium�we
still find the same thing. Every fresh discovery confirms the hypothesis
that light consists of undulations. The rays of heat, too, are now found
to have a like fundamental nature; their undulations differing from
those of light only in their comparative length. Nor do the movements of
electricity fail to furnish us with an illustration; though one of a
different order. The northern aurora may often be observed to pulsate
with waves of greater brightness; and the electric discharge through a
vacuum shows us by its stratified appearance that the current is not
uniform, but comes in gushes of greater and lesser intensity.
      Should it be said that at any rate there are some motions, as
those of projectiles, which are not rhythmical, the reply is, that the
exception is apparent only; and that these motions would be rhythmical
if they were not interrupted. It is common to assert that the trajectory
of a cannon ball is a parabola; and it is true that (omitting
atmospheric resistance) the curve described differs so slightly from a
parabola that it may practically be regarded as one. But, strictly
speaking, it is a portion of an extremely eccentric ellipse, having the
Earth�s centre of gravity for its remoter focus; and but for its arrest
by the substance of the Earth, the cannon ball would travel round that
focus and return to the point whence it started; again to repeat this
slow rhythm. Indeed, while seeming at first sight to do the reverse, the
discharge of a cannon furnishes one of the best illustrations of the
principle enunciated. The explosion produces violent undulations in the
surrounding air. The whizz of the shot, as it flies towards its mark, is
due to another series of atmospheric undulations. And the movement to
and from the Earth�s centre, which the cannon ball is beginning to
perform, being checked by solid matter, is transformed into a rhythm of
another order; namely, the vibration which the blow sends through
neighbouring bodies.[15]

Rhythm is very generally not simple but compound. There are usually at
work various forces, causing undulations differing in rapidity; and
hence it continually happens that besides the primary rhythms there are
secondary rhythms, produced by the periodic coincidence and antagonism
of the primary ones. Double, triple, and even quadruple rhythms, are
thus generated. One of the simplest instances is afforded by what in
acoustics are known as �beats:� recurring intervals of sound and silence
which are perceived when two notes of nearly the same pitch are struck
together; and which are due to the alternate correspondence and
antagonism of the atmospheric waves. In like manner the various
phenomena due to what is called interference of light, severally result
from the periodic agreement and disagreement of etherial
undulations�undulations which, by alternately intensifying and
neutralizing each other, produce intervals of increased and diminished
light. On the sea-shore may be noted sundry instances of compound
rhythm. We have that of the tides, in which the daily rise and fall
undergoes a fortnightly increase and decrease, due to the alternate
coincidence and antagonism of the solar and lunar attractions. We have
again that which is perpetually furnished by the surface of the sea:
every large wave bearing smaller ones on its sides, and these still
smaller ones; with the result that each flake of foam, along with the
portion of water bearing it, undergoes minor ascents and descents of
several orders while it is being raised and lowered by the greater
billows. A quite different and very interesting example of compound
rhythm, occurs in the little rills which, at low tide, run over the sand
out of the shingle banks above. Where the channel of one of these is
narrow, and the stream runs strongly, the sand at the bottom is raised
into a series of ridges corresponding to the ripple of the water. On
watching for a short time, it will be seen that these ridges are being
raised higher and the ripple growing stronger; until at length, the
action becoming violent, the whole series of ridges is suddenly swept
away, the stream runs smoothly, and the process commences afresh.
Instances of still more complex rhythms might be added; but they will
come more appropriately in connexion with the several forms of
Evolution, hereafter to be dealt with.

From the ensemble of the facts as above set forth, it will be seen that
rhythm results wherever there is a conflict of forces not in
equilibrium. If the antagonist forces at any point are balanced, there
is rest; and in the absence of motion there can of course be no rhythm.
But if instead of a balance there is an excess of force in one
direction�if, as necessarily follows, motion is set up in that
direction; then for that motion to continue uniformly in that direction,
it is requisite that the moving matter should, notwithstanding its
unceasing change of place, present unchanging relations to the sources
of force by which its motion is produced and opposed. This however is
impossible. Every further transfer through space must alter the ratio
between the forces concerned�must increase or decrease the predominance
of one force over the other�must prevent uniformity of movement. And if
the movement cannot be uniform, then, in the absence of acceleration or
retardation continued through infinite time and space, (results which
cannot be conceived) the only alternative is rhythm.

A secondary conclusion must not be omitted. In the last chapter we saw
that motion is never absolutely rectilinear; and here it remains to be
added that, as a consequence, rhythm is necessarily incomplete. A truly
rectilinear rhythm can arise only when the opposing forces are in
exactly the same line; and the probabilities against this are infinitely
great. To generate a perfectly circular rhythm, the two forces concerned
must be exactly at right angles to each other, and must have exactly a
certain ratio; and against this the probabilities are likewise
infinitely great. All other proportions and directions of the two forces
will produce an ellipse of greater or less eccentricity. And when, as
indeed always happens, above two forces are engaged, the curve described
must be more complex; and cannot exactly repeat itself. So that in fact
throughout nature, this action and re-action of forces never brings
about a complete return to a previous state. Where the movement is very
involved, and especially where it is that of some aggregate whose units
are partially independent, anything like a regular curve is no longer
traceable; we see nothing more than a general oscillation. And on the
completion of any periodic movement, the degree in which the state
arrived at differs from the state departed from, is usually marked in
proportion as the influences at work are numerous.

                  *       *       *       *       *

§ 94. That spiral arrangement so general among the more diffused
nebulæ�an arrangement which must be assumed by matter moving towards a
centre of gravity through a resisting medium�shows us the progressive
establishment of revolution, and therefore of rhythm; in those remote
spaces which the nebulæ occupy. Double stars, moving round common
centres of gravity in periods some of which are now ascertained, exhibit
settled rhythmical actions in distant parts of our sidereal system. And
another fact which, though of a different order, has a like general
significance, is furnished by variable stars�stars which alternately
brighten and fade.

The periodicities of the planets, satellites, and comets, are so
familiar that it would be inexcusable to name them, were it not needful
here to point out that they are so many grand illustrations of this
general law of movement. But besides the revolutions of these bodies in
their orbits (all more or less excentric) and their rotations on their
axes, the Solar System presents us with various rhythms of a less
manifest and more complex kind. In each planet and satellite there is
the revolution of the nodes�a slow change in the position of the
orbit-plane, which after completing itself commences afresh. There is
the gradual alteration in the length of the axis major of the orbit; and
also of its excentricity: both of which are rhythmical alike in the
sense that they alternate between maxima and minima, and in the sense
that the progress from one extreme to the other is not uniform, but is
made with fluctuating velocity. Then, too, there is the revolution of
the line of apsides, which in course of time moves round the heavens�not
regularly, but through complex oscillations. And further we have
variations in the directions of the planetary axes�that known as
nutation, and that larger gyration which, in the case of the Earth,
causes the precession of the equinoxes.       These rhythms, already
more or less compound, are compounded with each other. Such an instance
as the secular acceleration and retardation of the moon, consequent on
the varying excentricity of the Earth�s orbit, is one of the simplest.
Another, having more important consequences, results from the changing
direction of the axes of rotation in planets whose orbits are decidedly
excentric. Every planet, during a certain long period, presents more of
its northern than of its southern hemisphere to the sun at the time of
its nearest approach to him; and then again, during a like period,
presents more of its southern hemisphere than of its northern�a
recurring coincidence which, though causing in some planets no sensible
alterations of climate, involves in the case of the Earth an epoch of
21,000 years, during which each hemisphere goes through a cycle of
temperate seasons, and seasons that are extreme in their heat and cold.
Nor is this all. There is even a variation of this variation. For the
summers and winters of the whole Earth become more or less strongly
contrasted, as the excentricity of its orbit increases and decreases.
Hence during increase of the excentricity, the epochs of moderately
contrasted seasons and epochs of strongly contrasted seasons, through
which alternately each hemisphere passes, must grow more and more
different in the degrees of their contrasts; and contrariwise during
decrease of the excentricity. So that in the quantity of light and heat
which any portion of the Earth receives from the sun, there goes on a
quadruple rhythm: that of day and night; that of summer and winter; that
due to the changing position of the axis at perihelion and aphelion,
taking 21,000 years to complete; and that involved by the variation of
the orbit�s excentricity, gone through in millions of years.

                  *       *       *       *       *

§ 95. Those terrestrial processes whose dependence on the solar heat is
direct, of course exhibit a rhythm that corresponds to the periodically
changing amount of heat which each part of the Earth receives. The
simplest, though the least obtrusive, instance is supplied by the
magnetic variations. In these there is a diurnal increase and decrease,
an annual increase and decrease, and a decennial increase and decrease;
the latter answering to a period during which the solar spots become
alternately abundant and scarce: besides which known variations there
are probably others corresponding with the astronomical cycles just
described. More obvious examples are furnished by the movements of the
ocean and the atmosphere. Marine currents from the equator to the poles
above, and from the poles to the equator beneath, show us an unceasing
backward and forward motion throughout this vast mass of water�a motion
varying in amount according to the seasons, and compounded with smaller
like motions of local origin. The similarly-caused general currents in
the air, have similar annual variations similarly modified. Irregular as
they are in detail, we still see in the monsoons and other tropical
atmospheric disturbances, or even in our own equinoctial gales and
spring east winds, a periodicity sufficiently decided.       Again, we
have an alternation of times during which evaporation predominates with
times during which condensation predominates: shown in the tropics by
strongly marked rainy seasons and seasons of drought, and in the
temperate zones by corresponding changes of which the periodicity,
though less definite, is still traceable. The diffusion and
precipitation of water, besides the slow alternations answering to
different parts of the year, furnish us with examples of rhythm of a
more rapid kind. During wet weather, lasting, let us say, over some
weeks, the tendency to condense, though greater than the tendency to
evaporate, does not show itself in continuous rain; but the period is
made up of rainy days and days that are wholly or partially fair. Nor is
it in this rude alternation only that the law is manifested. During any
day throughout this wet weather a minor rhythm is traceable; and
especially so when the tendencies to evaporate and to condense are
nearly balanced. Among mountains this minor rhythm and its causes may be
studied to great advantage. Moist winds, which do not precipitate their
contained water in passing over the comparatively warm lowlands, lose so
much heat when they reach the cold mountain peaks, that condensation
rapidly takes place. Water, however, in passing from the gaseous to the
fluid state, gives out a considerable amount of heat; and hence the
resulting clouds are warmer than the air that precipitates them, and
much warmer than the high rocky surfaces round which they fold
themselves. Hence in the course of the storm, these high rocky surfaces
are raised in temperature, partly by radiation from the enwrapping
cloud, partly by contact of the falling rain-drops. Giving off more heat
than before, they no longer lower so greatly the temperature of the air
passing over them; and so cease to precipitate its contained water. The
clouds break; the sky begins to clear; and a gleam of sunshine promises
that the day is going to be fine. But the small supply of heat which the
cold mountain�s sides have received, is soon lost: especially when the
dispersion of the clouds permits free radiation into space. Very soon,
therefore, these elevated surfaces, becoming as cold as at first, (or
perhaps even colder in virtue of the evaporation set up,) begin again to
condense the vapour in the air above; and there comes another storm,
followed by the same effects as before. In lowland regions this action
and reaction is usually less conspicuous, because the contrast of
temperatures is less marked. Even here, however, it may be traced; and
that not only on showery days, but on days of continuous rain; for in
these we do not see uniformity: always there are fits of harder and
gentler rain that are probably caused as above explained.

Of course these meteorologic rhythms involve something corresponding to
them in the changes wrought by wind and water on the Earth�s surface.
Variations in the quantities of sediment brought down by rivers that
rise and fall with the seasons, must cause variations in the resulting
strata�alternations of colour or quality in the successive laminæ. Beds
formed from the detritus of shores worn down and carried away by the
waves, must similarly show periodic differences answering to the
periodic winds of the locality. In so far as frost influences the rate
of denudation, its recurrence is a factor in the rhythm of sedimentary
deposits. And the geological changes produced by glaciers and icebergs
must similarly have their alternating periods of greater and less
intensity.

There is evidence also that modifications in the Earth�s crust due to
igneous action have a certain periodicity. Volcanic eruptions are not
continuous but intermittent, and as far as the data enable us to judge,
have a certain average rate of recurrence; which rate of recurrence is
complicated by rising into epochs of greater activity and falling into
epochs of comparative quiescence. So too is it with earthquakes and the
elevations or depressions caused by them. At the mouth of the
Mississippi, the alternation of strata gives decisive proof of
successive sinkings of the surface, that have taken place at tolerably
equal intervals. Everywhere, in the extensive groups of conformable
strata that imply small subsidences recurring with a certain average
frequency, we see a rhythm in the action and reaction between the
Earth�s crust and its molten contents�a rhythm compounded with those
slower ones shown in the termination of groups of strata, and the
commencement of other groups not conformable to them.       There is
even reason for suspecting a geological periodicity that is immensely
slower and far wider in its effects; namely, an alternation of those
vast upheavals and submergencies by which continents are produced where
there were oceans, and oceans where there were continents. For
supposing, as we may fairly do, that the Earth�s crust is throughout of
tolerably equal thickness, it is manifest that such portions of it as
become most depressed below the average level, must have their inner
surfaces most exposed to the currents of molten matter circulating
within, and will therefore undergo a larger amount of what may be called
igneous denudation; while, conversely, the withdrawal of the inner
surfaces from these currents where the Earth�s crust is most elevated,
will cause a thickening more or less compensating the aqueous denudation
going on externally. Hence those depressed areas over which the deepest
oceans lie, being gradually thinned beneath and not covered by much
sedimentary deposit above, will become areas of least resistance, and
will then begin to yield to the upward pressure of the Earth�s contents;
whence will result, throughout such areas, long-continued elevations,
ceasing only when the reverse state of things has been brought about.
Whether this speculation be well or ill founded, does not however affect
the general conclusion. Apart from it we have sufficient evidence that
geologic processes are rhythmical.

                  *       *       *       *       *

§ 96. Perhaps nowhere are the illustrations of rhythm so numerous and so
manifest as among the phenomena of life. Plants do not, indeed, usually
show us any decided periodicities, save those determined by day and
night and by the seasons. But in animals we have a great variety of
movements in which the alternation of opposite extremes goes on with all
degrees of rapidity. The swallowing of food is effected by a wave of
constriction passing along the �sophagus; its digestion is accompanied
by a muscular action of the stomach that is also undulatory; and the
peristaltic motion of the intestines is of like nature. The blood
obtained from this food is propelled not in a uniform current but in
pulses; and it is aerated by lungs that alternately contract and expand.
All locomotion results from oscillating movements: even where it is
apparently continuous, as in many minute forms, the microscope proves
the vibration of cilia to be the agency by which the creature is moved
smoothly forwards.

Primary rhythms of the organic actions are compounded with secondary
ones of longer duration. These various modes of activity have their
recurring periods of increase and decrease. We see this in the periodic
need for food, and in the periodic need for repose. Each meal induces a
more rapid rhythmic action of the digestive organs; the pulsation of the
heart is accelerated; and the inspirations become more frequent. During
sleep, on the contrary, these several movements slacken. So that in the
course of the twenty-four hours, those small undulations of which the
different kinds of organic action are constituted, undergo one long wave
of increase and decrease, complicated with several minor waves.
      Experiments have shown that there are still slower rises and falls
of functional activity. Waste and assimilation are not balanced by every
meal, but one or other maintains for some time a slight excess; so that
a person in ordinary health is found to undergo an increase and decrease
of weight during recurring intervals of tolerable equality. Besides
these regular periods there are still longer and comparatively irregular
ones; namely, those alternations of greater and less vigour, which even
healthy people experience. So inevitable are these oscillations that
even men in training cannot be kept stationary at their highest power,
but when they have reached it begin to retrograde.       Further
evidence of rhythm in the vital movements is furnished by invalids.
Sundry disorders are named from the intermittent character of their
symptoms. Even where the periodicity is not very marked, it is mostly
traceable. Patients rarely if ever get uniformly worse; and
convalescents have usually their days of partial relapse or of less
decided advance.

Aggregates of living creatures illustrate the general truth in other
ways. If each species of organism be regarded as a whole, it displays
two kinds of rhythm. Life as it exists in all the members of such
species, is an extremely complex kind of movement, more or less distinct
from the kinds of movement which constitutes life in other species. In
each individual of the species, this extremely complex kind of movement
begins, rises to its climax, declines, and ceases in death. And every
successive generation thus exhibits a wave of that peculiar activity
characterizing the species as a whole.       The other form of rhythm is
to be traced in that variation of number which each tribe of animals and
plants is ever undergoing. Throughout the unceasing conflict between the
tendency of a species to increase and the antagonistic tendencies, there
is never an equilibrium: one always predominates. In the case even of a
cultivated plant or domesticated animal, where artificial means are used
to maintain the supply at a uniform level, we still see that
oscillations of abundance and scarcity cannot be avoided. And among the
creatures uncared for by man, such oscillations are usually more marked.
After a race of organisms has been greatly thinned by enemies or lack of
food, its surviving members become more favourably circumstanced than
usual. During the decline in their numbers their food has grown
relatively more abundant; while their enemies have diminished from want
of prey. The conditions thus remain for some time favourable to their
increase; and they multiply rapidly. By and by their food is rendered
relatively scarce, at the same time that their enemies have become more
numerous; and the destroying influences being thus in excess, their
number begins to diminish again.       Yet one more rhythm, extremely
slow in its action, may be traced in the phenomena of Life, contemplated
under their most general aspect. The researches of palæontologists show,
that there have been going on, during the vast period of which our
sedimentary rocks bear record, successive changes of organic forms.
Species have appeared, become abundant, and then disappeared. Genera, at
first constituted of but few species, have for a time gone on growing
more multiform; and then have begun to decline in the number of their
subdivisions; leaving at last but one or two representatives, or none at
all. During longer epochs whole orders have thus arisen, culminated, and
dwindled away. And even those wider divisions containing many orders
have similarly undergone a gradual rise, a high tide, and a
long-continued ebb. The stalked _Crinoidea_, for example, which, during
the carboniferous epoch, became abundant, have almost disappeared: only
a single species being extant. Once a large family of molluscs, the
_Brachiopoda_ have now become rare. The shelled Cephalopods, at one time
dominant among the inhabitants of the ocean, both in number of forms and
of individuals, are in our day nearly extinct. And after an �age of
reptiles,� there has come an age in which reptiles have been in great
measure supplanted by mammals. Whether these vast rises and falls of
different kinds of life ever undergo anything approaching to
repetitions, (which they may possibly do in correspondence with those
vast cycles of elevation and subsidence that produce continents and
oceans,) it is sufficiently clear that Life on the Earth has not
progressed uniformly, but in immense undulations.

                  *       *       *       *       *

§ 97. It is not manifest that the changes of consciousness are in any
sense rhythmical. Yet here, too, analysis proves both that the mental
state existing at any moment is not uniform, but is decomposable into
rapid oscillations; and also that mental states pass through longer
intervals of increasing and decreasing intensity.

Though while attending to any single sensation, or any group of related
sensations constituting the consciousness of an object, we seem to
remain for the time in a persistent and homogeneous condition of mind, a
careful self-examination shows that this apparently unbroken mental
state is in truth traversed by a number of minor states, in which
various other sensations and perceptions are rapidly presented and
disappear. From the admitted fact that thinking consists in the
establishment of relations, it is a necessary corollary that the
maintenance of consciousness in any one state to the entire exclusion of
other states, would be a cessation of thought, that is, of
consciousness. So that any seemingly continuous feeling, say of
pressure, really consists of portions of that feeling perpetually
recurring after the momentary intrusion of other feelings and
ideas�quick thoughts concerning the place where it is felt, the external
object producing it, its consequences, and other things suggested by
association. Thus there is going on an extremely rapid departure from,
and return to, that particular mental state which we regard as
persistent. Besides the evidence of rhythm in consciousness which direct
analysis thus affords, we may gather further evidence from the
correlation between feeling and movement. Sensations and emotions expend
themselves in producing muscular contractions. If a sensation or emotion
were strictly continuous, there would be a continuous discharge along
those motor nerves acted upon. But so far as experiments with artificial
stimuli enable us to judge, a continuous discharge along the nerve
leading to a muscle, does not contract it: a broken discharge is
required�a rapid succession of shocks. Hence muscular contraction
pre-supposes that rhythmic state of consciousness which direct
observation discloses.       A much more conspicuous rhythm, having
longer waves, is seen during the outflow of emotion into dancing,
poetry, and music. The current of mental energy that shows itself in
these modes of bodily action, is not continuous, but falls into a
succession of pulses. The measure of a dance is produced by the
alternation of strong muscular contractions with weaker ones; and, save
in measures of the simplest order such as are found among barbarians and
children, this alternation is compounded with longer rises and falls in
the degree of muscular excitement. Poetry is a form of speech which
results when the emphasis is regularly recurrent; that is, when the
muscular effort of pronunciation has definite periods of greater and
less intensity�periods that are complicated with others of like nature
answering to the successive verses. Music, in still more various ways,
exemplifies the law. There are the recurring bars, in each of which
there is a primary and a secondary beat. There is the alternate increase
and decrease of muscular strain, implied by the ascents and descents to
the higher and lower notes�ascents and descents composed of smaller
waves, breaking the rises and falls of the larger ones, in a mode
peculiar to each melody. And then we have, further, the alternation of
_piano_ and _forte_ passages. That these several kinds of rhythm,
characterizing æsthetic expression, are not, in the common sense of the
word, artificial, but are intenser forms of an undulatory movement
habitually generated by feeling in its bodily discharge, is shown by the
fact that they are all traceable in ordinary speech; which in every
sentence has its primary and secondary emphases, and its cadence
containing a chief rise and fall complicated with subordinate rises and
falls; and which is accompanied by a more or less oscillatory action of
the limbs when the emotion is great.       Still longer undulations may
be observed by every one, in himself and in others, on occasions of
extreme pleasure or extreme pain. Note, in the first place, that pain
having its origin in bodily disorder, is nearly always perceptibly
rhythmical. During hours in which it never actually ceases, it has its
variations of intensity�fits or paroxysms; and then after these hours of
suffering there usually come hours of comparative ease. Moral pain has
the like smaller and larger waves. One possessed by intense grief does
not utter continuous moans, or shed tears with an equable rapidity; but
these signs of passion come in recurring bursts. Then after a time
during which such stronger and weaker waves of emotion alternate, there
comes a calm�a time of comparative deadness; to which again succeeds
another interval, when dull sorrow rises afresh into acute anguish, with
its series of paroxysms. Similarly in great delight, especially as
manifested by children who have its display less under control, there
are visible variations in the intensity of feeling shown�fits of
laughter and dancing about, separated by pauses in which smiles, and
other slight manifestations of pleasure, suffice to discharge the
lessened excitement.       Nor are there wanting evidences of mental
undulations greater in length than any of these�undulations which take
weeks, or months, or years, to complete themselves. We continually hear
of moods which recur at intervals. Very many persons have their epochs
of vivacity and depression. There are periods of industry following
periods of idleness; and times at which particular subjects or tastes
are cultivated with zeal, alternating with times at which they are
neglected. Respecting which slow oscillations, the only qualification to
be made is, that being affected by numerous influences, they are
comparatively irregular.

                  *       *       *       *       *

§ 98. In nomadic societies the changes of place, determined as they
usually are by exhaustion or failure of the supply of food, are
periodic; and in many cases show a recurrence answering to the seasons.
Each tribe that has become in some degree fixed in its locality, goes on
increasing, till under the pressures of unsatisfied desires, there
results migration of some part of it to a new region�a process repeated
at intervals. From such excesses of population, and such successive
waves of migration, come conflicts with other tribes; which are also
increasing and tending to diffuse themselves. This antagonism, like all
others, results not in an uniform motion, but in an intermittent one.
War, exhaustion, recoil�peace, prosperity, and renewed aggression:�see
here the alternation more or less discernible in the military activities
of both savage and civilized nations. And irregular as is this rhythm,
it is not more so than the different sizes of the societies, and the
extremely involved causes of variation in their strengths, would lead us
to anticipate.

Passing from external to internal changes, we meet with this backward
and forward movement under many forms. In the currents of commerce it is
especially conspicuous. Exchange during early times is almost wholly
carried on at fairs, held at long intervals in the chief centres of
population. The flux and reflux of people and commodities which each of
these exhibits, becomes more frequent as national development leads to
greater social activity. The more rapid rhythm of weekly markets begins
to supersede the slow rhythm of fairs. And eventually the process of
exchange becomes at certain places so active, as to bring about daily
meetings of buyers and sellers�a daily wave of accumulation and
distribution of cotton, or corn, or capital.       If from exchange we
turn to production and consumption, we see undulations, much longer
indeed in their periods, but almost equally obvious. Supply and demand
are never completely adapted to each other; but each of them from time
to time in excess, leads presently to an excess of the other. Farmers
who have one season produced wheat very abundantly, are disgusted with
the consequent low price; and next season, sowing a much smaller
quantity, bring to market a deficient crop; whence follows a converse
effect. Consumption undergoes parallel undulations that need not be
specified. The balancing of supplies between different districts, too,
entails analogous oscillations. A place at which some necessary of life
is scarce, becomes a place to which currents of it are set up from other
places where it is relatively abundant; and these currents from all
sides lead to a wave of accumulation where they meet�a glut: whence
follows a recoil�a partial return of the currents.       But the
undulatory character of these actions is perhaps best seen in the rises
and falls of prices. These, given in numerical measures which may be
tabulated and reduced to diagrams, show us in the clearest manner how
commercial movements are compounded of oscillations of various
magnitudes. The price of consols or the price of wheat, as thus
represented, is seen to undergo vast ascents and descents whose highest
and lowest points are reached only in the course of years. These largest
waves of variation are broken by others extending over periods of
perhaps many months. On these again come others having a week or two�s
duration. And were the changes marked in greater detail, we should have
the smaller undulations that take place each day, and the still smaller
ones which brokers telegraph from hour to hour. The whole outline would
show a complication like that of a vast ocean-swell, on whose surface
there rise large billows, which themselves bear waves of moderate size,
covered by wavelets, that are roughened by a minute ripple. Similar
diagrammatic representations of births, marriages, and deaths, of
disease, of crime, of pauperism, exhibit involved conflicts of
rhythmical motions throughout society under these several aspects.

There are like characteristics in social changes of a more complex kind.
Both in England and among continental nations, the action and reaction
of political progress have come to be generally recognized. Religion,
besides its occasional revivals of smaller magnitude, has its long
periods of exaltation and depression�generations of belief and
self-mortification, following generations of indifference and laxity.
There are poetical epochs, and epochs in which the sense of the
beautiful seems almost dormant. Philosophy, after having been awhile
predominant, lapses for a long season into neglect; and then again
slowly revives. Each science has its eras of deductive reasoning, and
its eras when attention is chiefly directed to collecting and
colligating facts. And how in such minor but more obtrusive phenomena as
those of fashion, there are ever going on oscillations from one extreme
to the other, is a trite observation.

As may be foreseen, social rhythms well illustrate the irregularity that
results from combination of many causes. Where the variations are those
of one simple element in national life, as the supply of a particular
commodity, we do indeed witness a return, after many involved movements,
to a previous condition�the price may become what it was before:
implying a like relative abundance. But where the action is one into
which many factors enter, there is never a recurrence of exactly the
same state. A political reaction never brings round just the old form of
things. The rationalism of the present day differs widely from the
rationalism of the last century. And though fashion from time to time
revives extinct types of dress, these always re-appear with decided
modifications.

                  *       *       *       *       *

§ 99. The universality of this principle suggests a question like that
raised in foregoing cases. Rhythm being manifested in all forms of
movement, we have reason to suspect that it is determined by some
primordial condition to action in general. The tacit implication is that
it is deducible from the persistence of force. This we shall find to be
the fact.

When the prong of a tuning-fork is pulled on one side by the finger, a
certain extra tension is produced among its cohering particles; which
resist any force that draws them out of their state of equilibrium. As
much force as the finger exerts in pulling the prong aside, so much
opposing force is brought into play among the cohering particles. Hence,
when the prong is liberated, it is urged back by a force equal to that
used in deflecting it. When, therefore, the prong reaches its original
position, the force impressed on it during its recoil, has generated in
it a corresponding amount of momentum�an amount of momentum nearly
equivalent, that is, to the force originally impressed (nearly, we must
say, because a certain portion has gone in communicating motion to the
air, and a certain other portion has been transformed into heat). This
momentum carries the prong beyond the position of rest, nearly as far as
it was originally drawn in the reverse direction; until at length, being
gradually used up in producing an opposing tension among the particles,
it is all lost. The opposing tension into which the expended momentum
has been transformed, then generates a second recoil; and so on
continually�the vibration eventually ceasing only because at each
movement a certain amount of force goes in creating atmospheric and
etherial undulations. Now it needs but to contemplate this repeated
action and reaction, to see that it is, like every action and reaction,
a consequence of the persistence of force. The force exerted by the
finger in bending the prong cannot disappear. Under what form then does
it exist? It exists under the form of that cohesive tension which it has
generated among the particles. This cohesive tension cannot cease
without an equivalent result. What is its equivalent result? The
momentum generated in the prong while being carried back to its position
of rest. This momentum too�what becomes of it? It must either continue
as momentum, or produce some correlative force of equal amount. It
cannot continue as momentum, since change of place is resisted by the
cohesion of the parts; and thus it gradually disappears by being
transformed into tension among these parts. This is re-transformed into
the equivalent momentum; and so on continuously.       If instead of
motion that is directly antagonized by the cohesion of matter, we
consider motion through space, the same truth presents itself under
another form. Though here no opposing force seems at work, and therefore
no cause of rhythm is apparent, yet its own accumulated momentum must
eventually carry the moving body beyond the body attracting it; and so
must become a force at variance with that which generated it. From this
conflict, rhythm necessarily results as in the foregoing case. The force
embodied as momentum in a given direction, cannot be destroyed; and if
it eventually disappears, it re-appears in the reaction on the retarding
body; which begins afresh to draw the now arrested mass back from its
aphelion. The only conditions under which there could be absence of
rhythm�the only conditions, that is, under which there could be a
continuous motion through space in the same straight line for ever,
would be the existence of an infinity void of everything but the moving
body. And neither of these conditions can be represented in thought.
Infinity is inconceivable; and so also is a motion which never had a
commencement in some pre-existing source of power.       Thus, then,
rhythm is a necessary characteristic of all motion. Given the
coexistence everywhere of antagonist forces�a postulate which, as we
have seen, is necessitated by the form of our experience�and rhythm is
an inevitable corollary from the persistence of force.

Hence, throughout that re-arrangement of parts which constitutes
Evolution, we must nowhere expect to see the change from one position of
things to another, effected by continuous movement in the same
direction. Be it in that kind of Evolution which the inorganic creation
presents, or in that presented by the organic creation, we shall
everywhere find a periodicity of action and reaction�a backward and
forward motion, of which progress is a differential result.

-----

Footnote 15:

  After having for some years supposed myself alone in the belief that
  all motion is rhythmical, I discovered that my friend Professor
  Tyndall also held this doctrine.




                              CHAPTER XII.
                 THE CONDITIONS ESSENTIAL TO EVOLUTION.


§ 100. One more preliminary is needful before proceeding. We have still
to study the conditions under which alone, Evolution can take place.

The process to be interpreted is, as already said, a certain change in
the arrangement of parts. That increase of heterogeneity commonly
displayed throughout Evolution, is not an increase in the number of
kinds of ultimate or undecomposable units which an aggregate contains;
but it is a change in the distribution of such units. If it be assumed
that what we call chemical elements, are absolutely simple (which is,
however, an hypothesis having no better warrant than the opposite one);
then it must be admitted that in respect to the number of kinds of
matter contained in it, the Earth is not more heterogeneous at present
than it was at first�that in this respect, it would be as heterogeneous
were all its undecomposable parts uniformly mixed, as it is now, when
they are arranged and combined in countless different ways. But the
increase of heterogeneity with which we have to deal, and of which alone
our senses can take cognizance, is that produced by the passage from
unity of distribution to variety of distribution. Given an aggregate
consisting of several orders of primitive units that are unchangeable;
then, these units may be so uniformly dispersed among each other, that
any portion of the mass shall be like any other portion in its sensible
properties; or they may be so segregated, simply and in endless
combinations, that the various portions of the mass shall not be like
each other in their sensible properties. A transformation of one of
these arrangements into the other, is that which constitutes Evolution.
We have to analyze the process through which structural uniformity
becomes structural multiformity�to ascertain how the originally equal
relations of position among the mixed units, pass into relations of
position that are more and more unequal, and more and more numerous in
their kinds of inequality; and how this takes place throughout all the
ascending grades of compound units, until we come even to those of which
societies are made up.

Change in the relations of position among the component units, simple or
complex, being the phenomenon we have to interpret; we must first
inquire what are the circumstances which prevent its occurrence, and
what are the circumstances which facilitate it.

                  *       *       *       *       *

§ 101. The constituents of an aggregate cannot be re-arranged, unless
they are moveable: manifestly, they must not be so firmly bound together
that the incident force fails to alter their positions. No bodies are,
indeed, possessed of this absolute rigidity; since an incident force in
being propagated through a body, always produces temporary alterations
in the relative positions of its units, if not permanent alterations. It
is true also, that even permanent re-arrangements of the units may be
thus wrought throughout the interiors of comparatively dense masses,
without any outward sign: as happens with certain crystals, which, on
exposure to sunlight, undergo molecular changes so great as to alter
their planes of cleavage. Nevertheless, since total immobility of the
parts must totally negative their re-arrangement; and since that
comparative immobility which we see in very coherent matter, is a great
obstacle to re-arrangement; it is self-evident that Evolution can be
exhibited in any considerable degree, only where there is comparative
mobility of parts.       On the other hand, those definite distributive
changes which constitute Evolution, cannot be extensively or variously
displayed, where the mobility of the parts is extreme. In liquids, the
cohesion of the units is so slight that there is no permanency in their
relations of position to each other. Such re-arrangement as any incident
force generates, is immediately destroyed again by the momentum of the
constituents moved; and so, nothing but that temporary heterogeneity
seen in circulating currents, can be produced. The like still more
obviously holds of gases.       Thus, while the theoretical limits
between which Evolution is possible, are absolute immobility of parts
and absolute mobility of parts; we may say that practically, Evolution
cannot go on to any considerable extent where the mobility is very great
or very little. A few examples will facilitate the realization of this
truth.

The highest degrees of Evolution are found in semi-solid bodies, or
bodies that come midway between the two extremes specified. Even
semi-solid bodies of the inorganic class, exhibit the segregation of
mixed units with comparative readiness: witness the fact to which
attention was first drawn by Mr. Babbage, that when the pasty mixture of
ground flints and kaolin, prepared for the manufacture of porcelain, is
kept some time, it becomes gritty and unfit for use, in consequence of
the particles of silica separating themselves from the rest, and uniting
together in grains; or witness the fact known to every housewife, that
in long-kept currant-jelly the sugar takes the shape of imbedded
crystals. While throughout the immense majority of the semi-solid
bodies, namely, the organic bodies, the proclivity to a re-arrangement
of parts is so comparatively great, as to be usually taken for a
distinctive characteristic of them.       Among organic bodies
themselves, we may trace contrasts having a like significance. It is an
accepted generalization that, other things equal, the rate of Evolution
is greatest where the plasticity is most marked. In that portion of an
egg which displays the formative processes during the early stages of
incubation, the changes of arrangement are more rapid than those which
an equal portion of the body of a hatched chick undergoes. As may be
inferred from their respective powers to acquire habits and aptitudes,
the structural modifiability of a child is greater than that of an adult
man; and the structural modifiability of an adult man is greater than
that of an old man: contrasts which are accompanied by corresponding
contrasts in the densities of the tissues; since the ratio of water to
solid matter diminishes with advancing age.       The most decisive
proof, however, is furnished by those marked retardations or arrests of
organic change, that take place when the tissues suffer a great loss of
water. Certain of the lower animals, as the _Rotifera_, may be rendered
apparently lifeless by desiccation, and will yet revive when wetted: as
their substance passes from the fluid-solid to the solid state, it
ceases to be the seat of those changes which constitute functional
activity and cause structural advance; and such changes recommence as
their substance passes from the solid to the fluid-solid state.
Analogous instances occur among much higher animals. When the African
rivers which it inhabits are dried up, the _Lepidosiren_ remains torpid
in the hardened mud, until the return of the rainy season brings water.
Humboldt states that during the summer drought, the alligators of the
Pampas lie buried in a state of suspended animation beneath the parched
surface, and struggle up out of the earth as soon as it becomes humid.
Now though we have no proof that these partial arrests of vital
activity, are consequent on the reduction of the fluid-solid tissues to
a more solid form; yet their occurrence along with a cessation in the
supply of water, is reason for suspecting that this is the case. And
similarly, though in the more numerous instances where loss of water
leads to complete arrest of vital activity, we are unable to say that
the immediate cause is a stoppage of molecular changes that results from
a diminution of molecular mobility; yet it seems not improbable that
this is the rationale of death by thirst.

Probably few will expect to find this same condition to Evolution,
illustrated in aggregates so widely different in kind as societies. Yet
even here it may be shown that no considerable degree of Evolution is
exhibited, where there is either great mobility of the parts, or great
immobility of them. In such tribes as those inhabiting Australia, we see
extremely little cohesion among the units: there is neither that partial
fixity of relative positions which results from the commencement of
agriculture, nor that partial fixity of relative positions implied by
the establishment of social grades. And along with this want of
cohesion, we find an absence of permanent differentiations. Conversely,
in societies of the oriental type, where accumulated traditions, laws,
and usages, and long-fixed class-arrangements, exercise great
restraining power over individual actions, we find Evolution almost
stopped. Through the medium of institutions and opinions, the forces
brought to bear on each unit by the rest, are so great as to prevent the
units from sensibly yielding to forces tending to re-arrange them. The
condition most favourable to increase of social heterogeneity, is a
medium coherence among the parts�a moderate facility of change in the
relations of citizens, joined with a moderate resistance to such
change�a considerable freedom of individual actions, qualified by a
considerable restraint over individual actions�a certain attachment to
pre-established arrangements, and a certain readiness to be impelled by
new influences into new arrangements�a compromise between fixity and
unfixity such as that which we, perhaps as much as any nation, exhibit.

                  *       *       *       *       *

§ 102. Another condition to Evolution, of the same order as the last
though of a different genus, must be noted. We have found that permanent
re-arrangement among the units of an aggregate, can take place only when
they have neither extreme immobility nor extreme mobility. The mobility
and immobility thus far considered (at least in all aggregates except
social ones) are those due to mechanical cohesion. There is, however,
what we must call chemical cohesion, which also influences the mobility
of the units, and consequently the re-arrangement of them. Manifestly,
if two or more kinds of units contained in any aggregate, are united by
powerful affinities, an incident force, failing to destroy their
cohesions, will not cause such various re-arrangements as it would,
could it produce new chemical combinations as well as new mechanical
adjustments. On the other hand, chemical affinities that are easily
overcome, must be favourable to multiplied re-arrangements of the units.

This condition, as well as the preceding one, is fulfilled in the
highest degree, by those aggregates which most variously display the
transformation of the uniform into the multiform. Organic bodies are on
the average distinguished from inorganic bodies, by the readiness with
which the compounds they consist of undergo decomposition, and
recomposition: the chemical cohesions of their components are so
comparatively small, that small incident forces suffice to overcome them
and cause transpositions of the components. Further, between the two
great divisions of organisms, we find a contrast in the degree of
Evolution co-existing with a contrast in the degree of chemical
modifiability. As a class, the nitrogenous compounds are peculiarly
unstable; and, speaking generally, these are present in much larger
quantities in animal tissues than they are in vegetal tissues; while,
speaking generally, animals are much more heterogeneous than plants.

Under this head it may be well also to point out that, other things
equal, the structural variety which is possible in any aggregate, must
bear a relation to the number of kinds of units contained in the
aggregate. A body made up of units of one order, cannot admit of so many
different re-arrangements, as one made up of units of two orders. And
each additional order of units must increase, in a geometrical
proportion, the number of re-arrangements that may be made.

                  *       *       *       *       *

§ 103. Yet one more condition to be specified, is the state of agitation
in which the constituents of an aggregate are kept. A familiar
expedience will introduce us to this condition. When a vessel has been
filled to the brim with loose fragments, shaking the vessel causes them
to settle down into less space, so that more may be put in. And when
among these fragments, there are some of much greater specific gravity
than the rest, these will, in the course of a prolonged shaking, find
their way to the bottom. What now is the meaning of these two results,
when expressed in general terms? We have a group of units acted on by an
incident force�the attraction of the Earth. So long as these units are
not agitated, this incident force produces no changes in their relative
positions; agitate them, and immediately their loose arrangement passes
into a more compact arrangement. Again, so long as they are not
agitated, the incident force cannot separate the heavier units from the
lighter; agitate them, and immediately the heavier units begin to
segregate. By these illustrations, a rude idea will be conveyed of the
effect which vibration has in facilitating those re-arrangements which
constitute Evolution. What here happens with visible units subject to
visible oscillations, happens also with invisible units subject to
invisible oscillations.

One or two cases in which these oscillations are of mechanical origin,
may first be noted. When a bar of steel is suspended in the magnetic
meridian, and repeatedly so struck as to send vibrations through it, it
becomes magnetized: the magnetic force of the Earth, which does not
permanently affect it while undisturbed, alters its internal state when
a mechanical agitation is propagated among its particles; and the
alteration is believed by physicists, to be a molecular re-arrangement.
It may be fairly objected that this re-arrangement is hypothetical; and
did the fact stand alone, it would be of little worth. It gains
significance, however, when joined with the fact that in the same
substance, long-continued mechanical vibrations are followed by
molecular re-arrangements that are abundantly visible. A piece of iron
which, when it leaves the workshop, is fibrous in structure, will become
crystalline if exposed to a perpetual jar. Though the polar forces
mutually exercised by the atoms, fail to change their disorderly
arrangement into an orderly arrangement while the atoms are relatively
quiescent, these forces produce this change when the atoms are kept in a
state of intestine disturbance.

But the effects which visible oscillations and oscillations sensible to
touch, have in facilitating the re-arrangement of parts by an incident
force, are insignificant compared with the effects which insensible
oscillations have in aiding such change of structure. It is a doctrine
now generally accepted among men of science, that the particles of
tangible matter, as well as the particles of ether, undulate. As
interpreted in conformity with this doctrine, the heat of a body is
simply its state of molecular motion. A mass which feels cold, is one
having but slight molecular motion, and conveying but slight molecular
motion to the surrounding medium or to the hand touching it. A mass hot
enough to radiate a sensible warmth, is one of which the more violently
agitated molecules, communicate increased undulations to the surrounding
ethereal medium; while the burn inflicted by it on the skin, is the
expression of increased undulations of the organic molecules. Such
further heat as produces softening and a consequent distortion of the
mass, is an agitation so much augmented that the units can no longer
completely maintain their relative positions. Fusion is an agitation so
extreme, that the relative positions of the units are changeable with
ease. When, finally, at a still higher temperature, the liquid is
transformed into a gas, the explanation is, that the oscillations are so
violent as to overbalance that force which held the units in close
contiguity�so violent as to keep the units at those relatively great
distances apart to which they are now thrown.       Since the
establishment of the correlation between heat and motion first gave
probability to this hypothesis, it has been receiving various
confirmations�especially by recent remarkable discoveries respecting the
absorption of heat by gases. Prof. Tyndall has proved that the quantity
of heat which any gas takes up from rays of heat passing through it, has
a distinct relation to the complexity of the atoms composing the gas.
The simple gases abstract but little; the gases composed of binary atoms
abstract, say in round numbers, a hundred times as much; while the gases
composed of atoms severally containing three, four, or more simple ones,
abstract something like a thousand times as much. These differences
Prof. Tyndall regards as due to the different abilities of the different
atoms to take up, in the increase of their own undulations, those
undulations of the ethereal medium which constitute heat�an
interpretation in perfect accordance with the late results of
spectrum-analysis; which go to show that the various elementary atoms,
when in an aeriform state, intercept those luminiferous vibrations of
the ether which are in unison or harmony with their own. And since it
holds of solid as of gaseous matters, that those consisting of simple
units transmit heat far more readily than those consisting of complex
units; we get confirmation of the inference otherwise reached, that the
units of matter in whatever state of aggregation they exist, oscillate,
and that variations of temperature are variations in the amounts of
their oscillations.

Proceeding on this hypothesis, which it would be out of place here to
defend at greater length, we have now to note how the re-arrangement of
parts is facilitated by these insensible vibrations, as we have seen it
to be by sensible vibrations. One or two cases of physical
re-arrangement may first be noted.       When some molten glass is
dropped into water, and when its outside is thus, by sudden
solidification, prevented from partaking in that contraction which the
subsequent cooling of the inside tends to produce; the units are left in
such a state of tension, that the mass flies into fragments if a small
portion of it be broken off. But now, if this mass be kept for a day or
two at a considerable heat, though a heat not sufficient to alter its
form or produce any sensible diminution of hardness, this extreme
brittleness disappears: the component particles being thrown into
greater agitation, the tensile forces are enabled to re-arrange them
into a state of equilibrium. An illustration of another order is
furnished by the subsidence of fine precipitates. These sink down very
slowly from solutions that are cold; while warm solutions deposit them
with comparative rapidity. That is to say, an increase of molecular
vibration throughout the mass, allows the suspended particles to
separate more readily from the particles of fluid.       The effect of
heat on chemical re-arrangement is so familiar, that examples are
scarcely needed. Be the substances concerned gaseous, liquid, or solid,
it equally holds that their chemical unions and disunions are aided by a
rise of temperature. Affinities which do not suffice to effect the
re-arrangement of mixed units that are in a state of feeble agitation,
suffice to effect it when the agitation is raised to a certain point.
And so long as this molecular motion is not great enough to prevent
those chemical cohesions which the affinities tend to produce, increase
of it gives increased facility of chemical re-arrangement.

This condition, in common with the preceding ones, is fulfilled most
completely in those aggregates which exhibit the phenomena of Evolution
in the highest degree; namely, the organic aggregates. And throughout
the various orders and states of these, we find minor contrasts showing
the relation between amount of molecular vibration and activity of the
metamorphic changes. Such contrasts may be arranged in the several
following groups.       Speaking generally, the phenomena of Evolution
are manifested in a much lower degree throughout the vegetal kingdom
than throughout the animal kingdom; and speaking generally, the heat of
plants is less than that of animals. Among plants themselves, the
organic changes vary in rate as the temperature varies. Though light is
the agent which effects those molecular changes causing vegetal growth,
yet we see that in the absence of heat, such changes are not effected:
in winter there is enough light, but the heat being insufficient,
plant-life is suspended. That this is the sole cause of the suspension,
is proved by the fact that at the same season, plants contained in
hot-houses, where they receive even a smaller amount of light, go on
producing leaves and flowers.       A comparison of the several
divisions of the animal kingdom with each other, shows among them
parallel relations. Regarded as a whole, vertebrate animals are higher
in temperature than invertebrate ones; and they are as a whole higher in
organic activity and development. Between subdivisions of the vertebrata
themselves, like differences in the state of molecular vibration,
accompany like differences in the degree of evolution. The least
heterogeneous of the vertebrata are the fishes; and in most cases, the
heat of fishes is nearly the same as that of the water in which they
swim: only some of them being decidedly warmer. Though we habitually
speak of reptiles as cold-blooded; and though they have not much more
power than fishes of maintaining a temperature above that of their
medium; yet since their medium (which is, in the majority of cases, the
air of warm climates) is on the average warmer than the medium inhabited
by fishes, the temperature of the class of reptiles is higher than that
of the class of fishes; and we see in them a correspondingly higher
complexity. The much more active molecular agitation in mammals and
birds, is associated with a considerably greater multiformity of
structure and a very much greater vivacity. And though birds, which are
hotter blooded than mammals, do not show us a greater multiformity; yet,
judging from their apparently greater locomotive powers, we may infer
more rapid functional changes, which, equally with structural changes,
imply molecular re-arrangement.       The most instructive contrasts,
however, are those presented by the same organic aggregates at different
temperatures. Thus we see that ova undergoing development, must be kept
more or less warm�that in the absence of a certain molecular vibration,
the re-arrangement of parts does not go on. We see, again, that in
hybernating animals, loss of heat carried to a particular point, results
in extreme retardation of the organic changes. Yet further, we see that
in animals which do not hybernate, as in man, prolonged exposure to
extreme cold, produces an irresistible tendency to sleep (which implies
a lowering of the functional activity); and then, if the abstraction of
heat continues, this sleep ends in death, or arrest of functional
activity. Lastly, we see that when the temperature is lowered till the
contained water solidifies, there is a stoppage not only of those
molecular re-arrangements which constitute life and development, but
also of those molecular re-arrangements which constitute decomposition.

Evidently then, both sensible and insensible agitations among the
components of an aggregate, facilitate any re-distributions to which
there may be a tendency. When that rhythmic change in the relative
positions of the units which constitutes vibration, is considerable, the
relative positions of the units more readily undergo permanent changes
through the action of incident forces.

                  *       *       *       *       *

§ 104. These special conditions to Evolution, are clearly but different
forms of one general condition. The abstract proposition, that a
permanent re-arrangement of units is possible only when they have
neither absolute immobility nor absolute mobility with respect to each
other, we saw to be practically equivalent to the proposition, that
extreme cohesion and extreme want of cohesion among the units are
unfavourable to Evolution. Be this cohesion or want of cohesion that
which physically characterizes the matter as we ordinarily know it; be
it that cohesion or want of cohesion distinguished as chemical; or be it
that cohesion or want of cohesion consequent on the degree of molecular
vibration; matters not, in so far as the general conclusion is
concerned. Inductively as well as deductively, we find that the genesis
of such permanent changes in the relative positions of parts, as can be
effected without destroying the continuity of the aggregate, implies a
medium stability in the relative positions of the parts: be this
stability physical, chemical, or that which varies with the state of
agitation. And as might be anticipated _à priori_, it is proved _à
posteriori_, that this re-arrangement of parts goes on most actively in
those aggregates whose units are moderately influenced by all these
forces which affect their mobility.

Here also may properly be added the remark, that to effect these changes
in the relative positions of parts, the incident forces must range
within certain limits. It is wholly a question of the ratio between
those agencies which hold the units in their positions, and those
agencies which tend to change their positions. Having given intensities
in the powers that oppose re-arrangement, there need proportionate
intensities in the powers that work re-arrangement. As there must be
neither too great nor too little cohesion; so there must be neither too
little nor too great amounts of the influences antagonistic to cohesion.
While a slight mechanical strain produces no lasting alterations in the
relative positions of parts, an excessive mechanical strain causes
disruption�causes so great an alteration in the relative positions of
parts as to destroy their union in one aggregate. While a very feeble
chemical affinity brought to bear on the associated units, fails to work
any re-arrangement of them; a chemical affinity that is extremely
intense, destroys their structural continuity, and reduces such complex
re-arrangements as have been made, to comparatively simple ones. And
while in the absence of adequate thermal undulations, the units have not
freedom enough to obey the re-arranging influences impressed on them,
the incidence of violent thermal undulations gives them such extreme
freedom that they break their connexions, and the aggregate lapses into
a liquid or gaseous form.

On the one hand, therefore, the statical forces which uphold the state
of aggregation must not be so great as wholly to prevent those changes
of relative position among the units which the dynamical forces tend to
produce; and, on the other hand, the dynamical forces must not be so
great as wholly to overcome the statical forces, and destroy the state
of aggregation. The excess of the dynamical forces must be sufficient to
produce Evolution, but not sufficient to produce Dissolution.

                  *       *       *       *       *

§ 105. And now we are naturally introduced to a consideration which,
though it does not come quite within the limits of this chapter as
expressed in its title, may yet be more conveniently dealt with here
than elsewhere. Hitherto we have studied the metamorphosis of things,
only as exhibited in the changed distribution of matter. It remains to
look at it as exhibited in the changed distribution of motion. The
definition of Evolution in its material aspect, has to be supplemented
by a definition of Evolution in its dynamical aspect.

On inquiring the source of the sensible motions seen in every kind of
Evolution, we find them all traceable to insensible motions; either of
that tangible matter which we perceive as constituting the objects
around us, or of that intangible matter which we infer as occupying
space. A brief reconsideration of the facts will make this obvious.
      The formation of celestial bodies, supposing it caused by the
union of dispersed units, must, from the beginning, have involved a
diminished motion of these units with respect to each other; and such
motion as each resulting body acquired, must previously have existed in
the motions of its units. If concrete matter has arisen by the
aggregation of diffused matter, then concrete motion has arisen by the
aggregation of diffused motion. That which now exists as the movement of
masses, implies the cessation of an equivalent molecular movement.
      Those transpositions of matter which constitute geological
changes, are clearly referable to the same source. As before shown, the
denudation of lands and deposit of new strata, are effected by water in
the course of its descent from the clouds to the sea, or during the
arrest of those undulations produced on it by winds; and, as before
shown, the elevation of water to the height whence it fell, is due to
solar heat, as is also the genesis of those aerial currents which drift
it about when evaporated and agitate its surface when condensed. That is
to say, the molecular motion of the etherial medium, is transformed into
the motion of gases, thence into the motion of liquids, and thence into
the motion of solids�stages in each of which, successively, a certain
amount of molecular motion is lost and an equivalent motion of masses
produced.       If we seek the origin of vital movements, we soon reach
a like conclusion. The actinic rays issuing from the Sun, enable the
plant to reduce special elements existing in gaseous combination around
it, to a solid form,�enable the plant, that is, to grow and carry on its
functional changes. And since growth, equally with circulation of sap,
is a mode of sensible motion, while those rays which have been expended
in generating it consist of insensible motions, we have here, too, a
transformation of the kind alleged. Animals, derived as their forces
are, directly or indirectly, from plants, carry this transformation a
step further. The automatic movements of the viscera, together with the
voluntary movements of the limbs and body at large, arise at the expense
of certain molecular movements throughout the nervous and muscular
tissues; and these originally arose at the expense of certain other
molecular movements propagated by the Sun to the Earth; so that both the
structural and functional motions which organic Evolution displays, are
motions of aggregates generated by the arrested motions of units.
      Even with the aggregates of these aggregates the same rule holds.
For among associated men, the progress is ever towards a merging of
individual actions in the actions of corporate bodies. An undeveloped
society is composed of members between whom there is little concert:
they fulfil their several wants without mutual aid; and only on
occasions of aggression or defence, act together�occasions on which
their combination, small as it is in extent, frequently fails because it
is so imperfect. In the course of civilization, however, co-operation
becomes step by step more decided. As tribes grow into nations, there
result larger aggregates, each of which has a joint political life�a
common policy and movement with respect to other aggregates. Legislative
and administrative progress, involves an increase in the number of
restraining agents brought into united and simultaneous action. In
military organization, we see an advance from small undisciplined hordes
of armed men, to vast bodies of regular troops, so drilled that the
movements of the units are entirely subordinated to the movements of the
masses. Nor does industrial development fail to show parallel changes.
Beginning with independent workers, and passing step by step to the
employment of several assistants by one master, there has ever been, and
still is, a progress towards the co-operation of greater masses of
labourers in the same establishment, and towards the union of
capitalists into more numerous and larger companies: in both which kinds
of combined action, equivalent amounts of individual action disappear.
      Under all its forms, then, Evolution, considered dynamically, is a
decrease in the relative movements of parts, and an increase in the
relative movements of wholes�using the words parts and wholes in their
widest senses. From the infinitesimal motions of those infinitesimal
units composing the etherial medium, to the larger though still
insensible motions of the larger though still insensible units composing
gaseous, fluid, and solid matter, and thence to the visible motions of
visible aggregates, the advance is from molecular motion to the motion
of masses.

But now what of the converse process? If the foregoing proposition is
true, then a change from the motion of masses to molecular motion, is
the opposite to Evolution�is Dissolution. Is this so?       Of inorganic
dissolution we have but little experience; or at least, our experience
of it is on too small a scale to exhibit it as the antithesis of
Evolution. We know, indeed, that when solids are dissolved in liquids,
their dissolution implies increased movements of their units, at the
expense of diminished movements among the units of their solvents; and
we know that when a liquid evaporates, its dissipation or dissolution
similarly implies greater relative movements of the units, and decrease
of such combined movement as they before had. But since these small
aggregates of inorganic matter, do not exhibit the phenomena of
Evolution, save in the form of simple integration; so they do not
exhibit the phenomena of dissolution, save in the form of simple
disintegration.       Of organic dissolution, however, our experience
suffices to show that it is a decrease of combined motion, and an
increase in the motion of uncombined parts. The gradual cessation of
functions, vegetal or animal, is a cessation of the sensible movements
of fluids and solids. In animals, the impulsions of the body from place
to place, first cease; presently the limbs cannot be stirred; later
still the respiratory actions stop; finally the heart becomes
stationary, and, with it, the circulating fluids. That is, the
transformation of molecular motion into the motion of masses, comes to
an end. What next takes place? We cannot say that sensible movements are
transformed into insensible movements; for sensible movements no longer
exist. Nevertheless, the process of decay involves an increase of
insensible movements; since this is far greater in the gases generated
by decomposition, than it is in the fluid-solid matters generating them.
Indeed, it might be contended that as, during Dissolution, there is a
change from the vibration of large compound atoms to the vibration of
small and comparatively simple ones, the process is strictly
antithetical to that of Evolution. In conformity with the now current
conception lately explained, each of the highly complex chemical units
composing an organic body, possesses a rhythmic movement�a movement in
which its many component units jointly partake. When decomposition
breaks up these highly complex atoms, and their constituents assume a
gaseous form, there is both an increase of molecular motion implied by
the diffusion, and a further increase implied by the resolving of such
motions as the aggregate atoms possessed, into motions of their
constituent atoms. So that in organic dissolution we have, first, an end
put to that transformation of the motion of units into the motion of
aggregates, which constitutes Evolution, dynamically considered; and we
have also, though in a subtler sense, a transformation of the motion of
aggregates into the motion of units.       The formula equally applies
to the dissolution of a society. When social ties, be they governmental
or industrial, are destroyed, the combined actions of citizens lapse
into uncombined actions. Those general forces which restrained
individual doings, having disappeared, the only remaining restraints are
those separately exercised by individuals on each other. There are no
longer any of the joint operations by which men satisfy their wants;
and, in so far as they can, they satisfy their wants by separate
operations. That is to say, the movement of parts replaces the movement
of wholes.

Under its dynamical aspect then, Evolution, so far as we can trace it,
is a change from molecular motion to the motion of masses; while
Dissolution, so far as we can trace it, is a change from the motion of
masses to molecular motion.

                  *       *       *       *       *

§ 106. To these abstract definitions may be added concrete ones. Besides
an integration of motions corresponding to the integration of masses,
Evolution involves an increase in the multiformity of the motions,
corresponding to the increase in the multiformity of the masses. If,
contemplating it as materially displayed, we find Evolution to consist
in the change from an indefinite, homogeneous distribution of parts to a
definite, heterogeneous distribution of parts; then, contemplating
Evolution as dynamically displayed, it consists in a change from
indefinite, homogeneous motions to definite, heterogeneous motions.

This change takes place under the form of an increased variety of
rhythms. We have already seen that all motion is rhythmical, from the
infinitesimal vibrations of infinitesimal molecules, up to those vast
oscillations between perihelion and aphelion performed by vast celestial
bodies. And as the contrast between these extreme cases suggests, a
multiplication of rhythms must accompany a multiplication in the degrees
and modes of aggregation, and in the relations of the aggregated masses
to incident forces. The degree or mode of aggregation will not, indeed,
affect the rate or extent of rhythm where the incident force increases
as the aggregate increases, which is the case with gravitation: here the
only cause of variation in rhythm, is difference of relation to the
incident forces; as we see in a pendulum, which, though unaffected in
its movements by a change in the weight of the bob, alters its rate of
oscillation when taken to the equator. But in all cases where the
incident forces do not vary as the masses, every new order of
aggregation initiates a new order of rhythm: witness the conclusion
drawn from the recent researches into radiant heat and light, that the
atoms of different gases have different rates of undulation. So that
increased multiformity in the arrangement of matter, has necessarily
generated increased multiformity of rhythm; both through increased
variety in the sizes and forms of aggregates, and through increased
variety in their relations to the forces which move them.       The
advancing heterogeneity of motion, thus entailed by advancing
heterogeneity in the distribution of matter, does not, however, end
here. Besides multiplication in the kinds of rhythm, there is a
progressing complexity in their combinations. As there arise wholes
composed of heterogeneous parts, each of which has its own rhythm, there
must arise compound rhythms proportionately heterogeneous. We before saw
that this is visible even in the cyclical perturbations of the Solar
System�simple as are its structure and movements. And when we
contemplate highly-developed organic bodies, we find the complication of
rhythms so great, that it defies definite analysis, and from moment to
moment works out in resultants that are incalculable.

This conception of Evolution forms a needful complement to that on which
we have hitherto chiefly dwelt. To comprehend the phenomena in their
entirety, we have to contemplate both the increasing multiformity of
parts, and the increasing multiformity of the actions simultaneously
assumed by these parts. At the same time that there are differentiations
and integrations of the matter, there are differentiations and
integrations of its motion. And this increasingly heterogeneous
distribution of motion, constitutes Evolution _functionally_ considered;
as distinguished from that increasingly heterogeneous distribution of
matter, which constitutes Evolution _structurally_ considered. While of
course, Dissolution exhibits the transition to a reverse distribution,
both structurally and functionally.

                  *       *       *       *       *

§ 107. One other preliminary must be set down. When specifically
interpreting Evolution, we shall have to consider under their concrete
forms, the various resolutions of force that follow its conflict with
matter. Here it will be well to contemplate such resolutions under their
most general or abstract forms.

Any incident force is primarily resolvable or divisible into its
_effective_ and _non-effective_ portions. In mechanical impact, the
entire momentum of a striking body is never communicated to the body
struck: even under those most favourable conditions in which the
striking body loses all its sensible motion, there still remains with it
a portion of the original momentum, under the shape of that insensible
motion produced among its particles by the collision. Of the light or
heat falling on any mass, a part, more or less considerable, is
reflected; and only the remaining part works molecular changes in the
mass.       Next it is to be noted that the effective force, is itself
divisible into the _temporarily effective_ and the _permanently
effective_. The units of an aggregate acted on, may undergo those
rhythmical changes of relative position which constitute increased
vibration, as well as other changes of relative position which are not
from instant to instant neutralized by opposite ones. Of these, the
first, disappearing in the shape of radiating undulations, leave the
molecular arrangement as it originally was; while the second conduce to
that re-arrangement constituting Evolution.       Yet a further
distinction has to be made. The permanently effective force works out
changes of relative position of two kinds�the _insensible_ and the
_sensible_. The insensible transpositions among the units are those
constituting what we call chemical composition and decomposition; and it
is these which we recognize as the qualitative differences that arise in
an aggregate. The sensible transpositions are such as result when
certain of the units, instead of being put into different relations with
their immediate neighbours, are carried away from them and united
together elsewhere.

Concerning these divisions and sub-divisions of any force affecting an
aggregate, the fact which it chiefly concerns us to observe, is, that
they are complementary to each other. Of the whole incident force, the
effective must be that which remains after deducting the non-effective.
The two parts of the effective force must vary inversely as each other:
where much of it is temporarily effective, little of it can be
permanently effective; and _vice versâ_. Lastly, the permanently
effective force, being expended in working both the insensible
re-arrangements which constitute chemical modification, and the sensible
re-arrangements which result in structure, must generate of either kind
an amount that is great or small in proportion as it has generated a
small or great amount of the other.

                  *       *       *       *       *

§ 108. And now of the propositions grouped together in this chapter, it
may be well to remark that, in common with foregoing propositions, they
have for their warrant the fundamental truth with which our synthesis
set out.

That when a given force falls on any aggregate, the permanently
effective part of it will produce an amount of re-arrangement that is
inversely proportional to the cohesion existing among the parts of the
aggregate, is demonstrable _à priori_. Whether the cohesion be
mechanical or chemical, or whether it be temporarily modified by a
changed degree of molecular vibration, matters not to the general
conclusion. In all these cases it follows from the persistence of force,
that in proportion as the units offer great resistance to alteration in
their relative positions, must the amount of motion which a given force
impresses on them be small. The proposition is in fact an identical one;
since the cohesion of units is known to be great or small, only by the
smallness or greatness of the re-arrangement which a given incident
force produces.

The continuity of motion we found to be a corollary from the persistence
of force; and from the continuity of motion, it follows that molecular
motion and the motion of masses can be respectively increased only at
each other�s expense. Hence, if in the course of Evolution there arises
a motion of masses that did not before exist, there must have ceased an
equivalent molecular motion; and if in the course of Dissolution there
arises a molecular motion that did not before exist, an equivalent
motion of masses must have disappeared.

Equally necessary is the conclusion that the several results of the
force expended on any aggregate, must be complementary to each other. It
is not less obviously a corollary from the persistence of force, that of
the whole incident force the effective is the part which remains after
deducting the non-effective; than it is, that of the effective force,
whatever does not work permanent results, works temporary results, and
that such amount of the permanently effective force as is not absorbed
in producing insensible re-arrangements, will produce sensible
re-arrangements.




                             CHAPTER XIII.
                THE INSTABILITY OF THE HOMOGENEOUS.[16]


§ 109. Thus far our steps towards the interpretation of Evolution have
been preparatory. We have dealt with the factors of the process, rather
than the process itself. After the ultimate truth that, Matter, Motion,
and Force, as cognizable by human intelligence, can neither come into
existence nor cease to exist, we have considered certain other ultimate
truths concerning the modes in which Force and Motion are manifested
during the changes they produce in Matter. Now we have to study the
changes themselves. We have here to analyze that re-arrangement in the
parts of Matter, which occurs under the influence of Force, that is
unchangeable in quantity though changeable in form, through the medium
of Motion taking place rhythmically along lines of least resistance. The
proposition which comes first in logical order, is, that some
re-arrangement must result; and this proposition may be best dealt with
under the more specific shape, that the condition of homogeneity is a
condition of unstable equilibrium.

First, as to the meaning of the terms; respecting which some readers may
need explanation. The phrase _unstable equilibrium_ is one used in
mechanics to express a balance of forces of such kind, that the
interference of any further force, however minute, will destroy the
arrangement previously subsisting; and bring about a totally different
arrangement. Thus, a stick poised on its lower end is in unstable
equilibrium: however exactly it may be placed in a perpendicular
position, as soon as it is left to itself it begins, at first
imperceptibly, to lean on one side, and with increasing rapidity falls
into another attitude. Conversely, a stick suspended from its upper end
is in stable equilibrium: however much disturbed, it will return to the
same position. The proposition is, then, that the state of homogeneity,
like the state of the stick poised on its lower end, is one that cannot
be maintained. Let us take a few illustrations.

Of mechanical ones the most familiar is that of the scales. If they be
accurately made, and not clogged by dirt or rust, it is impossible to
keep a pair of scales perfectly balanced: eventually one scale will
descend and the other ascend�they will assume a heterogeneous relation.
Again, if we sprinkle over the surface of a fluid a number of
equal-sized particles, having an attraction for each other, they will,
no matter how uniformly distributed, by and by concentrate irregularly
into one or more groups. Were it possible to bring a mass of water into
a state of perfect homogeneity�a state of complete quiescence, and
exactly equal density throughout�yet the radiation of heat from
neighbouring bodies, by affecting differently its different parts, would
inevitably produce inequalities of density and consequent currents; and
would so render it to that extent heterogeneous. Take a piece of red-hot
matter, and however evenly heated it may at first be, it will quickly
cease to be so: the exterior, cooling faster than the interior, will
become different in temperature from it. And the lapse into
heterogeneity of temperature, so obvious in this extreme case, takes
place more or less in all cases.       The action of chemical forces
supplies other illustrations. Expose a fragment of metal to air or
water, and in course of time it will be coated with a film of oxide,
carbonate, or other compound: that is�its outer parts will become unlike
its inner parts. Usually the heterogeneity produced by the action of
chemical forces on the surfaces of masses, is not striking; because the
changed portions are soon washed away, or otherwise removed. But if this
is prevented, comparatively complex structures result. Quarries of
trap-rock contain some striking examples. Not unfrequently a piece of
trap may be found reduced, by the action of the weather, to a number of
loosely-adherent coats, like those of an onion. Where the block has been
quite undisturbed, we may trace the whole series of these, from the
angular, irregular outer one, through successively included ones in
which the shape becomes gradually rounded, ending finally in a spherical
nucleus. On comparing the original mass of stone with this group of
concentric coats, each of which differs from the rest in form, and
probably in the state of decomposition at which it has arrived, we get a
marked illustration of the multiformity to which, in lapse of time, a
uniform body may be brought by external chemical action.       The
instability of the homogeneous is equally seen in the changes set up
throughout the interior of a mass, when it consists of units that are
not rigidly bound together. The atoms of a precipitate never remain
separate, and equably distributed through the fluid in which they make
their appearance. They aggregate either into crystalline grains, each
containing an immense number of atoms, or they aggregate into flocculi,
each containing a yet larger number; and where the mass of fluid is
great, and the process prolonged, these flocculi do not continue
equidistant, but break up into groups. That is to say, there is a
destruction of the balance at first subsisting among the diffused
particles, and also of the balance at first subsisting among the groups
into which these particles unite.       Certain solutions of
non-crystalline substances in highly volatile liquids, exhibit in the
course of half an hour a whole series of changes that are set up in the
alleged way. If for example a little shell-lac-varnish (made by
dissolving shell-lac in coal-naphtha until it is of the consistence of
cream) be poured on a piece of paper, the surface of the varnish will
shortly become marked by polygonal divisions, which, first appearing
round the edge of the mass, spread towards its centre. Under a lense
these irregular polygons of five or more sides, are seen to be severally
bounded by dark lines, on each side of which there are light-coloured
borders. By the addition of matter to their inner edges, the borders
slowly broaden, and thus encroach on the areas of the polygons; until at
length there remains nothing but a dark spot in the centre of each. At
the same time the boundaries of the polygons become curved; and they end
by appearing like spherical sacs pressed together; strangely simulating
(but only simulating) a group of nucleated cells. Here a rapid loss of
homogeneity is exhibited in three ways:�First, in the formation of the
film, which is the seat of these changes; second, in the formation of
the polygonal sections into which this film divides; and third, in the
contrast that arises between the polygonal sections round the edge,
where they are small and early formed, and those in the centre which are
larger and formed later.

The instability thus variously illustrated is obviously consequent on
the fact, that the several parts of any homogeneous aggregation are
necessarily exposed to different forces�forces that differ either in
kind or amount; and being exposed to different forces they are of
necessity differently modified. The relations of outside and inside, and
of comparative nearness to neighbouring sources of influence, imply the
reception of influences that are unlike in quantity or quality, or both;
and it follows that unlike changes will be produced in the parts thus
dissimilarly acted upon.

For like reasons it is manifest that the process must repeat itself in
each of the subordinate groups of units that are differentiated by the
modifying forces. Each of these subordinate groups, like the original
group, must gradually, in obedience to the influences acting upon it,
lose its balance of parts�must pass from a uniform into a multiform
state. And so on continuously.       Whence indeed it is clear that not
only must the homogeneous lapse into the non-homogeneous, but that the
more homogeneous must tend ever to become less homogeneous. If any given
whole, instead of being absolutely uniform throughout, consist of parts
distinguishable from each other�if each of these parts, while somewhat
unlike other parts, is uniform within itself; then, each of them being
in unstable equilibrium, it follows that while the changes set up within
it must render it multiform, they must at the same time render the whole
more multiform than before. The general principle, now to be followed
out in its applications, is thus somewhat more comprehensive than the
title of the chapter implies. No demurrer to the conclusions drawn, can
be based on the ground that perfect homogeneity nowhere exists; since,
whether that state with which we commence be or be not one of perfect
homogeneity, the process must equally be towards a relative
heterogeneity.

                  *       *       *       *       *

§ 110. The stars are distributed with a three-fold irregularity. There
is first the marked contrast between the plane of the milky way and
other parts of the heavens, in respect of the quantities of stars within
given visual areas. There are secondary contrasts of like kind in the
milky way itself, which has its thick and thin places; as well as
throughout the celestial spaces in general, which are much more closely
strewn in some regions than in others. And there is a third order of
contrasts produced by the aggregation of stars into small clusters.
Besides this heterogeneity of distribution of the stars in general,
considered without distinction of kinds, a further such heterogeneity is
disclosed when they are classified by their differences of colour, which
doubtless answer to differences of physical constitution. While the
yellow stars are found in all parts of the heavens, the red and blue
stars are not so: there are wide regions in which both red and blue
stars are rare; there are regions in which the blue occur in
considerable numbers, and there are other regions in which the red are
comparatively abundant. Yet one more irregularity of like significance
is presented by the nebulæ,�aggregations of matter which, whatever be
their nature, most certainly belong to our sidereal system. For the
nebulæ are not dispersed with anything like uniformity; but are abundant
around the poles of the galactic circle and rare in the neighbourhood of
its plane.       No one will expect that anything like a definite
interpretation of this structure can be given on the hypothesis of
Evolution, or any other hypothesis. The most that can be looked for is
some reason for thinking that irregularities, not improbably of these
kinds, would occur in the course of Evolution, supposing it to have
taken place. Any one called on to assign such reason might argue, that
if the matter of which stars and all other celestial bodies consist, be
assumed to have originally existed in a diffused form throughout a space
far more vast even than that which our sidereal system now occupies, the
instability of the homogeneous would negative its continuance in that
state. In default of an absolute balance among the forces with which the
dispersed particles acted on each other (which could not exist in any
aggregation having limits) he might show that motion and consequent
changes of distribution would necessarily result. The next step in the
argument would be that in matter of such extreme tenuity and feeble
cohesion there would be motion towards local centres of gravity, as well
as towards the general centre of gravity; just as, to use a humble
illustration, the particles of a precipitate aggregate into flocculi at
the same time that they sink towards the earth. He might urge that in
the one case as in the other, these smallest and earliest local
aggregations must gradually divide into groups, each concentrating to
its own centre of gravity,�a process which must repeat itself on a
larger and larger scale. In conformity with the law that motion once set
up in any direction becomes itself a cause of subsequent motion in that
direction, he might further infer that the heterogeneities thus set up
would tend ever to become more pronounced. Established mechanical
principles would justify him in the conclusion that the motions of these
irregular masses of slightly aggregated nebular matter towards their
common centre of gravity must be severally rendered curvelinear, by the
resistance of the medium from which they were precipitated; and that in
consequence of the irregularities of distribution already set up, such
conflicting curvelinear motions must, by composition of forces, end in a
rotation of the incipient sidereal system. He might without difficulty
show that the resulting centrifugal force must so far modify the process
of general aggregation, as to prevent anything like uniform distribution
of the stars eventually formed�that there must arise a contrast such as
we see between the galactic circle and the rest of the heavens. He might
draw the further not unwarrantable inference, that differences in the
process of local concentration would probably result from the unlikeness
between the physical conditions existing around the general axis of
rotation and those existing elsewhere. To which he might add, that after
the formation of distinct stars, the ever-increasing irregularities of
distribution due to continuance of the same causes would produce that
patchiness which distinguishes the heavens in both its larger and
smaller areas.       We need not here however commit ourselves to such
far-reaching speculations. For the purposes of the general argument it
is needful only to show, that any finite mass of diffused matter, even
though vast enough to form our whole sidereal system, could not be in
stable equilibrium; that in default of absolute sphericity, absolute
uniformity of composition, and absolute symmetry of relation to all
forces external to it; its concentration must go on with an
ever-increasing irregularity; and that thus the present aspect of the
heavens is not, so far as we can judge, incongruous with the hypothesis
of a general evolution consequent on the instability of the homogeneous.

Descending to that more limited form of the nebular hypothesis which
regards the solar system as having resulted by gradual concentration;
and assuming this concentration to have advanced so far as to produce a
rotating spheroid of nebulous matter; let us consider what further
consequence the instability of the homogeneous necessitates. Having
become oblate in figure, unlike in the densities of its centre and
surface, unlike in their temperatures, and unlike in the velocities with
which its parts move round their common axis, such a mass can no longer
be called homogeneous; and therefore any further changes exhibited by it
as a whole, can illustrate the general law, only as being changes from a
more homogeneous to a less homogeneous state. Changes of this kind are
to be found in the transformations of such of its parts as are still
homogeneous within themselves. If we accept the conclusion of Laplace,
that the equatorial portion of this rotating and contracting spheroid
will at successive stages acquire a centrifugal force great enough to
prevent any nearer approach to the centre round which it rotates, and
will so be left behind by the inner parts of the spheroid in its
still-continued contraction; we shall find, in the fate of the detached
ring, a fresh exemplification of the principle we are following out.
Consisting of gaseous matter, such a ring, even if absolutely uniform at
the time of its detachment, cannot continue so. To maintain its
equilibrium there must be an almost perfect uniformity in the action of
all external forces upon it (almost, we must say, because the cohesion,
even of extremely attenuated matter, might suffice to neutralize very
minute disturbances); and against this the probabilities are immense. In
the absence of equality among the forces, internal and external, acting
on such a ring, there must be a point or points at which the cohesion of
its parts is less than elsewhere�a point or points at which rupture will
therefore take place. Laplace assumed that the ring would rupture at one
place only; and would then collapse on itself. But this is a more than
questionable assumption�such at least I know to be the opinion of an
authority second to none among those now living. So vast a ring,
consisting of matter having such feeble cohesion, must break up into
many parts. Nevertheless, it is still inferrable from the instability of
the homogeneous, that the ultimate result which Laplace predicted would
take place. For even supposing the masses of nebulous matter into which
such a ring separated, were so equal in their sizes and distances as to
attract each other with exactly equal forces (which is infinitely
improbable); yet the unequal action of external disturbing forces would
inevitably destroy their equilibrium�there would be one or more points
at which adjacent masses would begin to part company. Separation once
commenced, would with ever-accelerating speed lead to a grouping of the
masses. And obviously a like result would eventually take place with the
groups thus formed; until they at length aggregated into a single mass.

Leaving the region of speculative astronomy, let us consider the Solar
System as it at present exists. And here it will be well, in the first
place, to note a fact which may be thought at variance with the
foregoing argument�namely, the still-continued existence of Saturn�s
rings; and especially of the internal nebulous ring lately discovered.
To the objection that the outer rings maintain their equilibrium, the
reply is that the comparatively great cohesion of liquid or solid
substance would suffice to prevent any slight tendency to rupture from
taking effect. And that a nebulous ring here still preserves its
continuity, does not really negative the foregoing conclusion; since it
happens under the quite exceptional influence of those symmetrically
disposed forces which the external rings exercise on it.       Here
indeed it deserves to be noted, that though at first sight the Saturnian
system appears at variance with the doctrine that a state of homogeneity
is one of unstable equilibrium, it does in reality furnish a curious
confirmation of this doctrine. For Saturn is not quite concentric with
his rings; and it has been proved mathematically that were he and his
rings concentrically situated, they could not remain so: the homogeneous
relation being unstable, would gravitate into a heterogeneous one. And
this fact serves to remind us of the allied one presented throughout the
whole Solar System. All orbits, whether of planets or satellites, are
more or less excentric�none of them are perfect circles; and were they
perfect circles they would soon become ellipses. Mutual perturbations
would inevitably generate excentricities. That is to say, the
homogeneous relations would lapse into heterogeneous ones.

                  *       *       *       *       *

§ 111. Already so many references have been made to the gradual
formation of a crust over the originally incandescent Earth, that it may
be thought superfluous again to name it. It has not, however, been
before considered in connexion with the general principle under
discussion. Here then it must be noted as a necessary consequence of the
instability of the homogeneous. In this cooling down and solidification
of the Earth�s surface, we have one of the simplest, as well as one of
the most important, instances, of that change from a uniform to a
multiform state which occurs in any mass through exposure of its
different parts to different conditions.       To the differentiation of
the Earth�s exterior from its interior thus brought about, we must add
one of the most conspicuous differentiations which the exterior itself
afterwards undergoes, as being similarly brought about. Were the
conditions to which the surface of the Earth is exposed, alike in all
directions, there would be no obvious reason why certain of its parts
should become permanently unlike the rest. But being unequally exposed
to the chief external centre of force�the Sun�its main divisions become
unequally modified: as the crust thickens and cools, there arises that
contrast, now so decided, between the polar and equatorial regions.

Along with these most marked physical differentiations of the Earth,
which are manifestly consequent on the instability of the homogeneous,
there have been going on numerous chemical differentiations, admitting
of similar interpretation. Without raising the question whether, as some
think, the so-called simple substances are themselves compounded of
unknown elements (elements which we cannot separate by artificial heat,
but which existed separately when the heat of the Earth was greater than
any which we can produce),�without raising this question, it will
suffice the present purpose to show how, in place of that comparative
homogeneity of the Earth�s crust, chemically considered, which must have
existed when its temperature was high, there has arisen, during its
cooling, an increasing chemical heterogeneity: each element or compound,
being unable to maintain its homogeneity in presence of various
surrounding affinities, having fallen into heterogeneous combinations.
Let us contemplate this change somewhat in detail.       There is every
reason to believe that at an extreme heat, the bodies we call elements
cannot combine. Even under such heat as can be generated artificially,
some very strong affinities yield; and the great majority of chemical
compounds are decomposed at much lower temperatures. Whence it seems not
improbable that, when the Earth was in its first state of incandescence,
there were no chemical combinations at all. But without drawing this
inference, let us set out with the unquestionable fact that the
compounds which can exist at the highest temperatures, and which must
therefore have been the first formed as the Earth cooled, are those of
the simplest constitutions. The protoxides�including under that head the
alkalies, earths, &c.�are, as a class, the most fixed compounds known:
the majority of them resisting decomposition by any heat we can
generate. These, consisting severally of one atom of each component
element, are combinations of the simplest order�are but one degree less
homogeneous than the elements themselves. More heterogeneous than these,
more decomposable by heat, and therefore later in the Earth�s history,
are the deutoxides, tritoxides, peroxides, &c.; in which two, three,
four, or more atoms of oxygen are united with one atom of metal or other
base. Still less able to resist heat, are the salts; which present us
with compound atoms each made up of five, six, seven, eight, ten,
twelve, or more atoms, of three, if not more, kinds. Then there are the
hydrated salts, of a yet greater heterogeneity, which undergo partial
decomposition at much lower temperatures. After them come the
further-complicated supersalts and double salts, having a stability
again decreased; and so throughout. After making a few unimportant
qualifications demanded by peculiar affinities, I believe no chemist
will deny it to be a general law of these inorganic combinations that,
other things equal, the stability decreases as the complexity increases.
And then when we pass to the compounds that make up organic bodies, we
find this general law still further exemplified: we find much greater
complexity and much less stability. An atom of albumen, for instance,
consists of 482 ultimate atoms of five different kinds. Fibrine, still
more intricate in constitution, contains in each atom, 298 atoms of
carbon, 49 of nitrogen, 2 of sulphur, 228 of hydrogen, and 92 of
oxygen�in all, 660 atoms; or, more strictly speaking�equivalents. And
these two substances are so unstable as to decompose at quite moderate
temperatures; as that to which the outside of a joint of roast meat is
exposed. Possibly it will be objected that some inorganic compounds, as
phosphuretted hydrogen and chloride of nitrogen, are more decomposable
than most organic compounds. This is true. But the admission may be made
without damage to the argument. The proposition is not that _all_ simple
combinations are more fixed than _all_ complex ones. To establish our
inference it is necessary only to show that, as an _average fact_, the
simple combinations can exist at a higher temperature than the complex
ones. And this is wholly beyond question.       Thus it is manifest that
the present chemical heterogeneity of the Earth�s surface has arisen by
degrees as the decrease of heat has permitted; and that it has shown
itself in three forms�first, in the multiplication of chemical
compounds; second, in the greater number of different elements contained
in the more modern of these compounds; and third, in the higher and more
varied multiples in which these more numerous elements combine.

Without specifying them, it will suffice just to name the meteorologic
processes eventually set up in the Earth�s atmosphere, as further
illustrating the alleged law. They equally display that destruction of a
homogeneous state which results from unequal exposure to incident
forces.

                  *       *       *       *       *

§ 112. Take a mass of unorganized but organizable matter�either the body
of one of the lowest living forms, or the germ of one of the higher.
Consider its circumstances. Either it is immersed in water or air, or it
is contained within a parent organism. Wherever placed, however, its
outer and inner parts stand differently related to surrounding
agencies�nutriment, oxygen, and the various stimuli. But this is not
all. Whether it lies quiescent at the bottom of the water or on the leaf
of a plant; whether it moves through the water preserving some definite
attitude; or whether it is in the inside of an adult; it equally results
that certain parts of its surface are more exposed to surrounding
agencies than other parts�in some cases more exposed to light, heat, or
oxygen, and in others to the maternal tissues and their contents. Hence
must follow the destruction of its original equilibrium. This may take
place in one of two ways. Either the disturbing forces may be such as to
overbalance the affinities of the organic elements, in which case there
result those changes which are known as decomposition; or, as is
ordinarily the case, such changes are induced as do not destroy the
organic compounds, but only modify them: the parts most exposed to the
modifying forces being most modified. To elucidate this, suppose we take
a few cases.

Note first what appear to be exceptions. Certain minute animal forms
present us either with no appreciable differentiations or with
differentiations so obscure as to be made out with great difficulty. In
the Rhizopods, the substance of the jelly-like body remains throughout
life unorganized, even to the extent of having no limiting membrane; as
is proved by the fact that the thread-like processes protruded by the
mass, coalesce on touching each other. Whether or not the nearly allied
_Am�ba_, of which the less numerous and more bulky processes do not
coalesce, has, as lately alleged, something like a cell-wall and a
nucleus, it is clear that the distinction of parts is very slight; since
particles of food pass bodily into the inside through any part of the
periphery, and since when the creature is crushed to pieces, each piece
behaves as the whole did. Now these cases, in which there is either no
contrast of structure between exterior and interior or very little,
though seemingly opposed to the above inference, are really very
significant evidences of its truth. For what is the peculiarity of this
division of the _Protozoa_? Its members undergo perpetual and irregular
changes of form�they show no persistent relation of parts. What lately
formed a portion of the interior is now protruded, and, as a temporary
limb, is attached to some object it happens to touch. What is now a part
of the surface will presently be drawn, along with the atom of nutriment
sticking to it, into the centre of the mass. Either the relations of
inner and outer have no permanent existence, or they are very slightly
marked. But by the hypothesis, it is only because of their unlike
positions with respect to modifying forces, that the originally like
units of a living mass become unlike. We must therefore expect no
established differentiation of parts in creatures which exhibit no
established differences of position in their parts; and we must expect
extremely little differentiation of parts where the differences of
position are but little determined�which is just what we find.
      This negative evidence is borne out by positive evidence. When we
turn from these proteiform specks of living jelly to organisms having an
unchanging distribution of substance, we find differences of tissue
corresponding to differences of relative position. In all the higher
_Protozoa_, as also in the _Protophyta_, we meet with a fundamental
differentiation into cell-membrane and cell-contents; answering to that
fundamental contrast of conditions implied by the terms outside and
inside.       On passing from what are roughly classed as unicellular
organisms, to the lowest of those which consist of aggregated cells, we
equally observe the connection between structural differences and
differences of circumstance. Negatively, we see that in the sponge,
permeated throughout by currents of sea-water, the indefiniteness of
organization corresponds with the absence of definite unlikeness of
conditions: the peripheral and central portions are as little contrasted
in structure as in exposure to surrounding agencies. While positively,
we see that in a form like the _Thalassicolla_, which, though equally
humble, maintains its outer and inner parts in permanently unlike
circumstances, there is displayed a rude structure obviously
subordinated to the primary relations of centre and surface: in all its
many and important varieties, the parts exhibit a more or less
concentric arrangement.

After this primary modification, by which the outer tissues are
differentiated from the inner, the next in order of constancy and
importance is that by which some part of the outer tissues is
differentiated from the rest; and this corresponds with the almost
universal fact that some part of the outer tissues is more exposed to
certain environing influences than the rest. Here, as before, the
apparent exceptions are extremely significant. Some of the lowest
vegetal organisms, as the _Hematococci_ and _Protococci_, evenly
imbedded in a mass of mucus, or dispersed through the Arctic snow,
display no differentiations of surface; the several parts of their
surfaces being subjected to no definite contrasts of conditions.
Ciliated spheres such as the _Volvox_ have no parts of their periphery
unlike other parts; and it is not to be expected that they should have;
since, as they revolve in all directions, they do not, in traversing the
water, permanently expose any part to special conditions. But when we
come to organisms that are either fixed, or while moving preserve
definite attitudes, we no longer find uniformity of surface. The most
general fact which can be asserted with respect to the structures of
plants and animals, is, that however much alike in shape and texture the
various parts of the exterior may at first be, they acquire unlikenesses
corresponding to the unlikenesses of their relations to surrounding
agencies. The ciliated germ of a Zoophyte, which, during its locomotive
stage, is distinguishable only into outer and inner tissues, no sooner
becomes fixed, than its upper end begins to assume a different structure
from its lower. The disc-shaped _gemmæ_ of the _Marchantia_, originally
alike on both surfaces, and falling at random with either side
uppermost, immediately begin to develop rootlets on the under side, and
_stomata_ on the upper side: a fact proving beyond question, that this
primary differentiation is determined by this fundamental contrast of
conditions.

Of course in the germs of higher organisms, the metamorphoses
immediately due to the instability of the homogeneous, are soon masked
by those due to the assumption of the hereditary type. Such early
changes, however, as are common to all classes of organisms, and so
cannot be ascribed to heredity, entirely conform to the hypothesis. A
germ which has undergone no developmental modifications, consists of a
spheroidal group of homogeneous cells. Universally, the first step in
its evolution is the establishment of a difference between some of the
peripheral cells and the cells which form the interior�some of the
peripheral cells, after repeated spontaneous fissions, coalesce into a
membrane; and by continuance of the process this membrane spreads until
it speedily invests the entire mass, as in mammals, or, as in birds,
stops short of that for some time. Here we have two significant facts.
The first is, that the primary unlikeness arises between the exterior
and the interior. The second is, that the change which thus initiates
development, does not take place simultaneously over the whole exterior;
but commences at one place, and gradually involves the rest. Now these
facts are just those which might be inferred from the instability of the
homogeneous. The surface must, more than any other part, become unlike
the centre, because it is most dissimilarly conditioned; and all parts
of the surface cannot simultaneously exhibit this differentiation,
because they cannot be exposed to the incident forces with absolute
uniformity.       One other general fact of like implication remains.
Whatever be the extent of this peripheral layer of cells, or blastoderm
as it is called, it presently divides into two layers�the serous and
mucous; or, as they have been otherwise called, the ectoderm and the
endoderm. The first of these is formed from that portion of the layer
which lies in contact with surrounding agents; and the second of them is
formed from that portion of the layer which lies in contact with the
contained mass of yelk. That is to say, after the primary
differentiation, more or less extensive, of surface from centre, the
resulting superficial portion undergoes a secondary differentiation into
inner and outer parts�a differentiation which is clearly of the same
order with the preceding, and answers to the next most marked contrast
of conditions.

But, as already hinted, this principle, understood in the simple form
here presented, supplies no key to the detailed phenomena of organic
development. It fails entirely to explain generic and specific
peculiarities; and indeed leaves us equally in the dark respecting those
more important distinctions by which families and orders are marked out.
Why two ova, similarly exposed in the same pool, should become the one a
fish, and the other a reptile, it cannot tell us. That from two
different eggs placed under the same hen, should respectively come forth
a duckling and a chicken, is a fact not to be accounted for on the
hypothesis above developed. We have here no alternative but to fall back
upon the unexplained principle of hereditary transmission. The capacity
possessed by an unorganized germ of unfolding into a complex adult,
which repeats ancestral traits in the minutest details, and that even
when it has been placed in conditions unlike those of its ancestors, is
a capacity we cannot at present understand. That a microscopic portion
of seemingly structureless matter should embody an influence of such
kind, that the resulting man will in fifty years after become gouty or
insane, is a truth which would be incredible were it not daily
illustrated.       Should it however turn out, as we shall hereafter
find reason for suspecting, that these complex differentiations which
adults exhibit, are themselves the slowly accumulated and transmitted
results of a process like that seen in the first changes of the germ; it
will follow that even those embryonic changes due to hereditary
influence, are remote consequences of the alleged law. Should it be
shown that the slight modifications wrought during life on each adult,
and bequeathed to offspring along with all like preceding modifications,
are themselves unlikenesses of parts that are produced by unlikenesses
of conditions; then it will follow that the modifications displayed in
the course of embryonic development, are partly direct consequences of
the instability of the homogeneous, and partly indirect consequences of
it.       To give reasons for entertaining this hypothesis, however, is
not needful for the justification of the position here taken. It is
enough that the most conspicuous differentiations which incipient
organisms universally display, correspond to the most marked differences
of conditions to which their parts are subject. It is enough that the
habitual contrast between outside and inside, which we _know_ is
produced in inorganic masses by unlikeness of exposure to incident
forces, is strictly paralleled by the first contrast that makes its
appearance in all organic masses.

It remains to point out that in the assemblage of organisms
constituting a species, the principle enunciated is equally traceable.
We have abundant materials for the induction that each species will
not remain uniform, but is ever becoming to some extent multiform; and
there is ground for the deduction that this lapse from homogeneity to
heterogeneity is caused by the subjection of its members to unlike
sets of circumstances. The fact that in every species, animal and
vegetal, the individuals are never quite alike; joined with the fact
that there is in every species a tendency to the production of
differences marked enough to constitute varieties; form a sufficiently
wide basis for the induction. While the deduction is confirmed by the
familiar experience that varieties are most numerous and decided
where, as among cultivated plants and domestic animals, the conditions
of life depart from the original ones, most widely and in the most
numerous ways. Whether we regard �natural selection� as wholly, or
only in part, the agency through which varieties are established,
matters not to the general conclusion. For as the survival of any
variety proves its constitution to be in harmony with a certain
aggregate of surrounding forces�as the multiplication of a variety and
the usurpation by it of an area previously occupied by some other part
of the species, implies different effects produced by such aggregate
of forces on the two, it is clear that this aggregate of forces is the
real cause of the differentiation�it is clear that if the variety
supplants the original species in some localities but not in others,
it does so because the aggregate of forces in the one locality is
unlike that in the other�it is clear that the lapse of the species
from a state of homogeneity to a state of heterogeneity arises from
the exposure of its different parts to different aggregates of forces.

                  *       *       *       *       *

§ 113. Among mental phenomena it is difficult to establish the alleged
law without an analysis too extensive for the occasion. To show
satisfactorily how states of consciousness, originally homogeneous,
become heterogeneous through differences in the changes wrought by
different forces, would require us carefully to trace out the
organization of early experiences. Were this done it would become
manifest that the development of intelligence, is, under one of its
chief aspects, a dividing into separate classes, the unlike things
previously confounded together in one class�a formation of sub-classes
and sub-sub-classes, until the once confused aggregate of objects known,
is resolved into an aggregate which unites extreme heterogeneity among
its multiplied groups, with complete homogeneity among the members of
each group. If, for example, we followed, through ascending grades of
creatures, the genesis of that vast structure of knowledge acquired by
sight, we should find that in the first stage, where eyes suffice for
nothing beyond the discrimination of light from darkness, the only
possible classifications of objects seen, must be those based on the
manner in which light is obstructed, and the degree in which it is
obstructed. We should find that by such undeveloped visual organs, the
shadows traversing the rudimentary retina would be merely distinguished
into those of the stationary objects which the creature passed during
its own movements, and those of the moving objects which came near the
creature while it was at rest; and that so the extremely general
classification of visible things into stationary and moving, would be
the earliest formed. We should find that whereas the simplest eyes are
not fitted to distinguish between an obstruction of light caused by a
small object close to, and an obstruction caused by a large object at
some distance, eyes a little more developed must be competent to such a
distinction; whence must result a vague differentiation of the class of
moving objects, into the nearer and the more remote. We should find that
such further improvements in vision as those which make possible a
better estimation of distances by adjustment of the optic axes, and
those which, through enlargement and subdivision of the retina, make
possible the discrimination of shapes, must have the effects of giving
greater definiteness to the classes already formed, and of sub-dividing
these into smaller classes, consisting of objects less unlike. And we
should find that each additional refinement of the perceptive organs,
must similarly lead to a multiplication of divisions and a sharpening of
the limits of each division. In every infant might be traced the
analogous transformation of a confused aggregate of impressions of
surrounding objects, not recognized as differing in their distances,
sizes, and shapes, into separate classes of objects unlike each other in
these and various other respects. And in the one case as in the other,
it might be shown that the change from this first indefinite, incoherent
and comparatively homogeneous consciousness, to a definite, coherent,
and heterogeneous one, is due to differences in the actions of incident
forces on the organism.       These brief indications of what might be
shown, did space permit, must here suffice. Probably they will give
adequate clue to an argument by which each reader may satisfy himself
that the course of mental evolution offers no exception to the general
law. In further aid of such an argument, I will here add an illustration
that is comprehensible apart from the process of mental evolution as a
whole.

It has been remarked (I am told by Coleridge, though I have been unable
to find the passage) that with the advance of language, words which were
originally alike in their meanings acquire unlike meanings�a change
which he expresses by the formidable word �desynonymization.� Among
indigenous words this loss of equivalence cannot be clearly shown;
because in them the divergencies of meaning began before the dawn of
literature. But among words that have been coined, or adopted from other
languages, since the writing of books commenced, it is demonstrable. In
the old divines, _miscreant_ is used in its etymological sense of
_unbeliever_; but in modern speech it has entirely lost this sense.
Similarly with _evil-doer_ and _malefactor_: exactly synonymous as these
are by derivation, they are no longer synonymous by usage: by a
_malefactor_ we now understand a convicted criminal, which is far from
being the acceptation of _evil-doer_. The verb _produce_, bears in
Euclid its primary meaning�to _prolong_, or _draw out_; but the now
largely developed meanings of _produce_ have little in common with the
meanings of _prolong_, or _draw out_. In the Church of England liturgy,
an odd effect results from the occurrence of _prevent_ in its original
sense�_to come before_, instead of its modern specialized sense�_to come
before with the effect of arresting_. But the most conclusive cases are
those in which the contrasted words consist of the same parts
differently combined; as in _go under_ and _undergo_. We _go under_ a
tree, and we _undergo_ a pain. But though, if analytically considered,
the meanings of these expressions would be the same were the words
transposed, habit has so far modified their meanings that we could not
without absurdity speak of _undergoing_ a tree and _going under_ a pain.
      Countless such instances might be brought to show that between two
words which are originally of like force, an equilibrium cannot be
maintained. Unless they are daily used in exactly equal degrees, in
exactly similar relations (against which there are infinite
probabilities), there necessarily arises a habit of associating one
rather than the other with particular acts, or objects. Such a habit,
once commenced, becomes confirmed; and gradually their homogeneity of
meaning disappears. In each individual we may see the tendency which
inevitably leads to this result. A certain vocabulary and a certain set
of phrases, distinguish the speech of each person: each person
habitually uses certain words in places where other words are habitually
used by other persons; and there is a continual recurrence of favourite
expressions. This inability to maintain a balance in the use of verbal
symbols, which characterizes every man, characterizes, by consequence,
aggregates of men; and the desynonymization of words is the ultimate
effect.

Should any difficulty be felt in understanding how these mental changes
exemplify a law of physical transformations that are wrought by physical
forces, it will disappear on contemplating acts of mind as nervous
functions. It will be seen that each loss of equilibrium above
instanced, is a loss of functional equality between some two elements of
the nervous system. And it will be seen that, as in other cases, this
loss of functional equality is due to differences in the incidence of
forces.

                  *       *       *       *       *

§ 114. Masses of men, in common with all other masses, show a like
proclivity similarly caused. Small combinations and large societies
equally manifest it; and in the one, as in the other, both governmental
and industrial differentiations are initiated by it. Let us glance at
the facts under these two heads.

A business partnership, balanced as the authorities of its members may
theoretically be, practically becomes a union in which the authority of
one partner is tacitly recognized as greater than that of the other or
others. Though the shareholders have given equal powers to the directors
of their company, inequalities of power soon arise among them; and
usually the supremacy of some one director grows so marked, that his
decisions determine the course which the board takes. Nor in
associations for political, charitable, literary, or other purposes, do
we fail to find a like process of division into dominant and subordinate
parties; each having its leader, its members of less influence, and its
mass of uninfluential members. These minor instances in which
unorganized groups of men, standing in homogeneous relations, may be
watched gradually passing into organized groups of men standing in
heterogeneous relations, give us the key to social inequalities.
Barbarous and civilized communities are alike characterized by
separation into classes, as well as by separation of each class into
more important and less important units; and this structure is
manifestly the gradually-consolidated result of a process like that
daily exemplified in trading and other combinations. So long as men are
constituted to act on one another, either by physical force or by force
of character, the struggles for supremacy must finally be decided in
favour of some one; and the difference once commenced must tend to
become ever more marked. Its unstable equilibrium being destroyed, the
uniform must gravitate with increasing rapidity into the multiform. And
so supremacy and subordination must establish themselves, as we see they
do, throughout the whole structure of a society, from the great
class-divisions pervading its entire body, down to village cliques, and
even down to every posse of school-boys.       Probably it will be
objected that such changes result, not from the homogeneity of the
original aggregations, but from their non-homogeneity�from certain
slight differences existing among their units at the outset. This is
doubtless the proximate cause. In strictness, such changes must be
regarded as transformations of the relatively homogeneous into the
relatively heterogeneous. But it is abundantly clear that an aggregation
of men, absolutely alike in their endowments, would eventually undergo a
similar transformation. For in the absence of perfect uniformity in the
lives severally led by them�in their occupations, physical conditions,
domestic relations, and trains of thought and feeling�there must arise
differences among them; and these must finally initiate social
differentiations. Even inequalities of health caused by accidents, must,
by entailing inequalities of physical and mental power, disturb the
exact balance of mutual influences among the units; and the balance once
disturbed, must inevitably be lost. Whence, indeed, besides seeing that
a body of men absolutely homogeneous in their governmental relations,
must, like all other homogeneous bodies, become heterogeneous, we also
see that it must do this from the same ultimate cause�unequal exposure
of its parts to incident forces.

The first industrial divisions of societies are much more obviously due
to unlikenesses of external circumstances. Such divisions are absent
until such unlikenesses are established. Nomadic tribes do not
permanently expose any groups of their members to special local
conditions; nor does a stationary tribe, when occupying only a small
area, maintain from generation to generation marked contrasts in the
local conditions of its members; and in such tribes there are no decided
economical differentiations. But a community which, growing populous,
has overspread a large tract, and has become so far settled that its
members live and die in their respective districts, keeps its several
sections in different physical circumstances; and then they no longer
remain alike in their occupations. Those who live dispersed continue to
hunt or cultivate the earth; those who spread to the sea-shore fall into
maritime occupations; while the inhabitants of some spot chosen, perhaps
for its centrality, as one of periodical assemblage, become traders, and
a town springs up. Each of these classes undergoes a modification of
character consequent on its function, and better fitting it to its
function. Later in the process of social evolution these local
adaptations are greatly multiplied. A result of differences in soil and
climate, is that the rural inhabitants in different parts of the kingdom
have their occupations partially specialized; and become respectively
distinguished as chiefly producing cattle, or sheep, or wheat, or oats,
or hops, or cyder. People living where coal-fields are discovered are
transformed into colliers; Cornishmen take to mining because Cornwall is
metalliferous; and the iron-manufacture is the dominant industry where
ironstone is plentiful. Liverpool has assumed the office of importing
cotton, in consequence of its proximity to the district where cotton
goods are made; and for analogous reasons, Hull has become the chief
port at which foreign wools are brought in. Even in the establishment of
breweries, of dye-works, of slate-quarries, of brickyards, we may see
the same truth. So that both in general and in detail, the
specializations of the social organism which characterize separate
districts, primarily depend on local circumstances. Those divisions of
labour which under another aspect were interpreted as due to the setting
up of motion in the directions of least resistance (§ 91), are here
interpreted as due to differences in the incident forces; and the two
interpretations are quite consistent with each other. For that which in
each case _determines_ the direction of least resistance, is the
distribution of the forces to be overcome; and hence unlikenesses of
distribution in separate localities, entails unlikenesses in the course
of human action in those localities�entails industrial differentiations.

                  *       *       *       *       *

§ 115. In common with the general truths set forth in preceding
chapters, the instability of the homogeneous is demonstrable _à priori_.
It, like each of them, is a corollary from the persistence of force.
Already this has been tacitly implied by assigning unlikeness in the
exposure of its part to surrounding agencies, as the reason why a
uniform mass loses its uniformity. But here it will be proper to expand
this tacit implication into definite proof.

On striking a mass of matter with such force as either to indent it or
make it fly to pieces, we see both that the blow affects differently its
different parts, and that the differences are consequent on the unlike
relations of its parts to the force impressed. The part with which the
striking body comes in contact, receiving the whole of the communicated
momentum, is driven in towards the centre of the mass. It thus
compresses and tends to displace the more centrally situated portions of
the mass. These, however, cannot be compressed or thrust out of their
places without pressing on all surrounding portions. And when the blow
is violent enough to fracture the mass, we see, in the radial dispersion
of its fragments, that the original momentum, in being distributed
throughout it, has been divided into numerous minor momenta, unlike in
their directions. We see that these directions are determined by the
positions of the parts with respect to each other, and with respect to
the point of impact. We see that the parts are differently affected by
the disruptive force, because they are differently related to it in
their directions and attachments�that the effects being the joint
products of the cause and the conditions, cannot be alike in parts which
are differently conditioned.       A body on which radiant heat is
falling, exemplifies this truth still more clearly. Taking the simplest
case (that of a sphere) we see that while the part nearest to the
radiating centre receives the rays at right angles, the rays strike the
other parts of the exposed side at all angles from 90° down to 0°.
Again, the molecular vibrations propagated through the mass from the
surface which receives the heat, must proceed inwards at angles
differing for each point. Further, the interior parts of the sphere
affected by the vibrations proceeding from all points of the heated
side, must be dissimilarly affected in proportion as their positions are
dissimilar. So that whether they be on the recipient area, in the
middle, or at the remote side, the constituent atoms are all thrown into
states of vibration more or less unlike each other.

But now, what is the ultimate meaning of the conclusion that a uniform
force produces different changes throughout a uniform mass, because the
parts of the mass stand in different relations to the force? Fully to
understand this, we must contemplate each part as simultaneously subject
to other forces�those of gravitation, of cohesion, of molecular motion,
&c. The effect wrought by an additional force, must be a resultant of it
and the forces already in action. If the forces already in action on two
parts of any aggregate, are different in their directions, the effects
produced on these two parts by like forces must be different in their
directions. Why must they be different? They must be different because
such unlikeness as exists between the two sets of factors, is made by
the presence in the one of some specially-directed force that is not
present in the other; and that this force will produce an effect,
rendering the total result in the one case unlike that in the other, is
a necessary corollary from the persistence of force.       Still more
manifest does it become that the dissimilarly-placed parts of any
aggregate must be dissimilarly modified by an incident force, when we
remember that the _quantities_ of the incident force to which they are
severally subject, are not equal, as above supposed; but are nearly
always very unequal. The outer parts of masses are usually alone exposed
to chemical actions; and not only are their inner parts shielded from
the affinities of external elements, but such affinities are brought to
bear unequally on their surfaces; since chemical action sets up currents
through the medium in which it takes place, and so brings to the various
parts of the surface unequal quantities of the active agent. Again, the
amounts of any external radiant force which the different parts of an
aggregate receive, are widely contrasted: we have the contrast between
the quantity falling on the side next the radiating centre, and the
quantity, or rather no quantity, falling on the opposite side; we have
contrasts in the quantities received by differently-placed areas on the
exposed side; and we have endless contrasts between the quantities
received by the various parts of the interior. Similarly when mechanical
force is expended on any aggregate, either by collision, continued
pressure, or tension, the amounts of strain distributed throughout the
mass are manifestly unlike for unlike positions. But to say the
different parts of an aggregate receive different quantities of any
incident force, is to say that their states are modified by it in
different degrees�is to say that if they were before homogeneous in
their relations they must be rendered to a proportionate extent
heterogeneous; since, force being persistent, the different quantities
of it falling on the different parts, must work in them different
quantities of effect�different changes.       Yet one more kindred
deduction is required to complete the argument. We may, by parallel
reasoning, reach the conclusion that, even apart from the action of any
external force, the equilibrium of a homogeneous aggregate must be
destroyed by the unequal actions of its parts on each other. That mutual
influence which produces aggregation (not to mention other mutual
influences) must work different effects on the different parts; since
they are severally exposed to it in unlike amounts and directions. This
will be clearly seen on remembering that the portions of which the whole
is made up, may be severally regarded as minor wholes; that on each of
these minor wholes, the action of the entire aggregate then becomes an
external incident force; that such external incident force must, as
above shown, work unlike changes in the parts of any such minor whole;
and that if the minor wholes are severally thus rendered heterogeneous,
the entire aggregate is rendered heterogeneous.

The instability of the homogeneous is thus deducible from that
primordial truth which underlies our intelligence. One stable
homogeneity only, is hypothetically possible. If centres of force,
absolutely uniform in their powers, were diffused with absolute
uniformity through unlimited space, they would remain in equilibrium.
This however, though a verbally intelligible supposition, is one that
cannot be represented in thought; since unlimited space is
inconceivable. But all finite forms of the homogeneous�all forms of it
which we can know or conceive, must inevitably lapse into heterogeneity.
In three several ways does the persistence of force necessitate this.
Setting external agencies aside, each unit of a homogeneous whole must
be differently affected from any of the rest by the aggregate action of
the rest upon it. The resultant force exercised by the aggregate on each
unit, being in no two cases alike in both amount and direction, and
usually not in either, any incident force, even if uniform in amount and
direction, cannot produce like effects on the units. And the various
positions of the parts in relation to any incident force, preventing
them from receiving it in uniform amounts and directions, a further
difference in the effects wrought on them is inevitably produced.

One further remark is needed. To the conclusion that the changes with
which Evolution _commences_, are thus necessitated, remains to be added
the conclusion that these changes must _continue_. The absolutely
homogeneous must lose its equilibrium; and the relatively homogeneous
must lapse into the relatively less homogeneous. That which is true of
any total mass, is true of the parts into which it segregates. The
uniformity of each such part must as inevitably be lost in multiformity,
as was that of the original whole; and for like reasons. And thus the
continued changes which characterize Evolution, in so far as they are
constituted by the lapse of the homogeneous into the heterogeneous, and
of the less heterogeneous into the more heterogeneous, are necessary
consequences of the persistence of force.

-----

Footnote 16:

  The idea developed in this chapter originally formed part of an
  article on �Transcendental Physiology,� published in 1857. See
  _Essays_, pp. 279�290.




                              CHAPTER XIV.
                     THE MULTIPLICATION OF EFFECTS.


§ 116. To the cause of increasing complexity set forth in the last
chapter, we have in this chapter to add another. Though secondary in
order of time, it is scarcely secondary in order of importance. Even in
the absence of the cause already assigned, it would necessitate a change
from the homogeneous to the heterogeneous; and joined with it, it makes
this change both more rapid and more involved. To come in sight of it,
we have but to pursue a step further, that conflict between force and
matter already delineated. Let us do this.

When a uniform aggregate is subject to a uniform force, we have seen
that its constituents, being differently conditioned, are differently
modified. But while we have contemplated the various parts of the
aggregate as thus undergoing unlike changes, we have not yet
contemplated the unlike changes simultaneously produced on the various
parts of the incident force. These must be as numerous and important as
the others. Action and re-action being equal and opposite, it follows
that in differentiating the parts on which it falls in unlike ways, the
incident force must itself be correspondingly differentiated. Instead of
being as before, a uniform force, it must thereafter be a multiform
force�a group of dissimilar forces. A few illustrations will make this
truth manifest.

A single force is divided by conflict with matter into forces that
widely diverge. In the case lately cited, of a body shattered by violent
collision, besides the change of the homogeneous mass into a
heterogeneous group of scattered fragments, there is a change of the
homogeneous momentum into a group of momenta, heterogeneous in both
amounts and directions. Similarly with the forces we know as light and
heat. After the dispersion of these by a radiating body towards all
points, they are re-dispersed towards all points by the bodies on which
they fall. Of the Sun�s rays, issuing from him on every side, some few
strike the Moon. These being reflected at all angles from the Moon�s
surface, some few of them strike the Earth. By a like process the few
which reach the Earth are again diffused through surrounding space. And
on each occasion, such portions of the rays as are absorbed instead of
reflected, undergo refractions that equally destroy their parallelism.
      More than this is true. By conflict with matter, a uniform force
is in part changed into forces differing in their directions; and in
part it is changed into forces differing in their kinds. When one body
is struck against another, that which we usually regard as the effect,
is a change of position or motion in one or both bodies. But a moment�s
thought shows that this is a very incomplete view of the matter. Besides
the visible mechanical result, sound is produced; or, to speak
accurately, a vibration in one or both bodies, and in the surrounding
air: and under some circumstances we call this the effect. Moreover, the
air has not simply been made to vibrate, but has had currents raised in
it by the transit of the bodies. Further, if there is not that great
structural change which we call fracture, there is a disarrangement of
the particles of the two bodies around their point of collision;
amounting in some cases to a visible condensation. Yet more, this
condensation is accompanied by disengagement of heat. In some cases a
spark�that is, light�results, from the incandescence of a portion struck
off; and occasionally this incandescence is associated with chemical
combination. Thus, by the original mechanical force expended in the
collision, at least five, and often more, different kinds of forces have
been produced. Take, again, the lighting of a candle. Primarily, this is
a chemical change consequent on a rise of temperature. The process of
combination having once been set going by extraneous heat, there is a
continued formation of carbonic acid, water, &c.�in itself a result more
complex than the extraneous heat that first caused it. But along with
this process of combination there is a production of heat; there is a
production of light; there is an ascending column of hot gases
generated; there are currents established in the surrounding air. Nor
does the decomposition of one force into many forces end here. Each of
the several changes worked becomes the parent of further changes. The
carbonic acid formed, will by and by combine with some base; or under
the influence of sunshine give up its carbon to the leaf of a plant. The
water will modify the hygrometric state of the air around; or, if the
current of hot gases containing it come against a cold body, will be
condensed: altering the temperature, and perhaps the chemical state, of
the surface it covers. The heat given out melts the subjacent tallow,
and expands whatever it warms. The light, falling on various substances,
calls forth from them reactions by which it is modified; and so divers
colours are produced. Similarly even with these secondary actions, which
may be traced out into ever-multiplying ramifications, until they become
too minute to be appreciated.       Universally, then, the effect is
more complex than the cause. Whether the aggregate on which it falls be
homogeneous or otherwise, an incident force is transformed by the
conflict into a number of forces that differ in their amounts, or
directions, or kinds; or in all these respects. And of this group of
variously-modified forces, each ultimately undergoes a like
transformation.

Let us now mark how the process of evolution is furthered by this
multiplication of effects. An incident force decomposed by the reactions
of a body into a group of unlike forces�a uniform force thus reduced to
a multiform force�becomes the cause of a secondary increase of
multiformity in the body which decomposes it. In the last chapter we saw
that the several parts of an aggregate are differently modified by any
incident force. It has just been shown that by the reactions of the
differently modified parts, the incident force itself must be divided
into differently modified parts. Here it remains to point out that each
differentiated division of the aggregate, thus becomes a centre from
which a differentiated division of the original force is again diffused.
And since unlike forces must produce unlike results, each of these
differentiated forces must produce, throughout the aggregate, a further
series of differentiations.       This secondary cause of the change
from homogeneity to heterogeneity, obviously becomes more potent in
proportion as the heterogeneity increases. When the parts into which any
evolving whole has segregated itself, have diverged widely in nature,
they will necessarily react very diversely on any incident force�they
will divide an incident force into so many strongly contrasted groups of
forces. And each of them becoming the centre of a quite distinct set of
influences, must add to the number of distinct secondary changes wrought
throughout the aggregate.       Yet another corollary must be added. The
number of unlike parts of which an aggregate consists, as well as the
degree of their unlikeness, is an important factor in the process. Every
additional specialized division is an additional centre of specialized
forces. If a uniform whole, in being itself made multiform by an
incident force, makes the incident force multiform; if a whole
consisting of two unlike sections, divides an incident force into two
unlike groups of multiform forces; it is clear that each new unlike
section must be a further source of complication among the forces at
work throughout the mass�a further source of heterogeneity. The
multiplication of effects must proceed in geometrical progression. Each
stage of evolution must initiate a higher stage.

                  *       *       *       *       *

§ 117. The force of aggregation acting on irregular masses of rare
matter, diffused through a resisting medium, will not cause such masses
to move in straight lines to their common centre of gravity; but, as
before said, each will take a curvilinear path, directed to one or other
side of the centre of gravity. All of them being differently
conditioned, gravitation will impress on each a motion differing in
direction, in velocity, and in the degree of its curvature�uniform
aggregative force will be differentiated into multiform momenta. The
process thus commenced, must go on till it produces a single mass of
nebulous matter; and these independent curvilinear motions must result
in a movement of this mass round its axis: a simultaneous condensation
and rotation in which we see how two effects of the aggregative force,
at first but slightly divergent, become at last widely differentiated. A
gradual increase of oblateness in this revolving spheroid, must take
place through the joint action of these two forces, as the bulk
diminishes and the rotation grows more rapid; and this we may set down
as a third effect. The genesis of heat, which must accompany
augmentation of density, is a consequence of yet another order�a
consequence by no means simple; since the various parts of the mass,
being variously condensed, must be variously heated. Acting throughout a
gaseous spheroid, of which the parts are unlike in their temperatures,
the forces of aggregation and rotation must work a further series of
changes: they must set up circulating currents, both general and local.
At a later stage light as well as heat will be generated. Thus without
dwelling on the likelihood of chemical combinations and electric
disturbances, it is sufficiently manifest that, supposing matter to have
originally existed in a diffused state, the once uniform force which
caused its aggregation, must have become gradually divided into
different forces; and that each further stage of complication in the
resulting aggregate, must have initiated further subdivisions of this
force�a further multiplication of effects, increasing the previous
heterogeneity.

This section of the argument may however be adequately sustained,
without having recourse to any such hypothetical illustrations as the
foregoing. The astronomical attributes of the Earth, will even alone
suffice our purpose. Consider first the effects of its momentum round
its axis. There is the oblateness of its form; there is the alternation
of day and night; there are certain constant marine currents; and there
are certain constant aërial currents. Consider next the secondary series
of consequences due to the divergence of the Earth�s plane of rotation
from the plane of its orbit. The many differences of the seasons, both
simultaneous and successive, which pervade its surface, are thus caused.
External attraction acting on this rotating oblate spheroid with
inclined axis, produces the motion called nutation, and that slower and
larger one from which follows the precession of the equinoxes, with its
several sequences. And then by this same force are generated the tides,
aqueous and atmospheric.

Perhaps, however, the simplest way of showing the multiplication of
effects among phenomena of this order, will be to set down the
influences of any member of the Solar System on the rest. A planet
directly produces in neighbouring planets certain appreciable
perturbations, complicating those otherwise produced in them; and in the
remoter planets it directly produces certain less visible perturbations.
Here is a first series of effects. But each of the perturbed planets is
itself a source of perturbations�each directly affects all the others.
Hence, planet A having drawn planet B out of the position it would have
occupied in A�s absence, the perturbations which B causes are different
from what they would else have been; and similarly with C, D, E, &c.
Here then is a secondary series of effects: far more numerous though far
smaller in their amounts. As these indirect perturbations must to some
extent modify the movements of each planet, there results from them a
tertiary series; and so on continually. Thus the force exercised by any
planet works a different effect on each of the rest; this different
effect is from each as a centre partially broken up into minor different
effects on the rest; and so on in ever multiplying and diminishing waves
throughout the entire system.

                  *       *       *       *       *

§ 118. If the Earth was formed by the concentration of diffused matter,
it must at first have been incandescent; and whether the nebular
hypothesis be accepted or not, this original incandescence of the Earth
must now be regarded as inductively established�or, if not established,
at least rendered so probable that it is a generally admitted geological
doctrine. Several results of the gradual cooling of the Earth�as the
formation of a crust, the solidification of sublimed elements, the
precipitation of water, &c., have been already noticed�and I here again
refer to them merely to point out that they are simultaneous effects of
the one cause, diminishing heat. Let us now, however, observe the
multiplied changes afterwards arising from the continuance of this one
cause.       The Earth, falling in temperature, must contract. Hence the
solid crust at any time existing, is presently too large for the
shrinking nucleus; and being unable to support itself, inevitably
follows the nucleus. But a spheroidal envelope cannot sink down into
contact with a smaller internal spheroid, without disruption: it will
run into wrinkles, as the rind of an apple does when the bulk of its
interior decreases from evaporation. As the cooling progresses and the
envelope thickens, the ridges consequent on these contractions must
become greater; rising ultimately into hills and mountains; and the
later systems of mountains thus produced must not only be higher, as we
find them to be, but they must be longer, as we also find them to be.
Thus, leaving out of view other modifying forces, we see what immense
heterogeneity of surface arises from the one cause, loss of heat�a
heterogeneity which the telescope shows us to be paralleled on the Moon,
where aqueous and atmospheric agencies have been absent.       But we
have yet to notice another kind of heterogeneity of surface, similarly
and simultaneously caused. While the Earth�s crust was still thin, the
ridges produced by its contraction must not only have been small, but
the tracts between them must have rested with comparative smoothness on
the subjacent liquid spheroid; and the water in those arctic and
antarctic regions where it first condensed, must have been evenly
distributed. But as fast as the crust grew thicker and gained
corresponding strength, the lines of fracture from time to time caused
in it, necessarily occurred at greater distances apart; the intermediate
surfaces followed the contracting nucleus with less uniformity; and
there consequently resulted larger areas of land and water. If any one,
after wrapping an orange in wet tissue paper, and observing both how
small are the wrinkles and how evenly the intervening spaces lie on the
surface of the orange, will then wrap it in thick cartridge-paper, and
note both the greater height of the ridges and the larger spaces
throughout which the paper does not touch the orange, he will realize
the fact, that as the Earth�s solid envelope thickened, the areas of
elevation and depression became greater. In place of islands more or
less homogeneously scattered over an all-embracing sea, there must have
gradually arisen heterogeneous arrangements of continent and ocean, such
as we now know.       This double change in the extent and in the
elevation of the lands, involved yet another species of
heterogeneity�that of coast-line. A tolerably even surface raised out of
the ocean will have a simple, regular sea-margin; but a surface varied
by table-lands and intersected by mountain-chains, will, when raised out
of the ocean, have an outline extremely irregular, alike in its leading
features and in its details. Thus endless is the accumulation of
geological and geographical results slowly brought about by this one
cause�the escape of the Earth�s primitive heat.

When we pass from the agency which geologists term igneous, to aqueous
and atmospheric agencies, we see a like ever-growing complication of
effects. The denuding actions of air and water have, from the beginning,
been modifying every exposed surface: everywhere working many different
changes. As already shown (§ 80) the original source of those gaseous
and fluid motions which effect denudation, is the solar heat. The
transformation of this into various modes of force, according to the
nature and condition of the matter on which it falls, is the first stage
of complication. The sun�s rays, striking at all angles a sphere, that
from moment to moment presents and withdraws different parts of its
surface, and each of them for a different time daily throughout the
year, would produce a considerable variety of changes even were the
sphere uniform. But falling as they do on a sphere surrounded by an
atmosphere in some parts of which wide areas of cloud are suspended, and
which here unveils vast tracts of sea, there of level land, there of
mountains, there of snow and ice, they initiate in its several parts
countless different movements. Currents of air of all sizes, directions,
velocities, and temperatures, are set up; as are also marine currents
similarly contrasted in their characters. In this region the surface is
giving off water in the state of vapour; in that, dew is being
precipitated; and in the other rain is descending�differences that arise
from the ever-changing ratio between the absorption and radiation of
heat in each place. At one hour, a rapid fall in temperature leads to
the formation of ice, with an accompanying expansion throughout the
moist bodies frozen; while at another, a thaw unlocks the dislocated
fragments of these bodies. And then, passing to a second stage of
complication, we see that the many kinds of motion directly or
indirectly caused by the sun�s rays, severally produce results that vary
with the conditions. Oxidation, drought, wind, frost, rain, glaciers,
rivers, waves, and other denuding agents effect disintegrations that are
determined in their amounts and qualities by local circumstances. Acting
upon a tract of granite, such agents here work scarcely an appreciable
effect; there cause exfoliations of the surface, and a resulting heap of
_débris_ and boulders; and elsewhere, after decomposing the feldspar
into a white clay, carry away this with the accompanying quartz and
mica, and deposit them in separate beds, fluviatile and marine. When the
exposed land consists of several unlike formations, sedimentary and
igneous, changes proportionably more heterogeneous are wrought. The
formations being disintegrable in different degrees, there follows an
increased irregularity of surface. The areas drained by different rivers
being differently constituted, these rivers carry down to the sea unlike
combinations of ingredients; and so sundry new strata of distinct
composition arise. And here indeed we may see very simply illustrated,
the truth, that the heterogeneity of the effects increases in a
geometrical progression, with the heterogeneity of the object acted
upon. A continent of complex structure, presenting many strata
irregularly distributed, raised to various levels, tilted up at all
angles, must, under the same denuding agencies, give origin to immensely
multiplied results: each district must be peculiarly modified; each
river must carry down a distinct kind of detritus; each deposit must be
differently distributed by the entangled currents, tidal and other,
which wash the contorted shores; and every additional complication of
surface must be the cause of more than one additional consequence. But
not to dwell on these, let us, for the fuller elucidation of this truth
in relation to the inorganic world, consider what would presently follow
from some extensive cosmical revolution�say the subsidence of Central
America. The immediate results of the disturbance would themselves be
sufficiently complex. Besides the numberless dislocations of strata, the
ejections of igneous matter, the propagation of earthquake vibrations
thousands of miles around, the loud explosions, and the escape of gases,
there would be the rush of the Atlantic and Pacific Oceans to supply the
vacant space, the subsequent recoil of enormous waves, which would
traverse both these oceans and produce myriads of changes along their
shores, the corresponding atmospheric waves complicated by the currents
surrounding each volcanic vent, and the electrical discharges with which
such disturbances are accompanied. But these temporary effects would be
insignificant compared with the permanent ones. The complex currents of
the Atlantic and Pacific would be altered in directions and amounts. The
distribution of heat achieved by these currents would be different from
what it is. The arrangement of the isothermal lines, not only on the
neighbouring continents, but even throughout Europe, would be changed.
The tides would flow differently from what they do now. There would be
more or less modification of the winds in their periods, strengths,
directions, qualities. Rain would fall scarcely anywhere at the same
times and in the same quantities as at present. In short, the
meteorological conditions thousands of miles off, on all sides, would be
more or less revolutionized. In these many changes, each of which
comprehends countless minor ones, the reader will see the immense
heterogeneity of the results wrought out by one force, when that force
expends itself on a previously complicated area; and he will readily
draw the corollary that from the beginning the complication has advanced
at an increasing rate.

                  *       *       *       *       *

§ 119. We have next to trace throughout organic evolution, this same
all-pervading principle. And here, where the transformation of the
homogeneous into the heterogeneous was first observed, the production of
many changes by one cause is least easy to demonstrate. The development
of a seed into a plant, or an ovum into an animal, is so gradual; while
the forces which determine it are so involved, and at the same time so
unobtrusive; that it is difficult to detect the multiplication of
effects which is elsewhere so obvious. Nevertheless, by indirect
evidence we may establish our proposition; spite of the lack of direct
evidence.

Observe, first, how numerous are the changes which any marked stimulus
works on an adult organism�a human being, for instance. An alarming
sound or sight, besides impressions on the organs of sense and the
nerves, may produce a start, a scream, a distortion of the face, a
trembling consequent on general muscular relaxation, a burst of
perspiration, an excited action of the heart, a rush of blood to the
brain, followed possibly by arrest of the heart�s action and by syncope;
and if the system be feeble, an illness with its long train of
complicated symptoms may set in. Similarly in cases of disease. A minute
portion of the small-pox virus introduced into the system, will, in a
severe case, cause, during the first stage, rigors, heat of skin,
accelerated pulse, furred tongue, loss of appetite, thirst, epigastric
uneasiness, vomiting, headache, pains in the back and limbs, muscular
weakness, convulsions, delirium, &c.; in the second stage, cutaneous
eruption, itching, tingling, sore throat, swelled fauces, salivation,
cough, hoarseness, dyspn�a, &c.; and in the third stage, �dematous
inflammations, pneumonia, pleurisy, diarrh�a, inflammation of the brain,
ophthalmia, erysipelas, &c.: each of which enumerated symptoms is itself
more or less complex. Medicines, special foods, better air, might in
like manner be instanced as producing multiplied results.       Now it
needs only to consider that the many changes thus wrought by one force
on an adult organism, must be partially paralleled in an
embryo-organism, to understand how here also the production of many
effects by one cause is a source of increasing heterogeneity. The
external heat and other agencies which determine the first complications
of the germ, will, by acting on these, superinduce further
complications; on these still higher and more numerous ones; and so on
continually: each organ as it is developed, serving, by its actions and
reactions on the rest, to initiate new complexities. The first
pulsations of the f�tal heart must simultaneously aid the unfolding of
every part. The growth of each tissue, by taking from the blood special
proportions of elements, must modify the constitution of the blood; and
so must modify the nutrition of all the other tissues. The distributive
actions, implying as they do a certain waste, necessitate an addition to
the blood of effete matters, which must influence the rest of the
system, and perhaps, as some think, initiate the formation of excretory
organs. The nervous connections established among the viscera must
further multiply their mutual influences. And so with every modification
of structure�every additional part and every alteration in the ratios of
parts.       Still stronger becomes the proof when we call to mind the
fact, that the same germ may be evolved into different forms according
to circumstances. Thus, during its earlier stages, every embryo is
sexless�becomes either male or female as the balance of forces acting on
it determines. Again, it is well-known that the larva of a working-bee
will develop into a queen-bee, if, before a certain period, its food be
changed to that on which the larvæ of queen-bees are fed. Even more
remarkable is the case of certain entozoa. The ovum of a tape-worm,
getting into the intestine of one animal, unfolds into the form of its
parent; but if carried into other parts of the system, or into the
intestine of some unlike animal, it becomes one of the sac-like
creatures, called by naturalists _Cysticerci_, or _C�nuri_, or
_Echinococci_�creatures so extremely different from the tape-worm in
aspect and structure, that only after careful investigations have they
been proved to have the same origin. All which instances imply that each
advance in embryonic complication results from the action of incident
forces on the complication previously existing.       Indeed, the now
accepted doctrine of epigenesis necessitates the conclusion that organic
evolution proceeds after this manner. For since it is proved that no
germ, animal or vegetal, contains the slightest rudiment, trace, or
indication of the future organism�since the microscope has shown us that
the first process set up in every fertilized germ is a process of
repeated spontaneous fissions, ending in the production of a mass of
cells, not one of which exhibits any special character; there seems no
alternative but to conclude that the partial organization at any moment
subsisting in a growing embryo, is transformed by the agencies acting on
it into the succeeding phase of organization, and this into the next,
until, through ever-increasing complexities, the ultimate form is
reached.       Thus, though the subtlety of the forces and the slowness
of the metamorphosis, prevent us from _directly_ tracing the genesis of
many changes by one cause, throughout the successive stages which every
embryo passes through; yet, _indirectly_, we have strong evidence that
this is a source of increasing heterogeneity. We have marked how
multitudinous are the effects which a single agency may generate in an
adult organism; that a like multiplication of effects must happen in the
unfolding organism, we have inferred from sundry illustrative cases;
further, it has been pointed out that the ability which like germs have
to originate unlike forms, implies that the successive transformations
result from the new changes superinduced on previous changes; and we
have seen that structureless as every germ originally is, the
development of an organism out of it is otherwise incomprehensible.
Doubtless we are still in the dark respecting those mysterious
properties which make the germ, when subject to fit influences, undergo
the special changes beginning this series of transformations. All here
contended is, that given a germ possessing these mysterious properties,
the evolution of an organism from it depends, in part, on that
multiplication of effects which we have seen to be a cause of evolution
in general, so far as we have yet traced it.

When, leaving the development of single plants and animals, we pass to
that of the Earth�s flora and fauna, the course of the argument again
becomes clear and simple. Though, as before admitted, the fragmentary
facts Palæontology has accumulated, do not clearly warrant us in saying
that, in the lapse of geologic time, there have been evolved more
heterogeneous organisms, and more heterogeneous assemblages of
organisms; yet we shall now see that there _must_ ever have been a
tendency towards these results. We shall find that the production of
many effects by one cause, which, as already shown, has been all along
increasing the physical heterogeneity of the Earth, has further
necessitated an increasing heterogeneity in its flora and fauna,
individually and collectively. An illustration will make this clear.
      Suppose that by a series of upheavals, occurring, as they are now
known to do, at long intervals, the East Indian Archipelago were to be
raised into a continent, and a chain of mountains formed along the axis
of elevation. By the first of these upheavals, the plants and animals
inhabiting Borneo, Sumatra, New Guinea, and the rest, would be subjected
to slightly-modified sets of conditions. The climate in general would be
altered in temperature, in humidity, and in its periodical variations;
while the local differences would be multiplied. These modifications
would affect, perhaps inappreciably, the entire flora and fauna of the
region. The change of level would produce additional modifications;
varying in different species, and also in different members of the same
species, according to their distance from the axis of elevation. Plants,
growing only on the sea-shore in special localities, might become
extinct. Others, living only in swamps of a certain humidity, would, if
they survived at all, probably undergo visible changes of appearance.
While more marked alterations would occur in some of the plants that
spread over the lands newly raised above the sea. The animals and
insects living on these modified plants, would themselves be in some
degree modified by change of food, as well as by change of climate; and
the modification would be more marked where, from the dwindling or
disappearance of one kind of plant, an allied kind was eaten. In the
lapse of the many generations arising before the next upheaval, the
sensible or insensible alterations thus produced in each species, would
become organized�in all the races that survived there would be a more or
less complete adaptation to the new conditions. The next upheaval would
superinduce further organic changes, implying wider divergences from the
primary forms; and so repeatedly. Now however let it be observed that
this revolution would not be a substitution of a thousand modified
species for the thousand original species; but in place of the thousand
original species there would arise several thousand species, or
varieties, or changed forms. Each species being distributed over an area
of some extent, and tending continually to colonize the new area
exposed, its different members would be subject to different sets of
changes. Plants and animals migrating towards the equator would not be
affected in the same way with others migrating from it. Those which
spread towards the new shores, would undergo changes unlike the changes
undergone by those which spread into the mountains. Thus, each original
race of organisms would become the root from which diverged several
races, differing more or less from it and from each other; and while
some of these might subsequently disappear, probably more than one would
survive in the next geologic period: the very dispersion itself
increasing the chances of survival. Not only would there be certain
modifications thus caused by changes of physical conditions and food;
but also in some cases other modifications caused by changes of habit.
The fauna of each island, peopling, step by step, the newly-raised
tracts, would eventually come in contact with the faunas of other
islands; and some members of these other faunas would be unlike any
creatures before seen. Herbivores meeting with new beasts of prey,
would, in some cases, be led into modes of defence or escape differing
from those previously used; and simultaneously the beasts of prey would
modify their modes of pursuit and attack. We know that when
circumstances demand it, such changes of habit _do_ take place in
animals; and we know that if the new habits become the dominant ones,
they must eventually in some degree alter the organization.
      Observe now, however, a further consequence. There must arise not
simply a tendency towards the differentiation of each race of organisms
into several races; but also a tendency to the occasional production of
a somewhat higher organism. Taken in the mass, these divergent
varieties, which have been caused by fresh physical conditions and
habits of life, will exhibit alterations quite indefinite in kind and
degree; and alterations that do not necessarily constitute an advance.
Probably in most cases the modified type will be not appreciably more
heterogeneous than the original one. But it _must_ now and then occur,
that some division of a species, falling into circumstances which give
it rather more complex experiences, and demand actions somewhat more
involved, will have certain of its organs further differentiated in
proportionately small degrees�will become slightly more heterogeneous.
Hence, there will from time to time arise an increased heterogeneity
both of the Earth�s flora and fauna, and of individual races included in
them. Omitting detailed explanations, and allowing for the
qualifications which cannot here be specified, it is sufficiently clear
that geological mutations have all along tended to complicate the forms
of life, whether regarded separately or collectively. That
multiplication of effects which has been a part-cause of the
transformation of the Earth�s crust from the simple into the complex,
has simultaneously led to a parallel transformation of the Life upon its
surface.[17]

The deduction here drawn from the established truths of geology and the
general laws of life, gains immensely in weight on finding it to be in
harmony with an induction drawn from direct experience. Just that
divergence of many races from one race, which we inferred must have been
continually occurring during geologic time, we know to have occurred
during the pre-historic and historic periods, in man and domestic
animals. And just that multiplication of effects which we concluded must
have been instrumental to the first, we see has in a great measure
wrought the last. Single causes, as famine, pressure of population, war,
have periodically led to further dispersions of mankind and of dependent
creatures: each such dispersion initiating new modifications, new
varieties of type. Whether all the human races be or be not derived from
one stock, philology makes it clear that whole groups of races, now
easily distinguishable from each other, were originally one race�that
the diffusion of one race into different climates and conditions of
existence has produced many altered forms of it. Similarly with domestic
animals. Though in some cases (as that of dogs) community of origin will
perhaps be disputed, yet in other cases (as that of the sheep or the
cattle of our own country) it will not be questioned that local
differences of climate, food, and treatment, have transformed one
original breed into numerous breeds, now become so far distinct as to
produce unstable hybrids. Moreover, through the complication of effects
flowing from single causes, we here find, what we before inferred, not
only an increase of general heterogeneity, but also of special
heterogeneity. While of the divergent divisions and subdivisions of the
human race, many have undergone changes not constituting an advance;
others have become decidedly more heterogeneous. The civilized European
departs more widely from the vertebrate archetype than does the savage.

                  *       *       *       *       *

§ 120. A sensation does not expend itself in arousing some single state
of consciousness; but the state of consciousness aroused is made up of
various represented sensations connected by co-existence, or sequence
with the presented sensation. And that, in proportion as the grade of
intelligence is high, the number of ideas suggested is great, may be
readily inferred. Let us, however, look at the proof that here too, each
change is the parent of many changes; and that the multiplication
increases in proportion as the area affected is complex.

Were some hitherto unknown bird, driven say by stress of weather from
the remote north, to make its appearance on our shores, it would excite
no speculation in the sheep or cattle amid which it alighted: a
perception of it as a creature like those constantly flying about, would
be the sole interruption of that dull current of consciousness which
accompanies grazing and rumination. The cow-herd, by whom we may suppose
the exhausted bird to be presently caught, would probably gaze at it
with some slight curiosity, as being unlike any he had before seen�would
note its most conspicuous markings, and vaguely ponder on the questions,
where it came from, and how it came. The village bird-stuffer would have
suggested to him by the sight of it, sundry forms to which it bore a
little resemblance; would receive from it more numerous and more
specific impressions respecting structure and plumage; would be reminded
of various instances of birds brought by storms from foreign parts�would
tell who found them, who stuffed them, who bought them. Supposing the
unknown bird taken to a naturalist of the old school, interested only in
externals, (one of those described by the late Edward Forbes, as
examining animals as though they were merely skins filled with straw,)
it would excite in him a more involved series of mental changes: there
would be an elaborate examination of the feathers, a noting of all their
technical distinctions, with a reduction of these perceptions to certain
equivalent written symbols; reasons for referring the new form to a
particular family, order, and genus would be sought out and written
down; communications with the secretary of some society, or editor of
some journal, would follow; and probably there would be not a few
thoughts about the addition of the _ii_ to the describer�s name, to form
the name of the species. Lastly, in the mind of a comparative anatomist,
such a new species, should it happen to have any marked internal
peculiarity, might produce additional sets of changes�might very
possibly suggest modified views respecting the relationships of the
division to which it belonged; or, perhaps, alter his conceptions of the
homologies and developments of certain organs; and the conclusions drawn
might not improbably enter as elements into still wider inquiries
concerning the origin of organic forms.

From ideas let us turn to emotions. In a young child, a father�s anger
produces little else than vague fear�a disagreeable sense of impending
evil, taking various shapes of physical suffering or deprivation of
pleasures. In elder children, the same harsh words will arouse
additional feelings: sometimes a sense of shame, of penitence, or of
sorrow for having offended; at other times, a sense of injustice, and a
consequent anger. In the wife, yet a further range of feelings may come
into existence�perhaps wounded affection, perhaps self-pity for
ill-usage, perhaps contempt for groundless irritability, perhaps
sympathy for some suffering which the irritability indicates, perhaps
anxiety about an unknown misfortune which she thinks has produced it.
Nor are we without evidence that among adults, the like differences of
development are accompanied by like differences in the number of
emotions that are aroused, in combination or rapid succession�the lower
natures being characterized by that impulsiveness which results from the
uncontrolled action of a few feelings; and the higher natures being
characterized by the simultaneous action of many secondary feelings,
modifying those first awakened.

Possibly it will be objected that the illustrations here given, are
drawn from the functional changes of the nervous system, not from its
structural changes; and that what is proved among the first, does not
necessarily hold among the last. This must be admitted. Those, however,
who recognize the truth that the structural changes are the slowly
accumulated results of the functional changes, will readily draw the
corollary, that a part-cause of the evolution of the nervous system, as
of other evolution, is this multiplication of effects which becomes ever
greater as the development becomes higher.

                  *       *       *       *       *

§ 121. If the advance of Man towards greater heterogeneity in both body
and mind, is in part traceable to the production of many effects by one
cause, still more clearly may the advance of Society towards greater
heterogeneity be so explained. Consider the growth of an industrial
organization. When, as must occasionally happen, some individual of a
tribe displays unusual aptitude for making an article of general use (a
weapon, for instance) which was before made by each man for himself,
there arises a tendency towards the differentiation of that individual
into a maker of weapons. His companions (warriors and hunters all of
them) severally wish to have the best weapons that can be made; and are
therefore certain to offer strong inducements to this skilled individual
to make weapons for them. He, on the other hand, having both an unusual
faculty, and an unusual liking, for making weapons (the capacity and the
desire for any occupation being commonly associated), is predisposed to
fulfil these commissions on the offer of adequate rewards: especially as
his love of distinction is also gratified. This first specialization of
function, once commenced, tends ever to become more decided. On the side
of the weapon-maker, continued practice gives increased skill�increased
superiority to his products. On the side of his clients, cessation of
practice entails decreased skill. Thus the influences that determine
this division of labour grow stronger in both ways: this social movement
tends ever to become more decided in the direction in which it was first
set up; and the incipient heterogeneity is, on the average of cases,
likely to become permanent for that generation, if no longer.       Such
a process, besides differentiating the social mass into two parts, the
one monopolizing, or almost monopolizing, the performance of a certain
function, and the other having lost the habit, and in some measure the
power, of performing that function, has a tendency to initiate other
differentiations. The advance described implies the introduction of
barter: the maker of weapons has, on each occasion, to be paid in such
other articles as he agrees to take in exchange. Now he will not
habitually take in exchange one kind of article, but many kinds. He does
not want mats only, or skins, or fishing-gear; but he wants all these;
and on each occasion will bargain for the particular things he most
needs. What follows? If among the members of the tribe there exist any
slight differences of skill in the manufacture of these various things,
as there are almost sure to do, the weapon-maker will take from each one
the thing which that one excels in making: he will exchange for mats
with him whose mats are superior, and will bargain for the fishing-gear
of whoever has the best. But he who has bartered away his mats or his
fishing-gear, must make other mats or fishing-gear for himself; and in
so doing must, in some degree, further develop his aptitude. Thus it
results that the small specialities of faculty possessed by various
members of the tribe will tend to grow more decided. If such
transactions are from time to time repeated, these specializations may
become appreciable. And whether or not there ensue distinct
differentiations of other individuals into makers of particular
articles, it is clear that incipient differentiations take place
throughout the tribe: the one original cause produces not only the first
dual effect, but a number of secondary dual effects, like in kind but
minor in degree.       This process, of which traces may be seen among
groups of school-boys, cannot well produce a lasting distribution of
functions in an unsettled tribe; but where there grows up a fixed and
multiplying community, such differentiations become permanent, and
increase with each generation. An addition to the number of citizens,
involving a greater demand for every commodity, intensifies the
functional activity of each specialized person or class; and this
renders the specialization more definite where it already exists, and
establishes it where it is but nascent. By increasing the pressure on
the means of subsistence, a larger population again augments these
results; since every individual is forced more and more to confine
himself to that which he can do best, and by which he can gain most. And
this industrial progress, by aiding future production, opens the way for
further growth of population, which reacts as before.       Presently,
under the same stimuli, new occupations arise. Competing workers,
severally aiming to produce improved articles, occasionally discover
better processes or better materials. In weapons and cutting-tools, the
substitution of bronze for stone entails on him who first makes it, a
great increase of demand�so great an increase that he presently finds
all his time occupied in making the bronze for the articles he sells,
and is obliged to depute the fashioning of these articles to others; and
eventually the making of bronze, thus gradually differentiated from a
pre-existing occupation, becomes an occupation by itself. But now mark
the ramified changes which follow this change. Bronze soon replaces
stone, not only in the articles it was first used for, but in many
others; and so affects the manufacture of them. Further, it affects the
processes which such improved utensils subserve, and the resulting
products�modifies buildings, carvings, dress, personal decorations. Yet
again, it sets going sundry manufactures which were before impossible,
from lack of a material fit for the requisite tools. And all these
changes react on the people�increase their manipulative skill, their
intelligence, their comfort�refine their habits and tastes.

It is out of the question here to follow through its successive
complications, this increasing social heterogeneity that results from
the production of many effects by one cause. But leaving the
intermediate phases of social development, let us take an illustration
from its passing phase. To trace the effects of steam-power, in its
manifold applications to mining, navigation, and manufactures, would
carry us into unmanageable detail. Let us confine ourselves to the
latest embodiment of steam-power�the locomotive engine. This, as the
proximate cause of our railway-system, has changed the face of the
country, the course of trade, and the habits of the people. Consider,
first, the complicated sets of changes that precede the making of every
railway�the provisional arrangements, the meetings, the registration,
the trial-section, the parliamentary survey, the lithographed plans, the
books of reference, the local deposits and notices, the application to
Parliament, the passing Standing-Orders Committee, the first, second,
and third readings: each of which brief heads indicates a multiplicity
of transactions, and the further development of sundry occupations, (as
those of engineers, surveyors, lithographers, parliamentary agents,
share-brokers,) and the creation of sundry others (as those of
traffic-takers, reference-takers). Consider, next, the yet more marked
changes implied in railway construction�the cuttings, em-bankings,
tunnellings, diversions of roads; the building of bridges and stations;
the laying down of ballast, sleepers, and rails; the making of engines,
tenders, carriages, and wagons: which processes, acting upon numerous
trades, increase the importation of timber, the quarrying of stone, the
manufacture of iron, the mining of coal, the burning of bricks;
institute a variety of special manufactures weekly advertised in the
_Railway Times_; and call into being some new classes of
workers�drivers, stokers, cleaners, plate-layers, &c. &c. Then come the
changes, more numerous and involved still, which railways in action
produce on the community at large. The organization of every business is
more or less modified: ease of communication makes it better to do
directly what was before done by proxy; agencies are established where
previously they would not have paid; goods are obtained from remote
wholesale houses instead of near retail ones; and commodities are used
which distance once rendered inaccessible. The rapidity and small cost
of carriage, tend to specialize more than ever the industries of
different districts�to confine each manufacture to the parts in which,
from local advantages, it can be best carried on. Economical
distribution equalizes prices, and also, on the average, lowers prices:
thus bringing divers articles within the means of those before unable to
buy them, and so increasing their comforts and improving their habits.
At the same time the practice of travelling is immensely extended.
Classes who before could not afford it, take annual trips to the sea;
visit their distant relations; make tours; and so we are benefited in
body, feelings, and intellect. The more prompt transmission of letters
and of news produces further changes�makes the pulse of the nation
faster. Yet more, there arises a wide dissemination of cheap literature
through railway book-stalls, and of advertisements in railway carriages:
both of them aiding ulterior progress. And the innumerable changes here
briefly indicated are consequent on the invention of the locomotive
engine. The social organism has been rendered more heterogeneous, in
virtue of the many new occupations introduced, and the many old ones
further specialized; prices in all places have been altered; each trader
has, more or less, modified his way of doing business; and every person
has been affected in his actions, thoughts, emotions.

The only further fact demanding notice, is, that we here see more
clearly than ever, that in proportion as the area over which any
influence extends, becomes heterogeneous, the results are in a yet
higher degree multiplied in number and kind. While among the primitive
tribes to whom it was first known, caoutchouc caused but few changes,
among ourselves the changes have been so many and varied that the
history of them occupies a volume. Upon the small, homogeneous community
inhabiting one of the Hebrides, the electric telegraph would produce,
were it used, scarcely any results; but in England the results it
produces are multitudinous.

Space permitting, the synthesis might here be pursued in relation to all
the subtler products of social life. It might be shown how, in Science,
an advance of one division presently advances other divisions�how
Astronomy has been immensely forwarded by discoveries in Optics, while
other optical discoveries have initiated Microscopic Anatomy, and
greatly aided the growth of Physiology�how Chemistry has indirectly
increased our knowledge of Electricity, Magnetism, Biology, Geology�how
Electricity has reacted on Chemistry and Magnetism, developed our views
of Light and Heat, and disclosed sundry laws of nervous action. In
Literature the same truth might be exhibited in the still-multiplying
forms of periodical publications that have descended from the first
newspaper, and which have severally acted and reacted on other forms of
literature and on each other; or in the bias given by each book of power
to various subsequent books. The influence which a new school of
Painting (as that of the pre-Raphaelites) exercises on other schools;
the hints which all kinds of pictorial art are deriving from
Photography; the complex results of new critical doctrines; might
severally be dwelt on as displaying the like multiplication of effects.
But it would needlessly tax the reader�s patience to detail, in their
many ramifications, these various changes: here become so involved and
subtle as to be followed with some difficulty.

                  *       *       *       *       *

§ 122. After the argument which closed the last chapter, a parallel one
seems here scarcely required. For symmetry�s sake, however, it will be
proper briefly to point out how the multiplication of effects, like the
instability of the homogeneous, is a corollary from the persistence of
force.

Things which we call different are things which react in different ways;
and we can know them as different only by the differences in their
reactions. When we distinguish bodies as hard and soft, rough and
smooth, we simply mean that certain like muscular forces expended on
them are followed by unlike sets of sensations�unlike re-active forces.
Objects that are classed as red, blue, yellow, &c., are objects that
decompose light in strongly-contrasted ways; that is, we know contrasts
of colour as contrasts in the changes produced in a uniform incident
force. Manifestly, any two things which do not work unequal effects on
consciousness, either by unequally opposing our own energies, or by
impressing our senses with unequally modified forms of certain external
energies, cannot be distinguished by us. Hence the proposition that the
different parts of any whole must react differently on a uniform
incident force, and must so reduce it to a group of multiform forces, is
in essence a truism. A further step will reduce this truism to its
lowest terms.

When, from unlikeness between the effects they produce on consciousness,
we predicate unlikeness between two objects, what is our warrant? and
what do we mean by the unlikeness, objectively considered? Our warrant
is the persistence of force. Some kind or amount of change has been
wrought in us by the one, which has not been wrought by the other. This
change we ascribe to some force exercised by the one which the other has
not exercised. And we have no alternative but to do this, or to assert
that the change had no antecedent; which is to deny the persistence of
force. Whence it is further manifest that what we regard as the
objective unlikeness is the presence in the one of some force, or set of
forces, not present in the other�something in the kinds or amounts or
directions of the constituent forces of the one, which those of the
other do not parallel. But now if things or parts of things which we
call different, are those of which the constituent forces differ in one
or more respects; what must happen to any like forces, or any uniform
force, falling on them? Such like forces, or parts of a uniform force,
must be differently modified. The force which is present in the one and
not in the other, must be an element in the conflict�must produce its
equivalent reaction; and must so affect the total reaction. To say
otherwise is to say that this differential force will produce no effect;
which is to say that force is not persistent.

I need not develop this corollary further. It manifestly follows that a
uniform force, falling on a uniform aggregate, must undergo dispersion;
that falling on an aggregate made up of unlike parts, it must undergo
dispersion from each part, as well as qualitative differentiations; that
in proportion as the parts are unlike, these qualitative
differentiations must be marked; that in proportion to the number of the
parts, they must be numerous; that the secondary forces so produced,
must undergo further transformations while working equivalent
transformations in the parts that change them; and similarly with the
forces they generate. Thus the conclusions that a part-cause of
Evolution is the multiplication of effects; and that this increases in
geometrical progression as the heterogeneity becomes greater; are not
only to be established inductively, but are deducible from the deepest
of all truths.

-----

Footnote 17:

  Had this paragraph, first published in the _Westminster Review_ in
  1857, been written after the appearance of Mr. Darwin�s work on _The
  Origin of Species_, it would doubtless have been otherwise expressed.
  Reference would have been made to the process of �natural selection,�
  as greatly facilitating the differentiations described. As it is,
  however, I prefer to let the passage stand in its original shape:
  partly because it seems to me that these successive changes of
  conditions would produce divergent varieties or species, apart from
  the influence of �natural selection� (though in less numerous ways as
  well as less rapidly); and partly because I conceive that in the
  absence of these successive changes of conditions, �natural selection�
  would effect comparatively little. Let me add that though these
  positions are not enunciated in _The Origin of Species_, yet a mutual
  friend gives me reason to think that Mr. Darwin would coincide in
  them; if he did not indeed consider them as tacitly implied in his
  work.




                              CHAPTER XV.
                    DIFFERENTIATION AND INTEGRATION.


§ 123. The general interpretation of Evolution is far from being
completed in the preceding chapters. We must contemplate its changes
under yet another aspect, before we can form a definite conception of
the process constituted by them. Though the laws already set forth,
furnish a key to the re-arrangement of parts which Evolution exhibits,
in so far as it is an advance from the uniform to the multiform; they
furnish no key to this re-arrangement in so far as it is an advance from
the indefinite to the definite. On studying the actions and re-actions
everywhere going on, we have found it to follow inevitably from a
certain primordial truth, that the homogeneous must lapse into the
heterogeneous, and that the heterogeneous must become more
heterogeneous; but we have not discovered why the differently-affected
parts of any simple whole, become clearly marked off from each other, at
the same time that they become unlike. Thus far no reason has been
assigned why there should not ordinarily arise a vague chaotic
heterogeneity, in place of that orderly heterogeneity displayed in
Evolution. It still remains to find out the cause of that integration of
parts which accompanies their differentiation�that gradually-completed
segregation of like units into a group, distinctly separated from
neighbouring groups which are severally made up of other kinds of units.
The rationale will be conveniently introduced by a few instances in
which we may watch this segregative process taking place.

When towards the end of September, the trees are gaining their autumn
colours, and we are hoping shortly to see a further change increasing
still more the beauty of the landscape, we are not uncommonly
disappointed by the occurrence of an equinoxial gale. Out of the mixed
mass of foliage on each branch, the strong current of air carries away
the decaying and brightly-tinted leaves, but fails to detach those which
are still green. And while these last, frayed and seared by
long-continued beatings against each other, and the twigs around them,
give a sombre colour to the woods, the red and yellow and orange leaves
are collected together in ditches and behind walls and in corners where
eddies allow them to settle. That is to say, by the action of that
uniform force which the wind exerts on both kinds, the dying leaves are
picked out from among their still living companions and gathered in
places by themselves. Again, the separation of particles of different
sizes, as dust and sand from pebbles, may be similarly effected; as we
see on every road in March. And from the days of Homer downwards, the
power of currents of air, natural and artificial, to part from one
another units of unlike specific gravities, has been habitually utilized
in the winnowing of chaff from wheat.       In every river we see how
the mixed materials carried down, are separately deposited�how in rapids
the bottom gives rest to nothing but boulders and pebbles; how where the
current is not so strong, sand is let fall; and how, in still places,
there is a sediment of mud. This selective action of moving water, is
commonly applied in the arts to obtain masses of particles of different
degrees of fineness. Emery, for example, after being ground, is carried
by a slow current through successive compartments; in the first of which
the largest grains subside; in the second of which the grains that reach
the bottom before the water has escaped, are somewhat smaller; in the
third smaller still; until in the last there are deposited only those
finest particles which fall so slowly through the water, that they have
not previously been able to reach the bottom. And in a way that is
different though equally significant, this segregative effect of water
in motion, is exemplified in the carrying away of soluble from insoluble
matters�an application of it hourly made in every laboratory.       The
effects of the uniform forces which aerial and aqueous currents
exercise, are paralleled by those of uniform forces of other orders.
Electric attraction will separate small bodies from large, or light
bodies from heavy. By magnetism, grains of iron may be selected from
among other grains; as by the Sheffield grinder, whose magnetized gauze
mask filters out the steel-dust which his wheel gives off, from the
stone-dust that accompanies it. And how the affinity of any agent acting
differently on the components of a given body, enables us to take away
some component and leave the rest behind, is shown in almost every
chemical experiment.

What now is the general truth here variously presented? How are these
several facts and countless similar ones, to be expressed in terms that
embrace them all? In each case we see in action a force which may be
regarded as simple or uniform�fluid motion in a certain direction at a
certain velocity; electric or magnetic attraction of a given amount;
chemical affinity of a particular kind: or rather, in strictness, the
acting force is compounded of one of these and certain other uniform
forces, as gravitation, etc. In each case we have an aggregate made up
of unlike units�either atoms of different substances combined or
intimately mingled, or fragments of the same substance of different
sizes, or other constituent parts that are unlike in their specific
gravities, shapes, or other attributes. And in each case these unlike
units, or groups of units, of which the aggregate consists, are, under
the influence of some resultant force acting indiscriminately on them
all, separated from each other�segregated into minor aggregates, each
consisting of units that are severally like each other and unlike those
of the other minor aggregates. Such being the common aspect of these
changes, let us look for the common interpretation of them.

In the chapter on �The Instability of the Homogeneous,� it was shown
that a uniform force falling on any aggregate, produces unlike
modifications in its different parts�turns the uniform into the
multiform and the multiform into the more multiform. The transformation
thus wrought, consists of either insensible or sensible changes of
relative position among the units, or of both�either of those molecular
re-arrangements which we call chemical, or of those larger
transpositions which are distinguished as mechanical, or of the two
united. Such portion of the permanently effective force as reaches each
different part, or differently-conditioned part, may be expended in
modifying the mutual relations of its constituents; or it may be
expended in moving the part to another place; or it may be expended
partially in the first and partially in the second. Hence, so much of
the permanently effective force as does not work the one kind of effect,
must work the other kind. It is manifest that if of the permanently
effective force which falls on some compound unit of an aggregate,
little, if any, is absorbed in re-arranging the ultimate components of
such compound unit, much or the whole, must show itself in motion of
such compound unit to some other place in the aggregate; and conversely,
if little or none of this force is absorbed in generating mechanical
transposition, much or the whole must go to produce molecular
alterations.       What now must follow from this? In cases where none
or only part of the force generates chemical re-distributions, what
physical re-distributions must be generated? Parts that are similar to
each other will be similarly acted on by the force; and will similarly
react on it. Parts that are dissimilar will be dissimilarly acted on by
the force; and will dissimilarly react on it. Hence the permanently
effective incident force, when wholly or partially transformed into
mechanical motion of the units, will produce like motions in units that
are alike, and unlike motions in units that are unlike. If then, in an
aggregate containing two or more orders of mixed units, those of the
same order will be moved in the same way, and in a way that differs from
that in which units of other orders are moved, the respective orders
must segregate. A group of like things on which are impressed motions
that are alike in amount and direction, must be transferred as a group
to another place, and if they are mingled with some group of other
things, on which the motions impressed are like each other, but unlike
those of the first group in amount or direction or both, these other
things must be transferred as a group to some other place�the mixed
aggregate must undergo a simultaneous differentiation and integration.

In further elucidation of this process, it will be well here to set down
a few instances in which we may see that, other things equal, the
definiteness of the separation is in proportion to the definiteness of
the difference between the units. Take a handful of any pounded
substance, containing fragments of all sizes; and let it fall to the
ground while a gentle breeze is blowing. The large fragments will be
collected together on the ground almost immediately under the hand;
somewhat smaller fragments will be carried a little to the leeward;
still smaller ones a little further; and those minute particles which we
call dust, will be drifted a long way before they reach the earth: that
is, the integration is indefinite where the difference among the
fragments is indefinite, though the divergence is greatest where the
difference is greatest. If, again, the handful be made up of quite
distinct orders of units�as pebbles, coarse sand, and dust�these will,
under like conditions, be segregated with comparative definiteness: the
pebbles will drop almost vertically; the sand will fall in an inclined
direction, and deposit itself within a tolerably circumscribed space
beyond the pebbles; while the dust will be blown almost horizontally to
a great distance. A case in which another kind of force comes into play,
will still better illustrate this truth. Through a mixed aggregate of
soluble and insoluble substances, let water slowly percolate. There will
in the first place be a distinct parting of the substances that are the
most widely contrasted in their relations to the acting forces: the
soluble will be carried away; the insoluble will remain behind. Further,
some separation, though a less definite one, will be effected among the
soluble substances; since the first part of the current will remove the
most soluble substances in the largest amounts, and after these have
been all dissolved, the current will still continue to bring out the
remaining less soluble substances. Even the undissolved matters will
have simultaneously undergone a certain segregation; for the percolating
fluid will carry down the minute fragments from among the large ones,
and will deposit those of small specific gravity in one place, and those
of great specific gravity in another.       To complete the elucidation
we must glance at the obverse fact; namely, that mixed units which
differ but slightly, are moved in but slightly-different ways by
incident forces, and can therefore be separated only by such adjustments
of the incident forces as allow slight differences to become appreciable
factors in the result. This truth is made manifest by antithesis in the
instances just given; but it may be made much more manifest by a few
such instances as those which chemical analysis supplies in abundance.
The parting of alcohol from water by distillation is a good one. Here we
have atoms consisting of oxygen and hydrogen, mingled with atoms
consisting of oxygen, hydrogen, and carbon. The two orders of atoms have
a considerable similarity of nature: they similarly maintain a fluid
form at ordinary temperatures; they similarly become gaseous more and
more rapidly as the temperature is raised; and they boil at points not
very far apart. Now this comparative likeness of the atoms is
accompanied by difficulty in segregating them. If the mixed fluid is
unduly heated, much water distils over with the alcohol: it is only
within a narrow range of temperature, that the one set of atoms are
driven off rather than the others; and even then not a few of the others
accompany them. The most interesting and instructive example, however,
is furnished by certain phenomena of crystallization. When several salts
that have little analogy of constitution, are dissolved in the same body
of water, they are separated without much trouble, by crystallization:
their respective units moved towards each other, as physicists suppose,
by polar forces, segregate into crystals of their respective kinds. The
crystals of each salt do, indeed, usually contain certain small amounts
of the other salts present in the solution�especially when the
crystallization has been rapid; but from these other salts they are
severally freed by repeated resolutions and crystallizations. Mark now,
however, that the reverse is the case when the salts contained in the
same body of water are chemically homologous. The nitrates of baryta and
lead, or the sulphates of zinc, soda, and magnesia, unite in the same
crystals; nor will they crystallize separately if these crystals be
dissolved afresh, and afresh crystallized, even with great care. On
seeking the cause of this anomaly, chemists found that such salts were
isomorphous�that their atoms, though not chemically identical, were
identical in the proportions of acid, base, and water, composing them,
and in their crystalline forms: whence it was inferred that their atoms
are nearly alike in structure. Thus is clearly illustrated the truth,
that units of unlike kinds are differentiated and integrated with a
readiness proportionate to the degree of their unlikeness. In the first
case we see that being dissimilar in their forms, but similar in so far
as they are soluble in water of a certain temperature, the atoms
segregate, though imperfectly. In the second case we see that the atoms,
having not only the likeness implied by solubility in the same
menstruum, but also a great likeness of structure, do not segregate�are
differentiated and integrated only under quite special conditions, and
then very incompletely. That is, the incident force of mutual polarity
impresses unlike motions on the mixed units in proportion as they are
unlike; and therefore, in proportion as they are unlike, tends to
deposit them in separate places.

There is a converse cause of segregation, which it is needless here to
treat of with equal fulness. If different units acted on by the same
force, must be differently moved; so, too, must units of the same kind
be differently moved by different forces. Supposing some group of units
forming part of a homogeneous aggregate, are unitedly exposed to a force
that is unlike in amount or direction to the force acting on the rest of
the aggregate; then this group of units will separate from the rest,
provided that, of the force so acting on it, there remains any portion
not dissipated in molecular vibrations, nor absorbed in producing
molecular re-arrangements. After all that has been said above, this
proposition needs no defence.

Before ending our preliminary exposition, a complementary truth must be
specified; namely, that mixed forces are segregated by the reaction of
uniform matters, just as mixed matters are segregated by the action of
uniform forces. Of this truth a complete and sufficient illustration is
furnished by the dispersion of refracted light. A beam of light, made up
of ethereal undulations of different orders, is not uniformly deflected
by a homogeneous refracting body; but the different orders of
undulations it contains, are deflected at different angles: the result
being that these different orders of undulations are separated and
integrated, and so produce what we know as the colours of the spectrum.
A segregation of another kind occurs when rays of light traverse an
obstructing medium. Those rays which consist of comparatively short
undulations, are absorbed before those which consist of comparatively
long ones; and the red rays, which consist of the longest undulations,
alone penetrate when the obstruction is very great. How, conversely,
there is produced a separation of like forces by the reaction of unlike
matters, is also made manifest by the phenomena of refraction: since
adjacent and parallel beams of light, falling on, and passing through,
unlike substances, are made to diverge.

                  *       *       *       *       *

§ 124. On the assumption of their nebular origin, stars and planets
exemplify that cause of material integration last assigned�the action of
unlike forces on like units.

In a preceding chapter (§ 110) we saw that if matter ever existed in a
diffused form, it could not continue uniformly distributed, but must
break up into masses. It was shown that in the absence of a perfect
balance of mutual attractions among atoms dispersed through unlimited
space, there must arise breeches of continuity throughout the aggregate
formed by them, and a concentration of it towards centres of dominant
attraction. Where any such breech of continuity occurs, and the atoms
that were before adjacent separate from each other; they do so in
consequence of a difference in the forces to which they are respectively
subject. The atoms on the one side of the breech are exposed to a
certain surplus attraction in the direction in which they begin to move;
and those on the other to a surplus attraction in the opposite
direction. That is, the adjacent groups of like units are exposed to
unlike resultant forces; and accordingly separate and integrate.

The formation and detachment of a nebulous ring, illustrates the same
general principle. To conclude, as Laplace did, that the equatorial
portion of a rotating nebulous spheroid, will, during concentration,
acquire a centrifugal force sufficient to prevent it from following the
rest of the contracting mass, is to conclude that such portions will
remain behind as are in common subject to a certain differential force.
The line of division between the ring and the spheroid, must be a line
inside of which the aggregative force is greater than the force
resisting aggregation; and outside of which the force resisting
aggregation is greater than the aggregative force. Hence the alleged
process conforms to the law that among like units, separation and
integration is produced by the action of unlike forces.

Astronomical phenomena do not furnish any other than these hypothetical
examples. In its present comparatively settled condition, the Solar
System exhibits no direct evidence of progressing integration: unless
indeed under the insignificant form of the union of meteoric masses with
the Earth, and, occasionally perhaps, of cometary matter with the Sun.

                  *       *       *       *       *

§ 125. Those geologic changes usually classed as aqueous, display under
numerous forms the segregation of unlike units by a uniform incident
force. On sea-shores, the waves are ever sorting-out and separating the
mixed materials against which they break. From each mass of fallen
cliff, the rising and ebbing tide carries away all those particles which
are so small as to remain long suspended in the water; and, at some
distance from shore, deposits them in the shape of fine sediment. Large
particles, sinking with comparative rapidity, are accumulated into beds
of sand near low water-mark. The coarse grit and small pebbles collect
together on the incline up which the breakers rush. And on the top lie
the larger stones and boulders. Still more specific segregations may
occasionally be observed. Flat pebbles, produced by the breaking down of
laminated rock, are sometimes separately collected in one part of a
shingle bank. On this shore the deposit is wholly of mud; on that it is
wholly of sand. Here we find a sheltered cove filled with small pebbles
almost of one size; and there, in a curved bay one end of which is more
exposed than the other, we see a progressive increase in the massiveness
of the stones as we walk from the less exposed to the more exposed end.
Indeed, our sedimentary strata form one vast series of illustrations of
the alleged law. Trace the history of each deposit, and we are quickly
led down to the fact, that mixed fragments of matter, differing in their
sizes or weights, are, when exposed to the momentum and friction of
water, joined with the attraction of the Earth, selected from each
other, and united into groups of comparatively like fragments. We see
that, other things equal, the separation is definite in proportion as
the differences of the units are marked; and that, under the action of
the same aggregate of forces, the most widely unlike units are most
widely removed from each other.

Among igneous changes we do not find so many examples of the process
described. When specifying the conditions to Evolution, it was pointed
out (§ 104) that molecular vibration exceeding a certain intensity, does
not permit those integrations which result from the action of minor
differential forces. Nevertheless, geological phenomena of this order
are not barren of illustrations. Where the mixed matters composing the
Earth�s crust have been raised to a very high temperature, segregation
habitually takes place as the temperature diminishes. Sundry of the
substances that escape in a gaseous form from volcanoes, sublime into
crystals on coming against cool surfaces; and solidifying, as these
substances do, at different temperatures, they are deposited at
different parts of the crevices through which they are emitted together.
The best illustration, however, is furnished by the changes that occur
during the slow cooling of igneous rock. When, through one of the
fractures from time to time made in the solid shell which forms the
Earth�s crust, a portion of the molten nucleus is extruded; and when
this is cooled with comparative rapidity, through free radiation and
contact with cold masses; it forms a substance known as trap or basalt�a
substance that is uniform in texture, though made up of various
ingredients. But when, not escaping through the superficial strata, such
a portion of the molten nucleus is slowly cooled, it becomes what we
know as granite: the mingled particles of quartz, feldspar, and mica,
being kept for a long time in a fluid and semi-fluid state�a state of
comparative mobility�undergo those changes of position which the forces
impressed on them by their fellow units necessitate. Having time in
which to generate the requisite motions of the atoms, the differential
forces arising from mutual polarity, segregate the quartz, feldspar, and
mica, into crystals. How completely this is dependent on the
long-continued agitation of the mixed particles, and consequent
long-continued mobility by small differential forces, is proved by the
fact that in granite dykes, the crystals in the centre of the mass,
where the fluidity or semi-fluidity continued for a longer time, are
much larger than those at the sides, where contact with the neighbouring
rock caused more rapid cooling and solidification.

                  *       *       *       *       *

§ 126. The actions going on throughout an organism are so involved and
subtle, that we cannot expect to identify the particular forces by which
particular integrations are effected. Among the few instances admitting
of tolerably definite interpretation, the best are those in which
mechanical pressures and tensions are the agencies at work. We shall
discover several on studying the bony frame of the higher animals.

The vertebral column of a man, is subject, as a whole, to certain
general strains�the weight of the body, together with the reactions
involved by all considerable muscular efforts; and in conformity with
this, it has a certain general integration. At the same time, being
exposed to different forces in the course of those lateral bendings
which the movements necessitate, its parts retain a certain
separateness. And if we trace up the development of the vertebral column
from its primitive form of a cartilaginous cord in the lowest fishes, we
see that, throughout, it maintains an integration corresponding to the
unity of the incident forces, joined with a division into segments
corresponding to the variety of the incident forces.       Each segment,
considered apart, exemplifies the truth more simply. A vertebra is not a
single bone, but consists of a central mass with sundry appendages or
processes; and in rudimentary types of vertebræ, those appendages are
quite separate from the central mass, and, indeed, exist before it makes
its appearance. But these several independent bones, constituting a
primitive spinal segment, are subject to a certain aggregate of forces
which agree more than they differ: as the fulcrum to a group of muscles
habitually acting together, they perpetually undergo certain reactions
in common. And accordingly, we see that in the course of development
they gradually coalesce.       Still clearer is the illustration
furnished by spinal segments that become fused together where they are
together exposed to some predominant strain. The sacrum consists of a
group of vertebræ firmly united. In the ostrich and its congeners there
are from seventeen to twenty sacral vertebræ; and besides being
confluent with each other, these are confluent with the iliac bones,
which run on each side of them. If now we assume these vertebræ to have
been originally separate, as they still are in the embryo bird; and if
we consider the mechanical conditions to which they must in such case
have been exposed; we shall see that their union results in the alleged
way. For through these vertebræ the entire weight of the body is
transferred to the legs: the legs support the pelvic arch; the pelvic
arch supports the sacrum; and to the sacrum is articulated the rest of
the spine, with all the limbs and organs attached to it. Hence, if
separate, the sacral vertebræ must be held firmly together by
strongly-contracted muscles; and must, by implication, be prevented from
partaking in those lateral movements which the other vertebræ
undergo�they must be subject to a common strain, while they are
preserved from strains which would affect them differently; and so they
fulfil the conditions under which integration occurs.       But the
cases in which cause and effect are brought into the most obvious
relation, are supplied by the limbs. The metacarpal bones (those which
in man support the palm of the hand) are separate from each other in the
majority of mammalia: the separate actions of the toes entailing on them
slight amounts of separate movements. This is not so however in the
ox-tribe and the horse-tribe. In the ox-tribe, only the middle
metacarpals (third and fourth) are developed; and these, attaining
massive proportions, coalesce to form the cannon bone. In the
horse-tribe, the integration is what we may distinguish as indirect: the
second and fourth metacarpals are present only as rudiments united to
the sides of the third, while the third is immensely developed; thus
forming a cannon bone which differs from that of the ox in being a
single cylinder, instead of two cylinders fused together. The metatarsus
in these quadrupeds exhibits parallel changes. Now each of these
metamorphoses occurs where the different bones grouped together have no
longer any different functions, but retain only a common function. The
feet of oxen and horses are used solely for locomotion�are not put like
those of unguiculate mammals to purposes which involve some relative
movements of the metacarpals. Thus there directly or indirectly results
a single mass of bone where the incident force is single. And for the
inference that these facts have a causal connexion, we find confirmation
throughout the entire class of birds; in the wings and legs of which,
like integrations are found under like conditions.       While this
sheet is passing through the press, a fact illustrating this general
truth in a yet more remarkable manner, has been mentioned to me by Prof.
Huxley; who kindly allows me to make use of it while still unpublished
by him. The _Glyptodon_, an extinct mammal found fossilized in South
America, has long been known as a large uncouth creature allied to the
Armadillo, but having a massive dermal armour consisting of polygonal
plates closely fitted together so as to make a vast box, inclosing the
body in such way as effectually to prevent it from being bent, laterally
or vertically, in the slightest degree. This bony box, which must have
weighed several hundred-weight, was supported on the spinous processes
of the vertebræ, and on the adjacent bones of the pelvic and thoracic
arches. And the significant fact now to be noted, is, that here, where
the trunk vertebræ were together exposed to the pressure of this heavy
dermal armour, at the same time that, by its rigidity, they were
preserved from all relative movements, the entire series of them were
united into one solid, continuous bone.

The formation and maintenance of a species, considered as an assemblage
of similar organisms, is interpretable in an analogous way. We have
already seen that in so far as the members of a species are subject to
different sets of incident forces, they are differentiated, or divided
into varieties. And here it remains to add that in so far as they are
subject to like sets of incident forces, they are integrated, or reduced
to, and kept in, the state of a uniform aggregate. For by the process of
�natural selection,� there is a continual purification of each species
from those individuals which depart from the common type in ways that
unfit them for the conditions of their existence. Consequently, there is
a continual leaving behind of those individuals which are in all
respects fit for the conditions of their existence; and are therefore
very nearly alike. The circumstances to which any species is exposed,
being, as we before saw, an involved combination of incident forces; and
the members of the species having mixed with them some that differ more
than usual from the average structure required for meeting these forces;
it results that these forces are constantly separating such divergent
individuals from the rest, and so preserving the uniformity of the
rest�keeping up its integrity as a species. Just as the changing autumn
leaves are picked out by the wind from among the green ones around them,
or just as, to use Prof. Huxley�s simile, the smaller fragments pass
through the sieve while the larger are kept back; so, the uniform
incidence of external forces affects the members of a group of organisms
similarly in proportion as they are similar, and differently in
proportion as they are different; and thus is ever segregating the like
by parting the unlike from them. Whether these separated members are
killed off, as mostly happens, or whether, as otherwise happens, they
survive and multiply into a distinct variety, in consequence of their
fitness to certain partially unlike conditions, matters not to the
argument. The one case conforms to the law, that the unlike units of an
aggregate are differentiated and integrated when uniformly subject to
the same incident forces; and the other to the converse law, that the
like units of an aggregate are differentiated and integrated when
subject to different incident forces. And on consulting Mr. Darwin�s
remarks on divergence of character, it will be seen that the
segregations thus caused tend ever to become more definite.

                  *       *       *       *       *

§ 127. Mental evolution under one of its leading aspects, we found to
consist in the formation of groups of like objects and like
relations�a differentiation of the various things originally
confounded together in one assemblage, and an integration of each
separate order of things into a separate group (§ 113). Here it
remains to point out that while unlikeness in the incident forces is
the cause of such differentiations, likeness in the incident forces is
the cause of such integrations. For what is the process through which
classifications are established? At first, in common with the
uninitiated, the botanist recognizes only such conventional divisions
as those which agriculture has established�distinguishes a few
vegetables and cereals, and groups the rest together into the one
miscellaneous aggregate of wild plants. How do these wild plants
become grouped in his mind into orders, genera, and species? Each
plant he examines yields him a certain complex impression. Every now
and then he picks up a plant like one before seen; and the recognition
of it is the production in him of a like connected group of
sensations, by a like connected group of attributes. That is to say,
there is produced throughout the nerves concerned, a combined set of
changes, similar to a combined set of changes before produced.
Considered analytically, each such combined set of changes is a
combined set of molecular modifications wrought in the affected part
of the organism. On every repetition of the impression, a like
combined set of molecular modifications is superposed on the previous
ones, and makes them greater: thus generating an internal idea
corresponding to these similar external objects. Meanwhile, another
kind of plant produces in the brain of the botanist another set of
combined changes or molecular modifications�a set which does not agree
with and deepen the one we have been considering, but disagrees with
it; and by repetition of such there is generated a different idea
answering to a different species.       What now is the nature of this
process expressed in general terms? On the one hand there are the like
and unlike things from which severally emanate the groups of forces by
which we perceive them. On the other hand, there are the organs of
sense and percipient centres, through which, in the course of
observation, these groups of forces pass. In passing through these
organs of sense and percipient centres, the like groups of forces are
segregated, or separated from the unlike groups of forces; and each
such differentiated and integrated series of groups of forces,
answering to an external genus or species, constitutes a state of
consciousness which we call our idea of the genus or species. We
before saw that as well as a separation of mixed matters by the same
force, there is a separation of mixed forces by the same matter; and
here we may further see that the unlike forces so separated, work
unlike structural changes in the aggregate that separates
them�structural changes each of which thus represents, and is
equivalent to, the integrated series of motions that has produced it.

By a parallel process, the connexions of co-existence and sequence among
impressions, become differentiated and integrated simultaneously with
the impressions themselves. When two phenomena that have been
experienced in a given order, are repeated in the same order, those
nerves which before were affected by the transition are again affected;
and such molecular modification as they received from the first motion
propagated through them, is increased by this second motion along the
same route. Each such motion works a structural alteration, which, in
conformity with the general law set forth in Chapter X., involves a
diminution of the resistance to all such motions that afterwards occur.
The integration of these successive motions (or more strictly, the
permanently effective portions of them expended in overcoming
resistance) thus becomes the cause of, and the measure of, the mental
connexion between the impressions which the phenomena produce.
Meanwhile, phenomena that are recognized as different from these, being
phenomena that therefore affect different nervous elements, will have
their connexions severally represented by motions along other routes;
and along each of these other routes, the nervous discharges will
severally take place with a readiness proportionate to the frequency
with which experience repeats the connexion of phenomena. The
classification of relations must hence go on _pari passu_ with the
classification of the related things. In common with the mixed
sensations received from the external world, the mixed relations it
presents, cannot be impressed on the organism without more or less
segregation of them resulting. And through this continuous
differentiation and integration of changes or motions, which constitutes
nervous function, there is gradually wrought that differentiation and
integration of matter, which constitutes nervous structure.

                  *       *       *       *       *

§ 128. In social evolution, the collecting together of the like and the
separation of the unlike, by incident forces, is primarily displayed in
the same manner as we saw it to be among groups of inferior creatures.
The human races tend to differentiate and integrate, as do races of
other living forms.       Of the forces which effect and maintain the
segregations of mankind, may first be named those external ones which we
class as physical conditions. The climate and food that are favourable
to an indigenous people, are more or less detrimental to a people of
different bodily constitution, coming from a remote part of the Earth.
In tropical regions the northern races cannot permanently exist: if not
killed off in the first generation, they are so in the second; and, as
in India, can maintain their footing only by the artificial process of
continuous immigration and emigration. That is to say, the external
forces acting equally on the inhabitants of a given locality, tend to
expel all who are not of a certain type; and so to keep up the
integration of those who are of that type. Though elsewhere, as among
European nations, we see a certain amount of permanent intermixture,
otherwise brought about, we still see that this takes place between
races of not very different types, that are naturalized to not very
different conditions.       The other forces conspiring to produce these
national integrations, are those mental ones which show themselves in
the affinities of men for others like themselves. Emigrants usually
desire to get back among their own people; and where their desire does
not take effect, it is only because the restraining ties are too great.
Units of one society who are obliged to reside in another, very
generally form colonies in the midst of that other�small societies of
their own. Races which have been artificially severed, show strong
tendencies to re-unite. Now though these integrations that result from
the mutual affinities of kindred men, do not seem interpretable as
illustrations of the general principle above enunciated, they really are
thus interpretable. When treating of the direction of motion (§ 91), it
was shown that the actions performed by men for the satisfaction of
their wants, were always motions along lines of least resistance. The
feelings characterizing a member of a given race, are feelings which get
complete satisfaction only among other members of that race�a
satisfaction partly derived from sympathy with those having like
feelings, but mainly derived from the adapted social conditions which
grow up where such feelings prevail. When, therefore, a citizen of any
nation is, as we see, attracted towards others of his nation, the
rationale is, that certain agencies which we call desires, move him in
the direction of least resistance. Human motions, like all other
motions, being determined by the distribution of forces, it follows that
such integrations of races as are not produced by incident external
forces, are produced by forces which the units of the races exercise on
each other.

During the development of each society, we see analogous segregations
caused in analogous ways. A few of them result from minor natural
affinities; but those most important ones which constitute political and
industrial organization, result from the union of men in whom
similarities have been produced by education�using education in its
widest sense, as comprehending all processes by which citizens are
moulded to special functions. Men brought up to bodily labour, are men
who have had wrought in them a certain likeness�a likeness which, in
respect of their powers of action, obscures and subordinates their
natural differences. Those trained to brain-work, have acquired a
certain other community of character which makes them, as social units,
more like each other than like those trained to manual occupations. And
there arise class-integrations answering to these superinduced
likenesses. Much more definite integrations take place among the much
more definitely assimilated members of any class who are brought up to
the same calling. Even where the necessities of their work forbid
concentration in one locality, as among artizans happens with masons and
brick-layers, and among traders happens with the retail distributors,
and among professionals happens with the medical men; there are not
wanting Operative Builders Unions, and Grocers Societies, and Medical
Associations, to show that these artificially-assimilated citizens
become integrated as much as the conditions permit. And where, as among
the manufacturing classes, the functions discharged do not require the
dispersion of the citizens thus artificially assimilated, there is a
progressive aggregation of them in special localities; and a consequent
increase in the definiteness of the industrial divisions.       If now
we seek the causes of these integrations, considered as results of force
and motion, we find ourselves brought to the same general principle as
before. This likeness generated in any class or subclass by training, is
an aptitude acquired by its members for satisfying their wants in like
ways. That is, the occupation to which each man has been brought up, has
become to him, in common with those similarly brought up, a line of
least resistance. Hence under that pressure which determines all men to
activity, these similarly-modified social units are similarly affected,
and tend to take similar courses. If then there be any locality which,
either by its physical peculiarities or by peculiarities wrought on it
during social evolution, is rendered a place where a certain kind of
industrial action meets with less resistance than elsewhere; it follows
from the law of direction of motion that those social units who have
been moulded to this kind of industrial action, will move towards this
place, or become integrated there. If, for instance, the proximity of
coal and iron mines to a navigable river, gives to Glasgow a certain
advantage in the building of iron ships�if the total labour required to
produce the same vessel, and get its equivalent in food and clothing, is
less there than elsewhere; a concentration of iron-ship builders is
produced at Glasgow: either by keeping there the population born to
iron-ship building; or by immigration of those elsewhere engaged in it;
or by both�a concentration that would be still more marked did not other
districts offer counter-balancing facilities. The principle equally
holds where the occupation is mercantile instead of manufacturing.
Stock-brokers cluster together in the city, because the amount of effort
to be severally gone through by them in discharging their functions, and
obtaining their profits, is less there than in other localities. A place
of exchange having once been established, becomes a place where the
resistance to be overcome by each is less than elsewhere; and the
pursuit of the course of least resistance by each, involves their
aggregation around this place.

Of course, with units so complicated as those which constitute a
society, and with forces so involved as those which move them, the
resulting differentiations and integrations must be far more entangled,
or far less definite, than those we have hitherto considered. But though
there may be pointed out many anomalies which at first sight seem
inconsistent with the alleged law, a closer study shows that they are
but subtler illustrations of it. For men�s likenesses being of various
kinds, lead to various order of integration. There are likenesses of
disposition, likenesses of taste, likenesses produced by intellectual
culture, likenesses that result from class-training, likenesses of
political feeling; and it needs but to glance round at the
caste-divisions, the associations for philanthropic, scientific, and
artistic purposes, the religious parties and social cliques; to see that
some species of likeness among the component members of each body
determines their union. Now these different integrations, by traversing
each other, and often by their indirect antagonism, more or less obscure
each other; and prevent any one kind of integration from becoming
complete. Hence the anomalies referred to. But if this cause of
incompleteness be duly borne in mind, social segregations will be seen
to conform entirely to the same principle as all other segregations.
Analysis will show that either by external incident forces, or by what
we may in a sense regard as mutual polarity, there are ever being
produced in society integrations of those units which have either a
natural likeness or a likeness generated by training.

                  *       *       *       *       *

§ 129. Can the general truth thus variously illustrated be deduced from
the persistence of force, in common with foregoing ones? Probably the
exposition at the beginning of the chapter will have led most readers to
conclude that it can be so deduced.

The abstract propositions involved are these:�First, that like units,
subject to a uniform force capable of producing motion in them, will be
moved to like degrees in the same direction. Second, that like units if
exposed to unlike forces capable of producing motion in them, will be
differently moved�moved either in different directions or to different
degrees in the same direction. Third, that unlike units if acted on by a
uniform force capable of producing motion in them, will be differently
moved�moved either in different directions or to different degrees in
the same direction. Fourth, that the incident forces themselves must be
affected in analogous ways: like forces falling on like units must be
similarly modified by the conflict; unlike forces falling on like units
must be dissimilarly modified; and like forces falling on unlike units
must be dissimilarly modified. These propositions admit of reduction to
a still more abstract form. They all of them amount to this:�that in the
actions and reactions of force and matter, an unlikeness in either of
the factors necessitates an unlikeness in the effects; and that in the
absence of unlikeness in either of the factors the effects must be
alike.

When thus generalized, the immediate dependence of these propositions on
the persistence of force, becomes obvious. Any two forces that are not
alike, are forces which differ either in their amounts or directions or
both; and by what mathematicians call the resolution of forces, it may
be proved that this difference is constituted by the presence in the one
of some force not present in the other. Similarly, any two units or
portions of matter which are unlike in size, weight, form, or other
attribute, can be known by us as unlike only through some unlikeness in
the forces they impress on our consciousness; and hence this unlikeness
also, is constituted by the presence in the one of some force or forces
not present in the other. Such being the common nature of these
unlikenesses, what is the inevitable corollary? Any unlikeness in the
incident forces, where the things acted on are alike, must generate a
difference between the effects; since otherwise, the differential force
produces no effect, and force is not persistent. Any unlikeness in the
things acted on, where the incident forces are alike, must generate a
difference between the effects; since otherwise, the differential force
whereby these things are made unlike, produces no effect, and force is
not persistent. While, conversely, if the forces acting and the things
acted on, are alike, the effects must be alike; since otherwise, a
differential effect can be produced without a differential cause, and
force is not persistent.

Thus these general truths being necessary implications of the
persistence of force, all the re-distributions above traced out as
characterizing Evolution in its various phases, are also implications of
the persistence of force. Such portions of the permanently effective
forces acting on any aggregate, as produce sensible motions in its
parts, cannot but work the segregations which we see take place. If of
the mixed units making up such aggregate, those of the same kind have
like motions impressed on them by a uniform force, while units of
another kind are moved by this uniform force in ways more or less unlike
the ways in which those of the first kind are moved, the two kinds must
separate and integrate. If the units are alike and the forces unlike, a
division of the differently affected units is equally necessitated. Thus
there inevitably arises the demarcated grouping which we everywhere see.
By virtue of this segregation that grows ever more decided while there
remains any possibility of increasing it, the change from uniformity to
multiformity is accompanied by a change from indistinctness in the
relations of parts to distinctness in the relations of parts. As we
before saw that the transformation of the homogeneous into the
heterogeneous is inferrable from that ultimate truth which transcends
proof; so we here see, that from this same truth is inferrable the
transformation of an indefinite homogeneity into a definite
heterogeneity.




                              CHAPTER XVI.
                             EQUILIBRATION.


§ 130. And now towards what do these changes tend? Will they go on for
ever? or will there be an end to them? Can things increase in
heterogeneity through all future time? or must there be a degree which
the differentiation and integration of Matter and Motion cannot pass? Is
it possible for this universal metamorphosis to proceed in the same
general course indefinitely? or does it work towards some ultimate
state, admitting no further modification of like kind? The last of these
alternative conclusions is that to which we are inevitably driven.
Whether we watch concrete processes, or whether we consider the question
in the abstract, we are alike taught that Evolution has an impassable
limit.

The re-distributions of matter that go on around us, are ever being
brought to conclusions by the dissipation of the motions which effect
them. The rolling stone parts with portions of its momentum to the
things it strikes, and finally comes to rest; as do also, in like
manner, the various things it has struck. Descending from the clouds and
trickling over the Earth�s surface till it gathers into brooks and
rivers, water, still running towards a lower level, is at last arrested
by the resistance of other water that has reached the lowest level. In
the lake or sea thus formed, every agitation raised by a wind or the
immersion of a solid body, propagates itself around in waves that
diminish as they widen, and gradually become lost to observation in
motions communicated to the atmosphere and the matter on the shores. The
impulse given by a player to the harp-string, is transformed through its
vibrations into aerial pulses; and these, spreading on all sides, and
weakening as they spread, soon cease to be perceptible; and finally die
away in generating thermal undulations that radiate into space. Equally
in the cinder that falls out of the fire, and in the vast masses of
molten lava ejected by a volcano, we see that the molecular agitation
known to us as heat, disperses itself by radiation; so that however
great its amount, it inevitably sinks at last to the same degree as that
existing in surrounding bodies. And if the actions observed be
electrical or chemical, we still find that they work themselves out in
producing sensible or insensible movements, that are dissipated as
before; until quiescence is eventually reached.       The proximate
rationale of the process exhibited under these several forms, lies in
the fact dwelt on when treating of the Multiplication of Effects, that
motions are ever being decomposed into divergent motions, and these into
re-divergent motions. The rolling stone sends off the stones it hits in
directions differing more or less from its own; and they do the like
with the things they hit. Move water or air, and the movement is quickly
resolved into radiating movements. The heat produced by pressure in a
given direction, diffuses itself by undulations in all directions; and
so do the light and electricity similarly generated. That is to say,
these motions undergo division and subdivision; and by continuance of
this process without limit, they are, though never lost, gradually
reduced to insensible motions.

In all cases then, there is a progress toward equilibration. That
universal co-existence of antagonist forces which, as we before saw,
necessitates the universality of rhythm, and which, as we before saw,
necessitates the decomposition of every force into divergent forces, at
the same time necessitates the ultimate establishment of a balance.
Every motion being motion under resistance, is continually suffering
deductions; and these unceasing deductions finally result in the
cessation of the motion.

The general truth thus illustrated under its simplest aspect, we must
now look at under those more complex aspects it usually presents
throughout Nature. In nearly all cases, the motion of an aggregate is
compound; and the equilibration of each of its components, being carried
on independently, does not affect the rest. The ship�s bell that has
ceased to vibrate, still continues those vertical and lateral
oscillations caused by the ocean-swell. The water of the smooth stream
on whose surface have died away the undulations caused by the rising
fish, moves as fast as before onward to the sea. The arrested bullet
travels with undiminished speed round the Earth�s axis. And were the
rotation of the Earth destroyed, there would not be implied any
diminution of the Earth�s movement with respect to the Sun and other
external bodies. So that in every case, what we regard as equilibration
is a disappearance of some one or more of the many movements which a
body possesses, while its other movements continue as before.       That
this process may be duly realized and the state of things towards which
it tends fully understood, it will be well here to cite a case in which
we may watch this successive equilibration of combined movements more
completely than we can do in those above instanced. Our end will best be
served, not by the most imposing, but by the most familiar example. Let
us take that of the spinning top. When the string which has been wrapped
round a top�s axis is violently drawn off, and the top falls on to the
table, it usually happens that besides the rapid rotation, two other
movements are given to it. A slight horizontal momentum, unavoidably
impressed on it when leaving the handle, carries it away bodily from the
place on which it drops; and in consequence of its axis being more or
less inclined, it falls into a certain oscillation, described by the
expressive though inelegant word��wabbling.� These two subordinate
motions, variable in their proportions to each other and to the chief
motion, are commonly soon brought to a close by separate processes of
equilibration. The momentum which carries the top bodily along the
table, resisted somewhat by the air, but mainly by the irregularities of
the surface, shortly disappears; and the top thereafter continues to
spin on one spot. Meanwhile, in consequence of that opposition which the
axial momentum of a rotating body makes to any change in the plane of
rotation, (so beautifully exhibited by the gyroscope,) the �wabbling�
diminishes; and like the other is quickly ended. These minor motions
having been dissipated, the rotatory motion, interfered with only by
atmospheric resistance and the friction of the pivot, continues some
time with such uniformity that the top appears stationary: there being
thus temporarily established a condition which the French mathematicians
have termed _equilibrium mobile_. It is true that when the axial
velocity sinks below a certain point, new motions commence, and increase
till the top falls; but these are merely incidental to a case in which
the centre of gravity is above the point of support. Were the top,
having an axis of steel, to be suspended from a surface adequately
magnetized, all the phenomena described would be displayed, and the
moving equilibrium having been once arrived at, would continue until the
top became motionless, without any further change of position.       Now
the facts which it behoves us here to observe, are these. First, that
the various motions which an aggregate possesses are separately
equilibrated: those which are smallest, or which meet with the greatest
resistance, or both, disappearing first; and leaving at last, that which
is greatest, or meets with least resistance, or both. Second, that when
the aggregate has a movement of its parts with respect to each other,
which encounters but little external resistance, there is apt to be
established an _equilibrium mobile_. Third, that this moving equilibrium
eventually lapses into complete equilibrium.

Fully to comprehend the process of equilibration, is not easy; since we
have simultaneously to contemplate various phases of it. The best course
will be to glance separately at what we may conveniently regard as its
four different orders.       The first order includes the comparatively
simple motions, as those of projectiles, which are not prolonged enough
to exhibit their rhythmical character; but which, being quickly divided
and subdivided into motions communicated to other portions of matter,
are presently dissipated in the rhythm of ethereal undulations.       In
the second order, comprehending the various kinds of vibration or
oscillation as usually witnessed, the motion is used up in generating a
tension which, having become equal to it or momentarily equilibrated
with it, thereupon produces a motion in the opposite direction, that is
subsequently equilibrated in like manner: thus causing a visible rhythm,
that is, however, soon lost in invisible rhythms.       The third order
of equilibration, not hitherto noticed, obtains in those aggregates
which continually receive as much motion as they expend. The steam
engine (and especially that kind which feeds its own furnace and boiler)
supplies an example. Here the force from moment to moment dissipated in
overcoming the resistance of the machinery driven, is from moment to
moment replaced from the fuel; and the balance of the two is maintained
by a raising or lowering of the expenditure according to the variation
of the supply: each increase or decrease in the quantity of steam,
resulting in a rise or fall of the engine�s movement, such as brings it
to a balance with the increased or decreased resistance. This, which we
may fitly call the _dependent_ moving equilibrium, should be specially
noted; since it is one that we shall commonly meet with throughout
various phases of Evolution.       The equilibration to be distinguished
as of the fourth order, is the _independent_ or perfect moving
equilibrium. This we see illustrated in the rhythmical motions of the
Solar System; which, being resisted only by a medium of inappreciable
density, undergo no sensible diminution in such periods of time as we
can measure.

All these kinds of equilibration may, however, from the highest point of
view, be regarded as different modes of one kind. For in every case the
balance arrived at is relative, and not absolute�is a cessation of the
motion of some particular body in relation to a certain point or points,
involving neither the disappearance of the relative motion lost, which
is simply transformed into other motions, nor a diminution of the body�s
motions with respect to other points. Thus understanding equilibration,
it manifestly includes that _equilibrium mobile_, which at first sight
seems of another nature. For any system of bodies exhibiting, like those
of the Solar System, a combination of balanced rhythms, has this
peculiarity;�that though the constituents of the system have relative
movements, the system as a whole has no movement. The centre of gravity
of the entire group remains fixed. Whatever quantity of motion any
member of it has in any direction, is from moment to moment
counter-balanced by an equivalent motion in some other part of the group
in an opposite direction; and so the aggregate matter of the group is in
a state of rest. Whence it follows that the arrival at a state of moving
equilibrium, is the disappearance of some movement which the aggregate
had in relation to external things, and a continuance of those movements
only which the different parts of the aggregate have in relation to each
other. Thus generalizing the process, it becomes clear that all forms of
equilibration are intrinsically the same; since in every aggregate, it
is the centre of gravity only that loses its motion: the constituents
always retaining some motion with respect to each other�the motion of
molecules if none else.

Those readers who happen to bear in mind a proposition concerning the
functional characteristics of Evolution, which was set forth in Chapter
XII, will probably regard it as wholly at variance with that set forth
in this Chapter. It was there alleged that throughout Evolution,
integration of matter is accompanied by integration of such motion as
the matter previously had; and that thus there is a transformation of
diffused motion into aggregated motion, parallel to the transformation
of diffused matter into aggregated matter. Here however, it is asserted
that every aggregate motion is constantly undergoing diffusion�every
integrated motion undergoing perpetual disintegration. And so the motion
of masses, which before was said gradually to arise out of molecular
motion, is here said to be gradually lost in molecular motion. Doubtless
these statements, if severally accepted without qualification, are
contradictory. Neither of them, however, expresses the whole truth. Each
needs the other as its indispensable complement. It is quite true, as
before alleged, that there goes on an integration of motion
corresponding to the integration of matter; and that this essential
characteristic of Evolution, functionally considered, is clearly
displayed in proportion as the Evolution is active. But the
disintegration of motion, which, as we before saw, constitutes
Dissolution, functionally considered, is all along going on; and though
at first it forms but a small deduction from the change constituting
Evolution, it gradually becomes equal to it, and eventually exceeding
it, entails reverse changes. The aggregation of matter never being
complete, but leaving behind less aggregated or unaggregated matter, in
the shape of liquid, aeriform, or ethereal media; it results that from
the beginning, the integrated motion of integrated masses, is ever being
obstructed by these less integrated or unintegrated media. So that
though while the integration of matter is rapidly going on, there is an
increase of integrated motion, spite of the deductions thus continually
made from it, there comes a time when the integration of matter and
consequently of motion, ceases to increase, or increases so slowly that
the deductions counterbalance it; and thenceforth these begin to
decrease it, and, by its perpetual diffusion, to bring about a relative
equilibration. From the beginning, the process of Evolution is
antagonized by a process of Dissolution; and while the first for a long
time predominates, the last finally arrests and reverses it.

Returning from this parenthetical explanation, we must now especially
note two leading truths brought out by the foregoing exposition: the one
concerning the ultimate, or rather the penultimate, state of motion
which the processes described tend to bring about; the other concerning
the concomitant distribution of matter.       This penultimate state of
motion is the moving equilibrium; which, as we have seen, tends to arise
in an aggregate having compound motions, as a transitional state on the
way towards complete equilibrium. Throughout Evolution of all kinds,
there is a continual approximation to, and more or less complete
maintenance of, this moving equilibrium. As in the Solar System there
has been established an independent moving equilibrium�an equilibrium
such that the relative motions of the constituent parts are continually
so counter-balanced by opposite motions, that the mean state of the
whole aggregate never varies; so is it, though in a less distinct
manner, with each form of dependent moving equilibrium. The state of
things exhibited in the cycles of terrestrial changes, in the balanced
functions of organic bodies that have reached their adult forms, and in
the acting and re-acting processes of fully-developed societies, is
similarly one characterized by compensating oscillations. The involved
combination of rhythms seen in each of these cases, has an average
condition which remains practically constant during the deviations ever
taking place on opposite sides of it. And the fact which we have here
particularly to observe, is, that as a corollary from the general law of
equilibration above set forth, the evolution of every aggregate must go
on until this _equilibrium mobile_ is established; since, as we have
seen, an excess of force which the aggregate possesses in any direction,
must eventually be expended in overcoming resistances to change in that
direction: leaving behind only those movements which compensate each
other, and so form a moving equilibrium.       Respecting the structural
state simultaneously reached, it must obviously be one presenting an
arrangement of forces that counterbalance all the forces to which the
aggregate is subject. So long as there remains a residual force in any
direction�be it excess of a force exercised by the aggregate on its
environment, or of a force exercised by its environment on the
aggregate, equilibrium does not exist; and therefore the re-distribution
of matter must continue. Whence it follows that the limit of
heterogeneity towards which every aggregate progresses, is the formation
of as many specializations and combinations of parts, as there are
specialized and combined forces to be met.

                  *       *       *       *       *

§ 131. Those successively changed forms which, if the nebular hypothesis
be granted, must have arisen during the evolution of the Solar System,
were so many transitional kinds of moving equilibrium; severally giving
place to more permanent kinds on the way towards complete equilibration.
Thus the assumption of an oblate spheroidal figure by condensing
nebulous matter, was the assumption of a temporary and partial moving
equilibrium among the component parts�a moving equilibrium that must
have slowly grown more settled, as local conflicting movements were
dissipated.       In the formation and detachment of the nebulous rings,
which, according to this hypothesis, from time to time took place, we
have instances of progressive equilibration ending in the establishment
of a complete moving equilibrium. For the genesis of each such ring,
implies a perfect balancing of that aggregative force which the whole
spheroid exercises on its equatorial portion, by that centrifugal force
which the equatorial portion has acquired during previous concentration:
so long as these two forces are not equal, the equatorial portion
follows the contracting mass; but as soon as the second force has
increased up to an equality with the first, the equatorial portion can
follow no further, and remains behind. While, however, the resulting
ring, regarded as a whole connected by forces with external wholes, has
reached a state of moving equilibrium; its parts are not balanced with
respect to each other. As we before saw (§ 110) the probabilities
against the maintenance of an annular form by nebulous matter, are
immense: from the instability of the homogeneous, it is inferrable that
nebulous matter so distributed must break up into portions; and
eventually concentrate into a single mass. That is to say, the ring must
progress towards a moving equilibrium of a more complete kind, during
the dissipation of that motion which maintained its particles in a
diffused form: leaving at length a planetary body, attended perhaps by a
group of minor bodies, severally having residuary relative motions that
are no longer resisted by sensible media; and there is thus constituted
an _equilibrium mobile_ that is all but absolutely perfect.[18]

Hypothesis aside, the principle of equilibration is still perpetually
illustrated in those minor changes of state which the Solar System is
undergoing. Each planet, satellite, and comet, exhibits to us at its
aphelion a momentary equilibrium between that force which urges it
further away from its primary, and that force which retards its retreat;
since the retreat goes on until the last of these forces exactly
counterpoises the first. In like manner at perihelion a converse
equilibrium is momentarily established. The variation of each orbit in
size, in eccentricity, and in the position of its plane, has similarly a
limit at which the forces producing change in the one direction, are
equalled by those antagonizing it; and an opposite limit at which an
opposite arrest takes place. Meanwhile, each of these simple
perturbations, as well as each of the complex ones resulting from their
combination, exhibits, besides the temporary equilibration at each of
its extremes, a certain general equilibration of compensating deviations
on either side of a mean state.       That the moving equilibrium thus
constituted, tends, in the course of indefinite time, to lapse into a
complete equilibrium, by the gradual decrease of planetary motions and
eventually integration of all the separate masses composing the Solar
System, is a belief suggested by certain observed cometary retardations,
and entertained by some of high authority. The received opinion that the
appreciable diminution in the period of Encke�s comet, implies a loss of
momentum caused by resistance of the ethereal medium, commits
astronomers who hold it, to the conclusion that this same resistance
must cause a loss of planetary motions�a loss which, infinitesimal
though it may be in such periods as we can measure, will, if
indefinitely continued, bring these motions to a close. Even should
there be, as Sir John Herschel suggests, a rotation of the ethereal
medium in the same direction with the planets, this arrest, though
immensely postponed, would not be absolutely prevented. Such an
eventuality, however, must in any case be so inconceivably remote as to
have no other than a speculative interest for us. It is referred to
here, simply as illustrating the still-continued tendency towards
complete equilibrium, through the still-continued dissipation of
sensible motion, or transformation of it into insensible motion.

But there is another species of equilibration going on in the Solar
System, with which we are more nearly concerned�the equilibration of
that molecular motion known as heat. The tacit assumption hitherto
current, that the Sun can continue to give off an undiminished amount of
light and heat through all future time, is fast being abandoned.
Involving as it does, under a disguise, the conception of power produced
out of nothing, it is of the same order as the belief that misleads
perpetual-motion schemers. The spreading recognition of the truth that
force is persistent, and that consequently whatever force is manifested
under one shape must previously have existed under another shape, is
carrying with it a recognition of the truth that the force known to us
in solar radiations, is the changed form of some other force of which
the Sun is the seat; and that by the gradual dissipation of these
radiations into space, this other force is being slowly exhausted. The
aggregative force by which the Sun�s substance is drawn to his centre of
gravity, is the only one which established physical laws warrant us in
suspecting to be the correlate of the forces thus emanating from him:
the only source of a known kind that can be assigned for the insensible
motions constituting solar light and heat, is the sensible motion which
disappears during the progressing concentration of the Sun�s substance.
We before saw it to be a corollary from the nebular hypothesis, that
there is such a progressing concentration of the Sun�s substance. And
here remains to be added the further corollary, that just as in the case
of the smaller members of the Solar System, the heat generated by
concentration, long ago in great part radiated into space, has left only
a central residue that now escapes but slowly; so in the case of that
immensely larger mass forming the Sun, the immensely greater quantity of
heat generated and still in process of rapid diffusion, must, as the
concentration approaches its limit, diminish in amount, and eventually
leave only an inappreciable internal remnant.       With or without the
accompaniment of that hypothesis of nebular condensation, whence, as we
see, it naturally follows, the doctrine that the Sun is gradually losing
his heat, has now gained considerable currency; and calculations have
been made, both respecting the amount of heat and light already
radiated, as compared with the amount that remains, and respecting the
period during which active radiation is likely to continue. Prof.
Helmholtz estimates, that since the time when, according to the nebular
hypothesis, the matter composing the Solar System extended to the orbit
of Neptune, there has been evolved by the arrest of sensible motion, an
amount of heat 454 times as great as that which the Sun still has to
give out. He also makes an approximate estimate of the rate at which
this remaining 1/454th is being diffused: showing that a diminution of
the Sun�s diameter to the extent of 1/10,000, would produce heat, at the
present rate, for more than 2000 years; or in other words, that a
contraction of 1/20,000,000 of his diameter, suffices to generate the
amount of light and heat annually emitted; and that thus, at the present
rate of expenditure, the Sun�s diameter will diminish by something like
1/20 in the lapse of the next million years.[19] Of course these
conclusions are not to be considered as more than rude approximations to
the truth. Until quite recently, we have been totally ignorant of the
Sun�s chemical composition; and even now have obtained but a superficial
knowledge of it. We know nothing of his internal structure; and it is
quite possible (probable, I believe,) that the assumptions respecting
central density, made in the foregoing estimates, are wrong. But no
uncertainty in the data on which these calculations proceed, and no
consequent error in the inferred rate at which the Sun is expending his
reserve of force, militates against the general proposition that this
reserve of force _is_ being expended; and must in time be exhausted.
Though the residue of undiffused motion in the Sun, may be much greater
than is above concluded; though the rate of radiation cannot, as
assumed, continue at a uniform rate, but must eventually go on with
slowly-decreasing rapidity; and though the period at which the Sun will
cease to afford us adequate light and heat, is very possibly far more
distant than above implied; yet such a period must some time be reached,
and this is all which it here concerns us to observe.

Thus while the Solar System, if evolved from diffused matter, has
illustrated the law of equilibration in the establishment of a complete
moving equilibrium; and while, as at present constituted, it illustrates
the law of equilibration in the balancing of all its movements; it also
illustrates this law in the processes which astronomers and physicists
infer are still going on. That motion of masses produced during
Evolution, is being slowly re-diffused in molecular motion of the
ethereal medium; both through the progressive integration of each mass,
and the resistance to its motion through space. Infinitely remote as may
be the state when all the motions of masses shall be transformed into
molecular motion, and all the molecular motion equilibrated; yet such a
state of complete integration and complete equilibration, is that
towards which the changes now going on throughout the Solar System
inevitably tend.

                  *       *       *       *       *

§ 132. A spherical figure is the one which can alone equilibrate the
forces of mutually-gravitating atoms. If the aggregate of such atoms has
a rotatory motion, the form of equilibrium becomes a spheroid of greater
or less oblateness, according to the rate of rotation; and it has been
ascertained that the Earth is an oblate spheroid, diverging just as much
from sphericity as is requisite to counterbalance the centrifugal force
consequent on its velocity round its axis. That is to say, during the
evolution of the Earth, there has been reached a complete equilibrium of
those forces which affect its general outline.       The only other
process of equilibration which the Earth as a whole can exhibit, is the
loss of its axial motion; and that any such loss is going on, we have no
direct evidence. It has been contended, however, by Prof. Helmholtz,
that inappreciable as may be its effect within known periods of time,
the friction of the tidal wave must be slowly diminishing the Earth�s
rotatory motion, and must eventually destroy it. Now though it seems an
oversight to say that the Earth�s rotation can thus be destroyed, since
the extreme effect, to be reached only in infinite time by such a
process, would be an extension of the Earth�s day to the length of a
lunation; yet it seems clear that this friction of the tidal wave is a
real cause of decreasing rotation. Slow as its action is, we must
recognize it as exemplifying, under another form, the universal progress
towards equilibrium.

It is needless to point out, in detail, how those movements which the
Sun�s rays generate in the air and water on the Earth�s surface, and
through them in the Earth�s solid substance,[20] one and all teach the
same general truth. Evidently the winds and waves and streams, as well
as the denudations and depositions they effect, perpetually illustrate
on a grand scale, and in endless modes, that gradual dissipation of
motions described in the first section; and the consequent tendency
towards a balanced distribution of forces. Each of these sensible
motions, produced directly or indirectly by integration of those
insensible motions communicated from the Sun, becomes, as we have seen,
divided and subdivided into motions less and less sensible; until it is
finally reduced to insensible motions, and radiated from the Earth in
the shape of thermal undulations.       In their totality, these complex
movements of aerial, liquid, and solid matter on the Earth�s crust,
constitute a dependent moving equilibrium. As we before saw, there is
traceable throughout them an involved combination of rhythms. The
unceasing circulation of water from the ocean to the land, and from the
land back to the ocean, is a type of these various compensating actions;
which, in the midst of all the irregularities produced by their mutual
interferences, maintain an average. And in this, as in other
equilibrations of the third order, we see that the power from moment to
moment in course of dissipation, is from moment to moment renewed from
without: the rises and falls in the supply, being balanced by rises and
falls in the expenditure; as witness the correspondence between the
magnetic variations and the cycle of the solar spots.       But the fact
it chiefly concerns us to observe, is, that this process must go on
bringing things ever nearer to complete rest. These mechanical
movements, meteorologic and geologic, which are continually being
equilibrated, both temporarily by counter-movements and permanently by
the dissipation of such movements and counter-movements, will slowly
diminish as the quantity of force received from the Sun diminishes. As
the insensible motions propagated to us from the centre of our system
become feebler, the sensible motions here produced by them must
decrease; and at that remote period when the solar heat has ceased to be
appreciable, there will no longer be any appreciable re-distributions of
matter on the surface of our planet.

Thus from the highest point of view, all terrestrial changes are
incidents in the course of cosmical equilibration. It was before pointed
out, (§ 80) that of the incessant alterations which the Earth�s crust
and atmosphere undergo, those which are not due to the still-progressing
motion of the Earth�s substance towards its centre of gravity, are due
to the still-progressing motion of the Sun�s substance towards its
centre of gravity. Here it is to be remarked, that this continuance of
integration in the Earth and in the Sun, is a continuance of that
transformation of sensible motion into insensible motion which we have
seen ends in equilibration; and that the arrival in each case at the
extreme of integration, is the arrival at a state in which no more
sensible motion remains to be transformed into insensible motion�a state
in which the forces producing integration and the forces opposing
integration, have become equal.

                  *       *       *       *       *

§ 133. Every living body exhibits, in a four-fold form, the process we
are tracing out�exhibits it from moment to moment in the balancing of
mechanical forces; from hour to hour in the balancing of functions; from
year to year in the changes of state that compensate changes of
condition; and finally in the complete arrest of vital movements at
death. Let us consider the facts under these heads.

The sensible motion constituting each visible action of an organism, is
soon brought to a close by some adverse force within or without the
organism. When the arm is raised, the motion given to it is antagonized
partly by gravity and partly by the internal resistances consequent on
structure; and its motion, thus suffering continual deduction, ends when
the arm has reached a position at which the forces are equilibrated. The
limits of each systole and diastole of the heart, severally show us a
momentary equilibrium between muscular strains that produce opposite
movements; and each gush of blood requires to be immediately followed by
another, because the rapid dissipation of its momentum would otherwise
soon bring the mass of circulating fluid to a stand. As much in the
actions and re-actions going on among the internal organs, as in the
mechanical balancing of the whole body, there is at every instant a
progressive equilibration of the motions at every instant produced.
      Viewed in their aggregate, and as forming a series, the organic
functions constitute a dependent moving equilibrium�a moving
equilibrium, of which the motive power is ever being dissipated through
the special equilibrations just exemplified, and is ever being renewed
by the taking in of additional motive power. Food is a store of force
which continually adds to the momentum of the vital actions, as much as
is continually deducted from them by the forces overcome. All the
functional movements thus maintained, are, as we have seen, rhythmical
(§ 96); by their union compound rhythms of various lengths and
complexities are produced; and in these simple and compound rhythms, the
process of equilibration, besides being exemplified at each extreme of
every rhythm, is seen in the habitual preservation of a constant mean,
and in the re-establishment of that mean when accidental causes have
produced divergence from it. When, for instance, there is a great
expenditure of motion through muscular activity, there arises a
re-active demand on those stores of latent motion which are laid up in
the form of consumable matter throughout the tissues: increased
respiration and increased rapidity of circulation, are instrumental to
an extra genesis of force, that counter-balances the extra dissipation
of force. This unusual transformation of molecular motion into sensible
motion, is presently followed by an unusual absorption of food�the
source of molecular motion; and in proportion as there has been a
prolonged draft upon the spare capital of the system, is there a
tendency to a prolonged rest, during which that spare capital is
replaced. If the deviation from the ordinary course of the functions has
been so great as to derange them, as when violent exertion produces loss
of appetite and loss of sleep, an equilibration is still eventually
effected. Providing the disturbance is not such as to overturn the
balance of the functions, and destroy life (in which case a complete
equilibration is suddenly effected), the ordinary balance is by and by
re-established: the returning appetite is keen in proportion as the
waste has been large; while sleep, sound and prolonged, makes up for
previous wakefulness. Not even in those extreme cases where some excess
has wrought a derangement that is never wholly rectified, is there an
exception to the general law; for in such cases the cycle of the
functions is, after a time, equilibrated about a new mean state, which
thenceforth becomes the normal state of the individual. Thus, among the
involved rhythmical changes constituting organic life, any disturbing
force that works an excess of change in some direction, is gradually
diminished and finally neutralized by antagonistic forces; which
thereupon work a compensating change in the opposite direction, and so,
after more or less of oscillation, restore the medium condition. And
this process it is, which constitutes what physicians call the _vis
medicatrix naturæ_.       The third form of equilibration displayed by
organic bodies, is a necessary sequence of that just illustrated. When
through a change of habit or circumstance, an organism is permanently
subject to some new influence, or different amount of an old influence,
there arises, after more or less disturbance of the organic rhythms, a
balancing of them around the new average condition produced by this
additional influence. As temporary divergences of the organic rhythms
are counteracted by temporary divergences of a reverse kind; so there is
an equilibration of their permanent divergences by the genesis of
opposing divergences that are equally permanent. If the quantity of
motion to be habitually generated by a muscle, becomes greater than
before, its nutrition becomes greater than before. If the expenditure of
the muscle bears to its nutrition, a greater ratio than expenditure
bears to nutrition in other parts of the system; the excess of nutrition
becomes such that the muscle grows. And the cessation of its growth is
the establishment of a balance between the daily waste and the daily
repair�the daily expenditure of force, and the amount of latent force
daily added. The like must manifestly be the case with all organic
modifications consequent on change of climate or food. This is a
conclusion which we may safely draw without knowing the special
re-arrangements that effect the equilibration. If we see that a
different mode of life is followed, after a period of functional
derangement, by some altered condition of the system�if we see that this
altered condition, becoming by and by established, continues without
further change; we have no alternative but to say, that the new forces
brought to bear on the system, have been compensated by the opposing
forces they have evoked. And this is the interpretation of the process
which we call _adaptation_.       Finally, each organism illustrates the
law in the _ensemble_ of its life. At the outset it daily absorbs under
the form of food, an amount of force greater than it daily expends; and
the surplus is daily equilibrated by growth. As maturity is approached,
this surplus diminishes; and in the perfect organism, the day�s
absorption of potential motion balances the day�s expenditure of actual
motion. That is to say, during adult life, there is continuously
exhibited an equilibration of the third order. Eventually, the daily
loss, beginning to out-balance the daily gain, there results a
diminishing amount of functional action; the organic rhythms extend less
and less widely on each side of the medium state; and there finally
results that complete equilibration which we call death.

The ultimate structural state accompanying that ultimate functional
state towards which an organism tends, both individually and as a
species, may be deduced from one of the propositions set down in the
opening section of this chapter. We saw that the limit of heterogeneity
is arrived at whenever the equilibration of any aggregate becomes
complete�that the re-distribution of matter can continue so long only as
there continues any motion unbalanced. Whence we found it to follow that
the final structural arrangements, must be such as will meet all the
forces acting on the aggregate, by equivalent antagonist forces. What is
the implication in the case of organic aggregates; the equilibrium of
which is a moving one? We have seen that the maintenance of such a
moving equilibrium, requires the habitual genesis of internal forces
corresponding in number, directions, and amounts to the external
incident forces�as many inner functions, single or combined, as there
are single or combined outer actions to be met. But functions are the
correlatives of organs; amounts of functions are, other things equal,
the correlatives of sizes of organs; and combinations of functions the
correlatives of connections of organs. Hence the structural complexity
accompanying functional equilibration, is definable as one in which
there are as many specialized parts as are capable, separately and
jointly, of counteracting the separate and joint forces amid which the
organism exists. And this is the limit of organic heterogeneity; to
which man has approached more nearly than any other creature.

Groups of organisms display this universal tendency towards a balance
very obviously. In § 96, every species of plant and animal was shown to
be perpetually undergoing a rhythmical variation in number�now from
abundance of food and absence of enemies rising above its average; and
then by a consequent scarcity of food and abundance of enemies being
depressed below its average. And here we have to observe that there is
thus maintained an equilibrium between the sum of those forces which
result in the increase of each race, and the sum of those forces which
result in its decrease. Either limit of variation is a point at which
the one set of forces, before in excess of the other, is counterbalanced
by it. And amid these oscillations produced by their conflict, lies that
average number of the species at which its expansive tendency is in
equilibrium with surrounding repressive tendencies. Nor can it be
questioned that this balancing of the preservative and destructive
forces which we see going on in every race, must necessarily go on.
Since increase of number cannot but continue until increase of mortality
stops it; and decrease of number cannot but continue until it is either
arrested by fertility or extinguishes the race entirely.

                  *       *       *       *       *

§ 134. The equilibrations of those nervous actions which constitute what
we know as mental life, may be classified in like manner with those
which constitute what we distinguish as bodily life. We may deal with
them in the same order.

Each pulse of nervous force from moment to moment generated, (and it was
shown in § 97 that nervous currents are not continuous but rhythmical)
is met by counteracting forces; in overcoming which it is dispersed and
equilibrated. When tracing out the correlation and equivalence of
forces, we saw that each sensation and emotion, or rather such part of
it as remains after the excitation of associated ideas and feelings, is
expended in working bodily changes�contractions of the involuntary
muscles, the voluntary muscles, or both; as also in a certain
stimulation of secreting organs. That the movements thus initiated are
ever being brought to a close by the opposing forces they evoke, was
pointed out above; and here it is to be observed that the like holds
with the nervous changes thus initiated. Various facts prove that the
arousing of a thought or feeling, always involves the overcoming of a
certain resistance: instance the fact that where the association of
mental states has not been frequent, a sensible effort is needed to call
up the one after the other; instance the fact that during nervous
prostration there is a comparative inability to think�the ideas will not
follow one another with the habitual rapidity; instance the converse
fact that at times of unusual energy, natural or artificial, the
friction of thought becomes relatively small, and more numerous, more
remote, or more difficult connections of ideas are formed. That is to
say, the wave of nervous energy each instant generated, propagates
itself throughout body and brain, along those channels which the
conditions at the instant render lines of least resistance; and
spreading widely in proportion to its amount, ends only when it is
equilibrated by the resistances it everywhere meets.       If we
contemplate mental actions us extending over hours and days, we discover
equilibrations analogous to those hourly and daily established among the
bodily functions. In the one case as in the other, there are rhythms
which exhibit a balancing of opposing forces at each extreme, and the
maintenance of a certain general balance. This is seen in the daily
alternation of mental activity and mental rest�the forces expended
during the one being compensated by the forces acquired during the
other. It is also seen in the recurring rise and fall of each desire:
each desire reaching a certain intensity, is equilibrated either by
expenditure of the force it embodies, in the desired actions, or, less
completely, in the imagination of such actions: the process ending in
that satiety, or that comparative quiescence, forming the opposite limit
of the rhythm. And it is further manifest under a two-fold form, on
occasions of intense joy or grief: each paroxysm of passion, expressing
itself in vehement bodily actions, presently reaches an extreme whence
the counteracting forces produce a return to a condition of moderate
excitement; and the successive paroxysms finally diminishing in
intensity, end in a mental equilibrium either like that before existing,
or partially differing from it in its medium state.       But the
species of mental equilibration to be more especially noted, is that
shown in the establishment of a correspondence between relations among
our states of consciousness and relations in the external world. Each
outer connection of phenomena which we are capable of perceiving,
generates, through accumulated experiences, an inner connection of
mental states; and the result towards which this process tends, is the
formation of a mental connection having a relative strength that answers
to the relative constancy of the physical connection represented. In
conformity with the general law that motion pursues the line of least
resistance, and that, other things equal, a line once taken by motion is
made a line that will be more readily pursued by future motion; we have
seen that the ease with which nervous impressions follow one another,
is, other things equal, great in proportion to the number of times they
have been repeated together in experience. Hence, corresponding to such
an invariable relation as that between the resistance of an object and
some extension possessed by it, there arises an indissoluble connection
in consciousness; and this connection, being as absolute internally as
the answering one is externally, undergoes no further change�the inner
relation is in perfect equilibrium with the outer relation. Conversely,
it hence happens that to such uncertain relations of phenomena as that
between clouds and rain, there arise relations of ideas of a like
uncertainty; and if, under given aspects of the sky, the tendencies to
infer fair or foul weather, correspond to the frequencies with which
fair or foul weather follow such aspects, the accumulation of
experiences has balanced the mental sequences and the physical
sequences. When it is remembered that between these extremes there are
countless orders of external connections having different degrees of
constancy, and that during the evolution of intelligence there arise
answering internal associations having different degrees of cohesion; it
will be seen that there is a progress towards equilibrium between the
relations of thought and the relations of things. This equilibration can
end only when each relation of things has generated in us a relation of
thought, such that on the occurrence of the conditions, the relation in
thought arises as certainly as the relation in things. Supposing this
state to be reached (which however it can be only in infinite time)
experience will cease to produce any further mental evolution�there will
have been reached a perfect correspondence between ideas and facts; and
the intellectual adaptation of man to his circumstances will be
complete.       The like general truths are exhibited in the process
moral of adaptation; which is a continual approach to equilibrium
between the emotions and the kinds of conduct necessitated by
surrounding conditions. The connections of feelings and actions, are
determined in the same way as the connections of ideas: just as
repeating the association of two ideas, facilitates the excitement of
the one by the other; so does each discharge of feeling into action,
render the subsequent discharge of such feeling into such action more
easy. Hence it happens that if an individual is placed permanently in
conditions which demand more action of a special kind than has before
been requisite, or than is natural to him�if the pressure of the painful
feelings which these conditions entail when disregarded, impels him to
perform this action to a greater extent�if by every more frequent or
more lengthened performance of it under such pressure, the resistance is
somewhat diminished; then, clearly, there is an advance towards a
balance between the demand for this kind of action and the supply of it.
Either in himself, or in his descendants continuing to live under these
conditions, enforced repetition must eventually bring about a state in
which this mode of directing the energies will be no more repugnant than
the various other modes previously natural to the race. Hence the limit
towards which emotional modification perpetually tends, and to which it
must approach indefinitely near (though it can absolutely reach it only
in infinite time) is a combination of desires that correspond to all the
different orders of activity which the circumstances of life call
for�desires severally proportionate in strength to the needs for these
orders of activity; and severally satisfied by these orders of activity.
In what we distinguish as acquired habits, and in the moral differences
of races and nations produced by habits that are maintained through
successive generations, we have countless illustrations of this
progressive adaptation; which can cease only with the establishment of a
complete equilibrium between constitution and conditions.

Possibly some will fail to see how the equilibrations described in this
section, can be classed with those preceding them; and will be inclined
to say that what are here set down as facts, are but analogies.
Nevertheless such equilibrations are as truly physical as the rest. To
show this fully, would require a more detailed analysis than can now be
entered on. For the present it must suffice to point out, as before (§
82), that what we know subjectively as states of consciousness, are,
objectively, modes of force; that so much feeling is the correlate of so
much motion; that the performance of any bodily action is the
transformation of a certain amount of feeling into its equivalent amount
of motion; that this bodily action is met by forces which it is expended
in overcoming; and that the necessity for the frequent repetition of
this action, implies the frequent recurrence of forces to be so
overcome. Hence the existence in any individual of an emotional stimulus
that is in equilibrium with certain external requirements, is literally
the habitual production of a certain specialized portion of nervous
energy, equivalent in amount to a certain order of external resistances
that are habitually met. And thus the ultimate state, forming the limit
towards which Evolution carries us, is one in which the kinds and
quantities of mental energy daily generated and transformed into
motions, are equivalent to, or in equilibrium with, the various orders
and degrees of surrounding forces which antagonize such motions.

                  *       *       *       *       *

§ 135. Each society taken as a whole, displays the process of
equilibration in the continuous adjustment of its population to its
means of subsistence. A tribe of men living on wild animals and fruits,
is manifestly, like every tribe of inferior creatures, always
oscillating about that average number which the locality can support.
Though by artificial production, and by successive improvements in
artificial production, a superior race continually alters the limit
which external conditions put to population; yet there is ever a
checking of population at the temporary limit reached. It is true that
where the limit is being so rapidly changed as among ourselves, there is
no actual stoppage: there is only a rhythmical variation in the rate of
increase. But in noting the causes of this rhythmical variation�in
watching how, during periods of abundance, the proportion of marriages
increases, and how it decreases during periods of scarcity; it will be
seen that the expansive force produces unusual advance whenever the
repressive force diminishes, and _vice versâ_; and thus there is as near
a balancing of the two as the changing conditions permit.

The internal actions constituting social functions, exemplify the
general principle no less clearly. Supply and demand are continually
being adjusted throughout all industrial processes; and this
equilibration is interpretable in the same way as preceding ones. The
production and distribution of a commodity, is the expression of a
certain aggregate of forces causing special kinds and amounts of motion.
The price of this commodity, is the measure of a certain other aggregate
of forces expended by the labourer who purchases it, in other kinds and
amounts of motion. And the variations of price represent a rhythmical
balancing of these forces. Every rise or fall in the rate of interest,
or change in the value of a particular security, implies a conflict of
forces in which some, becoming temporarily predominant, cause a movement
that is presently arrested or equilibrated by the increase of opposing
forces; and amid these daily and hourly oscillations, lies a more
slowly-varying medium, into which the value ever tends to settle; and
would settle but for the constant addition of new influences.       As
in the individual organism so in the social organism, functional
equilibrations generate structural equilibrations. When on the workers
in any trade there comes an increased demand, and when in return for the
increased supply, there is given to them an amount of other commodities
larger than was before habitual�when, consequently, the resistances
overcome by them in sustaining life are less than the resistances
overcome by other workers; there results a flow of other workers into
this trade. This flow continues until the extra demand is met, and the
wages so far fall again, that the total resistance overcome in obtaining
a given amount of produce, is as great in this newly-adopted occupation
as in the occupations whence it drew recruits. The occurrence of motion
along lines of least resistance, was before shown to necessitate the
growth of population in those places where the labour required for
self-maintenance is the smallest; and here we further see that those
engaged in any such advantageous locality, or advantageous business,
must multiply till there arises an approximate balance between this
locality or business and others accessible to the same citizens. In
determining the career of every youth, we see an estimation by parents
of the respective advantages offered by all that are available, and a
choice of the one which promises best; and through the consequent influx
into trades that are at the time most profitable, and the withholding of
recruits from over-stocked trades, there is insured a general equipoise
between the power of each social organ and the function it has to
perform.

The various industrial actions and re-actions thus continually
alternating, constitute a dependent moving equilibrium like that which
is maintained among the functions of an individual organism. And this
dependent moving equilibrium parallels those already contemplated, in
its tendency to become more complete. During early stages of social
evolution, while yet the resources of the locality inhabited are
unexplored, and the arts of production undeveloped, there is never
anything more than a temporary and partial balancing of such actions,
under the form of acceleration or retardation of growth. But when a
society approaches the maturity of that type on which it is organized,
the various industrial activities settle down into a comparatively
constant state. Moreover, it is observable that advance in organization,
as well as advance in growth, is conducive to a better equilibrium of
industrial functions. While the diffusion of mercantile information is
slow, and the means of transport deficient, the adjustment of supply to
demand is extremely imperfect: great over-production of each commodity
followed by great under-production, constitute a rhythm having extremes
that depart very widely from the mean state in which demand and supply
are equilibrated. But when good roads are made, and there is a rapid
diffusion of printed or written intelligence, and still more when
railways and telegraphs come into existence�when the periodical fairs of
early days lapse into weekly markets, and these into daily markets;
there is gradually produced a better balance of production and
consumption. Extra demand is much more quickly followed by augmented
supply; and the rapid oscillations of price within narrow limits on
either side of a comparatively uniform mean, indicate a near approach to
equilibrium.       Evidently this industrial progress has for its limit,
that which Mr. Mill has called �the stationary state.� When population
shall have become dense over all habitable parts of the globe; when the
resources of every region have been fully explored; and when the
productive arts admit of no further improvements; there must result an
almost complete balance, both between the fertility and mortality of
each society, and between its producing and consuming activities. Each
society will exhibit only minor deviations from its average number, and
the rhythm of its industrial functions will go on from day to day and
year to year with comparatively insignificant perturbations. This limit,
however, though we are inevitably advancing towards it, is indefinitely
remote; and can never indeed be absolutely reached. The peopling of the
Earth up to the point supposed, cannot take place by simple spreading.
In the future, as in the past, the process will be carried on
rhythmically, by waves of emigration from new and higher centres of
civilization successively arising; and by the supplanting of inferior
races by the superior races they beget; and the process so carried on
must be extremely slow. Nor does it seem to me that such an
equilibration will, as Mr. Mill suggests, leave scope for further mental
culture and moral progress; but rather that the approximation to it must
be simultaneous with the approximation to complete equilibrium between
man�s nature and the conditions of his existence.

One other kind of social equilibration has still to be considered:�that
which results in the establishment of governmental institutions, and
which becomes complete as these institutions fall into harmony with the
desires of the people. There is a demand and supply in political affairs
as in industrial affairs; and in the one case as in the other, the
antagonist forces produce a rhythm which, at first extreme in its
oscillations, slowly settles down into a moving equilibrium of
comparative regularity. Those aggressive impulses inherited from the
pre-social state�those tendencies to seek self-satisfaction regardless
of injury to other beings, which are essential to a predatory life,
constitute an anti-social force, tending ever to cause conflict and
eventual separation of citizens. Contrariwise, those desires whose ends
can be achieved only by union, as well as those sentiments which find
satisfaction through intercourse with fellow-men, and those resulting in
what we call loyalty, are forces tending to keep the units of a society
together. On the one hand, there is in each citizen, more or less of
resistance against all restraints imposed on his actions by other
citizens: a resistance which, tending continually to widen each
individual�s sphere of action, and reciprocally to limit the spheres of
action of other individuals, constitutes a repulsive force mutually
exercised by the members of a social aggregate. On the other hand, the
general sympathy of man for man, and the more special sympathy of each
variety of man for others of the same variety, together with sundry
allied feelings which the social state gratifies, act as an attractive
force, tending ever to keep united those who have a common ancestry. And
since the resistances to be overcome in satisfying the totality of their
desires when living separately, are greater than the resistances to be
overcome in satisfying the totality of their desires when living
together, there is a residuary force that prevents their separation.
Like all other opposing forces, those exerted by citizens on each other,
are ever producing alternating movements, which, at first extreme,
undergo a gradual diminution on the way to ultimate equilibrium. In
small, undeveloped societies, marked rhythms result from these
conflicting tendencies. A tribe whose members have held together for a
generation or two, reaches a size at which it will not hold together;
and on the occurrence of some event causing unusual antagonism among its
members, divides. Each primitive nation, depending largely for its
continued union on the character of its chief, exhibits wide
oscillations between an extreme in which the subjects are under rigid
restraint, and an extreme in which the restraint is not enough to
prevent disorder. In more advanced nations of like type, we always find
violent actions and reactions of the same essential nature��despotism
tempered by assassination,� characterizing a political state in which
unbearable repression from time to time brings about a bursting of all
bonds. In this familiar fact, that a period of tyranny is followed by a
period of license and _vice versâ_, we see how these opposing forces are
ever equilibrating each other; and we also see, in the tendency of such
movements and counter-movements to become more moderate, how the
equilibration progresses towards completeness. The conflicts between
Conservatism (which stands for the restraints of society over the
individual) and Reform (which stands for the liberty of the individual
against society), fall within slowly approximating limits; so that the
temporary predominance of either, produces a less marked deviation from
the medium state.       This process, now so far advanced among
ourselves that the oscillations are comparatively unobtrusive, must go
on till the balance between the antagonist forces approaches
indefinitely near perfection. For, as we have already seen, the
adaptation of man�s nature to the conditions of his existence, cannot
cease until the internal forces which we know as feelings are in
equilibrium with the external forces they encounter. And the
establishment of this equilibrium, is the arrival at a state of human
nature and social organization, such that the individual has no desires
but those which may be satisfied without exceeding his proper sphere of
action, while society maintains no restraints but those which the
individual voluntarily respects. The progressive extension of the
liberty of citizens, and the reciprocal removal of political
restrictions, are the steps by which we advance towards this state. And
the ultimate abolition of all limits to the freedom of each, save those
imposed by the like freedom of all, must result from the complete
equilibration between man�s desires and the conduct necessitated by
surrounding conditions.

Of course in this case, as in the preceding ones, there is thus involved
a limit to the increase of heterogeneity. A few pages back, we reached
the conclusion that each advance in mental evolution, is the
establishment of some further internal action, corresponding to some
further external action�some additional connection of ideas or feelings,
answering to some before unknown or unantagonized connection of
phenomena. We inferred that each such new function, involving some new
modification of structure, implies an increase of heterogeneity; and
that thus, increase of heterogeneity must go on, while there remain any
outer relations affecting the organism which are unbalanced by inner
relations. Whence we saw it to follow that increase of heterogeneity can
come to an end only as equilibration is completed. Evidently the like
must simultaneously take place with society. Each increment of
heterogeneity in the individual, must directly or indirectly involve, as
cause or consequence, some increment of heterogeneity in the
arrangements of the aggregate of individuals. And the limit to social
complexity can be arrived at, only with the establishment of the
equilibrium, just described, between social and individual forces.

                  *       *       *       *       *

§ 136. Here presents itself a final question, which has probably been
taking a more or less distinct shape in the minds of many, while reading
this chapter. �If Evolution of every kind, is an increase in complexity
of structure and function that is incidental to the universal process of
equilibration�if equilibration, passing through the gradually-perfected
forms of moving equilibrium, must end in complete rest; what is the fate
towards which all things tend? If the bodies constituting our Solar
System are slowly dissipating the forces they possess�if the Sun is
losing his heat at a rate which, though insignificant as stated in terms
of our chronology, will tell in millions of years�if geologic and
meteorologic processes cannot but diminish in activity as the Sun�s
radiations diminish�if with the diminution of these radiations there
must also go on a diminution in the quantity of vegetal and animal
existence�if Man and Society, however high the degree of evolution at
which they arrive, are similarly dependent on this supply of force that
is gradually coming to an end�if thus the highest, equally with the
lowest, terrestrial life, must eventually dwindle and disappear; are we
not manifestly progressing towards omnipresent death? And have we thus
to contemplate, as the out-come of things, a universe of extinct suns
round which circle planets devoid of life?�

That such a state must be the proximate end of the processes everywhere
going on, seems beyond doubt. But the further question tacitly involved,
whether this state will continue eternally, is quite a different one. To
give a positive answer to this further question would be quite
illegitimate; since to affirm any proposition into which unlimited time
enters as one of the terms, is to affirm a proposition of which one term
cannot be represented in consciousness�is to affirm an unthinkable
proposition. At a first glance it may appear that the reverse conclusion
must be equally illegitimate; and that so the question is altogether
insoluble. But further consideration will show that this is not true. So
long as the terms to which we confine our reasonings are finite, the
finite conclusions reached are not necessarily illegitimate. Though, if
the general argument, when carried out, left no apparent escape from the
inference that the state of rest to which Evolution is carrying things,
must, when arrived at, last for ever, this inference would be invalid,
as transcending the scope of human intelligence; yet if, on pushing
further the general argument, we bring out the inference that such a
state will not last for ever, this inference is not necessarily invalid:
since, by the hypothesis, it contains no terms necessarily transcending
the scope of human intelligence. It is permissible therefore, to
inquire, what are the probable ulterior results of this process which
must bring Evolution to a close in Universal Death. Without being so
rash as to form anything like a positive conclusion on a matter so vast
and so far beyond the boundaries of exact science; we may still inquire
what _seems_ to be the remote future towards which the facts point.

It has been already shown that all equilibration, so far as we can trace
it, is relative. The dissipation of a body�s motion by communication of
it to surrounding matter, solid, liquid, gaseous, and ethereal, tends to
bring the body to a fixed position in relation to the matter that
abstracts its motion. But all its other motions continue as before. The
arrest of a cannon-shot does not diminish its movement towards the East
at a thousand miles an hour, along with the wall it has struck; and a
gradual dispersion of the Earth�s rotatory motion, would abstract
nothing from the million and a half miles per day through which the
Earth speeds in its orbit. Further, we have to bear in mind that this
motion, the disappearance of which causes relative equilibration, is not
lost but simply transferred; and by continual division and subdivision
finally reduced to ethereal undulations and radiated through space.
Whether the sensible motion dissipated during relative equilibration, is
directly transformed into insensible motion, as happens in the case of
the Sun; or whether, as in the sensible motions going on around us, it
is directly transformed into smaller sensible motions, and these into
still smaller, until they become insensible, matters not. In every
instance the ultimate result is, that whatever motion of masses is lost,
re-appears as molecular motion pervading space. Thus the questions we
have to consider, are�Whether after the completion of all the relative
equilibrations above contemplated as bringing Evolution to a close,
there remain any further equilibrations to be effected?�Whether there
are any other motions of masses that must eventually be transformed into
molecular motion?�And if there are such other motions, what must be the
consequence when the molecular motion generated by their transformation,
is added to that which already exists?

To the first of these questions the answer is, that there _do_ remain
motions which are undiminished by all the relative equilibrations thus
far considered; namely, the motions of translation possessed by those
vast masses of incandescent matter called stars�masses now known to be
suns that are in all probability, like our own, surrounded by circling
groups of planets. The belief that the stars are literally fixed, has
long since been exploded: observation has proved many of them to have
sensible proper motions. Moreover, it has been ascertained by
measurement, that in relation to the stars nearest to us, our own star
is moving at the rate of about half a million miles per day; and if, as
is admitted to be not improbable by sundry astronomers, our own star is
traversing space in the same direction with adjacent stars, its absolute
velocity may be, and most likely is, immensely greater than this. Now no
such changes as those taking place within the Solar System, even when
carried to the extent of integrating the whole of its matter into one
mass, and diffusing all its relative movements in an insensible form
through space, can affect these sidereal movements. Hence, there appears
no alternative but to infer, that these sidereal movements must remain
to be equilibrated by some subsequent process.

The next question that arises, if we venture to inquire the probable
nature of this process, is�To what law do sidereal motions conform? And
to this question Astronomy replies�the law of gravitation. The relative
motions of binary stars have proved this. When it was discovered that
certain of the double stars are not optically double but physically
double, and move round each other, it was at once suspected that their
revolutions might be regulated by a mutual attraction like that which
regulates the revolutions of planets and satellites. The requisite
measurements having been from time to time made, the periodic times of
sundry binary stars were calculated on this assumption; and the
subsequent performances of their revolutions in the predicted periods,
have completely verified the assumption. If, then, it is demonstrated
that these remote bodies are centres of gravitation�if we infer that all
other stars are centres of gravitation, as we may fairly do�and if we
draw the unavoidable corollary, that this gravitative force which so
conspicuously affects stars that are comparatively near each other, must
affect remote stars; we find ourselves led to the conclusion that all
the members of our Sidereal System gravitate, individually and as an
aggregate.

But if these widely-dispersed moving masses mutually gravitate, what
must happen? There appears but one tenable answer. Even supposing they
were all absolutely equal in weight, and arranged into an annulus with
absolute regularity, and endowed with exactly the amounts of centrifugal
force required to prevent nearer approach to their common centre of
gravity; the condition would still be one which the slightest disturbing
force would destroy. Much more then are we driven to the inference, that
our actual Sidereal System cannot preserve its present arrangement: the
irregularities of its distribution being such as to render even a
temporary moving equilibrium impossible. If the stars are so many
centres of an attractive force that varies inversely as the square of
the distance, there appears to be no escape from the conclusion, that
the structure of our galaxy must be undergoing change; and must continue
to undergo change.

Thus, in the absence of tenable alternatives, we are brought to the
positions:�1, that the stars are in motion;�2, that they move in
conformity with the law of gravitation;�3, that, distributed as they
are, they cannot move in conformity with the law of gravitation, without
undergoing change of arrangement. If now we permit ourselves to take a
further step, and ask the nature of this change of arrangement, we find
ourselves obliged to infer a progressive concentration. Whether we do or
do not suppose the clustering which is now visible, to have been caused
by mutual gravitation acting throughout past eras, as the hypothesis of
Evolution implies, we are equally compelled to conclude that this
clustering must increase throughout future eras. Stars at present
dispersed, must become locally aggregated; existing aggregations, at the
same time that they are enlarged by the drawing in of adjacent stars,
must grow more dense; and aggregations must coalesce with each other:
each greater degree of concentration augmenting the force by which
further concentration is produced.

And now what must be the limit of this concentration? The mutual
attraction of two individual stars, when it so far predominates over
other attractions as to cause approximation, almost certainly ends in
the formation of a binary star; since the motions generated by other
attractions, prevent the two stars from moving in straight lines to
their common centre of gravity. Between small clusters, too, having also
certain proper motions as clusters, mutual attraction may lead, not to
complete union, but to the formation of binary clusters. As the process
continues however, and the clusters become larger, it seems clear that
they must move more directly towards each other, thus forming clusters
of increasing density; and that eventually all clusters must unite into
one comparatively close aggregation. While, therefore, during the
earlier stages of concentration, the probabilities are immense against
the actual contact of these mutually-gravitating masses; it is tolerably
manifest, that as the concentration increases, collision must become
probable, and ultimately certain. This is an inference not lacking the
support of high authority. Sir John Herschel, treating of those numerous
and variously-aggregated clusters of stars revealed by the telescope,
and citing with apparent approval his father�s opinion, that the more
diffused and irregular of these, are �globular clusters in a less
advanced state of condensation;� subsequently remarks, that �among a
crowd of solid bodies of whatever size, animated by independent and
partially opposing impulses, motions opposite to each other _must_
produce collision, destruction of velocity, and subsidence or near
approach towards the centre of preponderant attraction; while those
which conspire, or which remain outstanding after such conflicts, _must_
ultimately give rise to circulation of a permanent character.� Now what
is here alleged of these minor sidereal aggregations, cannot be denied
of the large aggregations; and thus the above-described process of
concentration, appears certain to bring about an increasingly-frequent
integration of masses.

We have next to consider the consequences of the accompanying loss of
velocity. The sensible motion which disappears, cannot be destroyed; but
must be transformed into insensible motion. What will be the effect of
this insensible motion? Some approach to a conception of it, will be
made by considering what would happen were the comparatively
insignificant motion of our planet thus transformed. In his essay on
�The Inter-action of Natural Forces,� Prof. Helmholtz states the thermal
equivalent of the Earth�s movement through space; as calculated on the
now received datum of Mr. Joule. �If our Earth,� he says, �were by a
sudden shock brought to rest in her orbit,�which is not to be feared in
the existing arrangement of our system�by such a shock a quantity of
heat would be generated equal to that produced by the combustion of
fourteen such Earths of solid coal. Making the most unfavourable
assumption as to its capacity for heat, that is, placing it equal to
that of water, the mass of the Earth would thereby be heated 11,200
degrees; it would therefore be quite fused, and for the most part
reduced to vapour. If then the Earth, after having been thus brought to
rest, should fall into the Sun, which of course would be the case, the
quantity of heat developed by the shock would be 400 times greater.� Now
so relatively small a momentum as that acquired by the Earth in falling
through 95,000,000 of miles to the Sun, being equivalent to a molecular
motion such as would reduce the Earth to gases of extreme rarity; what
must be the molecular motion generated by the mutually-arrested momenta
of two stars, that have moved to their common centre of gravity through
spaces immeasurably greater? There seems no alternative but to conclude,
that this molecular motion must be so great, as to reduce the matter of
the stars to an almost inconceivable tenuity�a tenuity like that which
we ascribe to nebular matter.       Such being the immediate effect of
the integration of any two stars in a concentrating aggregate, what must
be the ulterior effect on the aggregate as a whole? Sir John Herschel,
in the passage above quoted, describing the collisions that must arise
in a mutually-gravitating group of stars, adds that those stars �which
remain outstanding after such conflicts, _must_ ultimately give rise to
circulation of a permanent character.� The problem, however, is here
dealt with purely as a mechanical one: the assumption being, that the
mutually-arrested masses will continue as masses�an assumption to which
no objection was apparent at the time when Sir John Herschel wrote this
passage; since the doctrine of the correlation of forces was not then
recognized. But obliged as we now are to conclude, that stars moving at
the high velocities acquired during concentration, will, by mutual
arrest, be dissipated into gases of great tenuity, the problem becomes
different; and a different inference appears unavoidable. For the
diffused matter produced by such conflicts, must form a resisting
medium, occupying that central region of the aggregate through which its
members from time to time pass in describing their orbits�a resisting
medium which they cannot move through without having their velocities
diminished. Every further such collision, by augmenting this resisting
medium, and making the losses of velocity greater, must further aid in
preventing the establishment of that equilibrium which would else arise;
and so must conspire to produce more frequent collisions. And the
nebulous matter thus formed, presently enveloping and extending beyond
the whole aggregate, must, by continuing to shorten their gyrations,
entail an increasingly-active integration and re-active disintegration
of the moving masses; until they are all finally dissipated.       This,
indeed, is the conclusion which, leaving out all consideration of the
process gone through, presents itself as a simple deduction from the
persistence of force. If the stars have been, and still are,
concentrating however indirectly on their common centre of gravity, and
must eventually reach it; it is a corollary from the persistence of
force, that the quantities of motion they have severally acquired, must
suffice to carry them away from the common centre of gravity to those
remote regions whence they originally began to move towards it. And
since, by the conditions of the case, they cannot return to these remote
regions in the shape of concrete masses, they must return in the shape
of diffused masses. Action and reaction being equal and opposite, the
momentum producing dispersion, must be as great as the momentum acquired
by aggregation; and being spread over the same quantity of matter, must
cause an equivalent distribution through space, whatever be the form of
the matter.       One condition, however, essential to the literal
fulfilment of this result, must be specified; namely, that the quantity
of molecular motion produced and radiated into space by each star in the
course of its formation from diffused matter, shall be compensated by an
equal quantity of molecular motion radiated from other parts of space
into the space which our Sidereal System occupies. In other words, if we
set out with that amount of molecular motion implied by the existence of
the matter of our Sidereal System in a nebulous form; then it follows
from the persistence of force, that if this matter undergoes the
re-distribution constituting Evolution, the quantity of molecular motion
given out during the integration of each mass, plus the quantity of
molecular motion given out during the integration of all the masses,
must suffice again to reduce it to the same nebulous form.       Here
indeed we arrive at an impassable limit to our reasonings; since we
cannot know whether this condition is or is not fulfilled. On the
hypothesis of an unlimited space, containing, at certain intervals,
Sidereal Systems like our own, it may be that the quantity of molecular
motion radiated into the region occupied by our Sidereal System, is
equal to that which our Sidereal System radiates; in which case the
quantity of motion possessed by it, remaining undiminished, our Sidereal
System may continue during unlimited time, to repeat this alternate
concentration and diffusion. But if, on the other hand, throughout
boundless space there exist no other Sidereal Systems subject to like
changes, or if such other Sidereal Systems exist at more than a certain
average distance from each other; then it seems an unavoidable
conclusion that the quantity of motion possessed, must diminish by
radiation into unoccupied space; and that so, on each successive
resumption of the nebulous form, the matter of our Sidereal System will
occupy a less space; until at the end of an infinite time it reaches
either a state in which its concentrations and diffusions are relatively
small, or a state of complete aggregation and rest. Since, however, we
have no evidence showing the existence or non-existence of Sidereal
Systems throughout remote space; and since, even had we such evidence, a
legitimate conclusion could not be drawn from premises of which one
element (unlimited space) is inconceivable; we must be for ever without
answer to this transcendent question. All we can say is, that so far as
the data enable us to judge, the integration of our Sidereal System will
be followed by disintegration; that such integration and disintegration
will be repeated; and that, for anything we know to the contrary, the
alternation of them may continue without limit.

But leaving this ultimate insoluble problem, and confining ourselves to
the proximate and not necessarily insoluble one, we find reason for
thinking that after the completion of those various equilibrations which
bring to a close all the forms of Evolution we have contemplated, there
must still continue an equilibration of a far wider kind. When that
integration everywhere in progress throughout our Solar System, has
reached its climax, there will remain to be effected the immeasurably
greater integration of our Solar System, with all other such systems. As
in those minor forms now going on around us, this integration with its
concomitant equilibration, involves the change of aggregate motion into
diffused motion; so in those vaster forms hereafter to be carried out,
there must similarly be gained in molecular motion what is lost in the
motion of masses; and the inevitable transformation of this motion of
masses into molecular motion, cannot take place without reducing the
masses to a nebulous form. Thus we seem led to the conclusion that the
entire process of things, as displayed in the aggregate of the visible
Universe, is analogous to the entire process of things as displayed in
the smallest aggregates. Where, as in organic bodies, the whole series
of changes constituting Evolution can be traced, we saw that,
dynamically considered, Evolution is a change from molecular motion to
the motion of masses; and this change, becoming more active during the
ascending phase of Evolution while the masses increase in bulk and
heterogeneity, eventually begins to get less active; until, passing
through stages in which the integration grows greater, and the
equilibrium more definite, it finally ceases; whereupon there arises, by
an ulterior process, an increase of molecular motion, ending in the more
or less complete dissolution of the aggregate. And here we find reason
to believe that, along with each of the thousands of similar ones
dispersed through the heavens, our Solar System, after passing through
stages during which the motion of masses is produced at the expense of
lost molecular motion, and during which there goes on an increasingly
active differentiation and integration, arrives at a climax whence these
changes, beginning to decline in activity, slowly bring about that
complete integration and equilibration which in other cases we call
death; and that there afterwards comes a time, when the still-remaining
motions of masses are transformed into a molecular motion which causes
dissolution of the masses. Motion as well as Matter being fixed in
quantity, it would seem that the change in the distribution of Matter
which Motion effects, coming to a limit in whichever direction it is
carried, the indestructible Motion thereupon necessitates a reverse
distribution. Apparently, the universally-coexistent forces of
attraction and repulsion, which, as we have seen, necessitate rhythm in
all minor changes throughout the Universe, also necessitate rhythm in
the totality of its changes�produce now an immeasurable period during
which the attractive forces predominating, cause universal
concentration, and then an immeasurable period during which the
repulsive forces predominating, cause universal diffusion�alternate eras
of Evolution and Dissolution. And thus there is suggested the conception
of a past during which there have been successive Evolutions similar to
that which is now going on; and a future during which successive other
such Evolutions may go on.

Let none suppose, however, that this is to be taken as anything more
than a speculation. In dealing with times and spaces and forces so
immensely transcending those of which we have definite experience, we
are in danger of passing the limits to human intelligence. Though these
times and spaces and forces cannot literally be classed as infinite; yet
they are so utterly beyond the possibility of definite conception, as to
be almost equally unthinkable with the infinite. What has been above
said, should therefore be regarded simply as a possible answer to a
possible doubt. When, pushing to its extreme the argument that Evolution
must come to a close in complete equilibrium or rest, the reader
suggests that for aught which appears to the contrary, the Universal
Death thus implied will continue indefinitely; it is legitimate to point
out how, on carrying the argument still further, we are led to infer a
subsequent Universal Life. But while this last inference may fitly be
accepted as a demurrer to the first, it would be unwise to accept it in
any more positive sense.

                  *       *       *       *       *

§ 137. Returning from this parenthetical discussion, concerning the
probable or possible state of things that may arise after Evolution has
run its course; and confining ourselves to the changes constituting
Evolution, with which alone we are immediately concerned; we have now to
inquire whether the cessation of these changes, in common with all their
transitional characteristics, admits of _à priori_ proof. It will soon
become apparent that equilibration, not less than the preceding general
principles, is deducible from the persistence of force.

We have seen (§ 85) that phenomena are interpretable only as the results
of universally-coexistent forces of attraction and repulsion. These
universally-coexistent forces of attraction and repulsion, are, indeed,
the complementary aspects of that absolutely persistent force which is
the ultimate datum of consciousness. Just in the same way that the
equality of action and re-action is a corollary from the persistence of
force, since their inequality would imply the disappearance of the
differential force into nothing, or its appearance out of nothing; so,
we cannot become conscious of an attractive force without becoming
simultaneously conscious of an equal and opposite repulsive force. For
every experience of a muscular tension, (under which form alone we can
immediately know an attractive force,) presupposes an equivalent
resistance�a resistance shown in the counter-balancing pressure of the
body against neighbouring objects, or in that absorption of force which
gives motion to the body, or in both�a resistance which we cannot
conceive as other than equal to the tension, without conceiving force to
have either appeared or disappeared, and so denying the persistence of
force. And from this necessary correlation, results our inability,
before pointed out, of interpreting any phenomena save in terms of these
correlatives�an inability shown alike in the compulsion we are under to
think of the statical forces which tangible matter displays, as due to
the attraction and repulsion of its atoms, and in the compulsion we are
under to think of dynamical forces exercised through space, by regarding
space as filled with atoms similarly endowed. Thus from the existence of
a force that is for ever unchangeable in quantity, there follows, as a
necessary corollary, the co-extensive existence of these opposite forms
of force�forms under which the conditions of our consciousness oblige us
to represent that absolute force which transcends our knowledge.

But the forces of attraction and repulsion being universally
co-existent, it follows, as before shown, that all motion is motion
under resistance. Units of matter, solid, liquid, aëriform, or ethereal,
filling the space which any moving body traverses, offer to such body
the resistance consequent on their cohesion, or their inertia, or both.
In other words, the denser or rarer medium which occupies the places
from moment to moment passed through by such moving body, having to be
expelled from them, as much motion is abstracted from the moving body as
is given to the medium in expelling it from these places. This being the
condition under which all motion occurs, two corollaries result. The
first is, that the deductions perpetually made by the communication of
motion to the resisting medium, cannot but bring the motion of the body
to an end in a longer or shorter time. The second is, that the motion of
the body cannot cease until these deductions destroy it. In other words,
movement must continue till equilibration takes place; and equilibration
must eventually take place. Both these are manifest deductions from the
persistence of force. To say that the whole or part of a body�s motion
can disappear, save by transfer to something which resists its motion,
is to say that the whole or part of its motion can disappear without
effect; which is to deny the persistence of force. Conversely, to say
that the medium traversed can be moved out of the body�s path, without
deducting from the body�s motion, is to say that motion of the medium
can arise out of nothing; which is to deny the persistence of force.
Hence this primordial truth is our immediate warrant for the
conclusions, that the changes which Evolution presents, cannot end until
equilibrium is reached; and that equilibrium must at last be reached.

Equally necessary, because equally deducible from this same truth that
transcends proof, are the foregoing propositions respecting the
establishment and maintenance of moving equilibria, under their several
aspects. It follows from the persistence of force, that the various
motions possessed by any aggregate, either as a whole or among its
parts, must be severally dissipated by the resistances they severally
encounter; and that thus, such of them as are least in amount, or meet
with greatest opposition, or both, will be brought to a close while the
others continue. Hence in every diversely moving aggregate, there
results a comparatively early dissipation of motions which are smaller
and much resisted; followed by long-continuance of the larger and
less-resisted motions; and so there arise dependent and independent
moving equilibria. Hence also may be inferred the tendency to
conservation of such moving equilibria; since, whenever the new motion
given to the parts of a moving equilibrium by a disturbing force, is not
of such kind and amount that it cannot be dissipated before the
pre-existing motions (in which case it brings the moving equilibrium to
an end) it must be of such kind and amount that it can be dissipated
before the pre-existing motions (in which case the moving equilibrium is
re-established).

Thus from the persistence of force follow, not only the various direct
and indirect equilibrations going on around, together with that cosmical
equilibration which brings Evolution under all its forms to a close; but
also those less manifest equilibrations shown in the re-adjustments of
moving equilibria that have been disturbed. By this ultimate principle
is proveable the tendency of every organism, disordered by some unusual
influence, to return to a balanced state. To it also may be traced the
capacity, possessed in a slight degree by individuals, and in a greater
degree by species, of becoming adapted to new circumstances. And not
less does it afford a basis for the inference, that there is a gradual
advance towards harmony between man�s mental nature and the conditions
of his existence. After finding that from it are deducible the various
characteristics of Evolution, we finally draw from it a warrant for the
belief, that Evolution can end only in the establishment of the greatest
perfection and the most complete happiness.

-----

Footnote 18:

  Sir David Brewster has recently been citing with approval, a
  calculation by M. Babinet, to the effect that on the hypothesis of
  nebular genesis, the matter of the Sun, when it filled the Earth�s
  orbit, must have taken 3181 years to rotate; and that therefore the
  hypothesis cannot be true. This calculation of M. Babinet may pair-off
  with that of M. Comte, who, contrariwise, made the time of this
  rotation agree very nearly with the Earth�s period of revolution round
  the Sun; for if M. Comte�s calculation involved a _petitio principii_,
  that of M. Babinet is manifestly based on two assumptions, both of
  which are gratuitous, and one of them totally inconsistent with the
  doctrine to be tested. He has evidently proceeded on the current
  supposition respecting the Sun�s internal density, which is not
  proved, and from which there are reasons for dissenting; and he has
  evidently taken for granted that all parts of the nebulous spheroid,
  when it filled the Earth�s orbit, had the same angular velocity;
  whereas if (as is implied in the nebular hypothesis, rationally
  understood) this spheroid resulted from the concentration of far more
  widely-diffused matter, the angular velocity of its equatorial portion
  would obviously be immensely greater than that of its central portion.

Footnote 19:

  See paper �On the Inter-action of Natural Forces,� by Prof. Helmholtz,
  translated by Prof. Tyndall, and published in the _Philosophical
  Magazine_, supplement to Vol. XI. fourth series.

Footnote 20:

  Until I recently consulted his �Outlines of Astronomy� on another
  question, I was not aware that so far back as 1833, Sir John Herschel
  had enunciated the doctrine that �the sun�s rays are the ultimate
  source of almost every motion which takes place on the surface of the
  earth.� He expressly includes all geologic, meteorologic, and vital
  actions; as also those which we produce by the combustion of coal. The
  late George Stephenson appears to have been wrongly credited with this
  last idea.




                             CHAPTER XVII.
                        SUMMARY AND CONCLUSION.


§ 138. In the chapter on �Laws in general,� after delineating the
progress of mankind in recognizing uniformities of relation among
surrounding phenomena�after showing how the actual succession in the
establishment of different orders of co-existences and sequences,
corresponds with the succession deducible _à priori_ from the conditions
to human knowledge�after showing how, by the ever-multiplying
experiences of constant connections among phenomena, there has been
gradually generated the conception of universal conformity to law; it
was suggested that this conception will become still clearer, when it is
perceived that there are laws of wider generality than any of those at
present accepted.

The existence of such more general laws, is, indeed, almost implied by
the _ensemble_ of the facts set forth in the above-named chapter; since
they make it apparent, that the process hitherto carried on, of bringing
phenomena under fewer and wider laws, has not ceased, but is advancing
with increasing rapidity. Apart, however, from evidence of this kind,
the man of science, hourly impressed with new proof of uniformity in the
relations of things, until the conception of uniformity has become with
him a necessity of thought, tacitly entertains the conclusion that the
minor uniformities which Science has thus far established, will
eventually be merged in uniformities that are universal. Taught as he is
by every observation and experiment, to regard phenomena as
manifestations of Force; and learning as he does to contemplate Force as
unchangeable in amount; there tends to grow up in him a belief in
unchangeable laws common to Force under all its manifestations. Though
he may not have formulated it to himself, he is prepared to recognize
the truth, that, being fixed in quantity, fixed in its two ultimate
modes of presentation (Matter and Motion), and fixed in the conditions
under which it is presented (Time and Space); Force must have certain
equally fixed laws of action, common to all the changes it produces.

Hence to the classes who alone are likely to read these pages, the
hypothesis of a fundamental unity, extending from the simplest inorganic
actions up to the most complex associations of thought and the most
involved social processes, will have an _à priori_ probability. All
things being recognized as having one source, will be expected to
exhibit one method. Even in the absence of a clue to uniformities
co-extensive with all modes of Force, as the mathematical uniformities
are co-extensive with Space and Time, it will be inferred that such
uniformities exist. And thus a certain presumption will result in favour
of any formula, of a generality great enough to include concrete
phenomena of every order.

                  *       *       *       *       *

§ 139. In the chapters on the �Law of Evolution,� there was set forth a
principle, which, so far as accessible evidence enables us to judge,
possesses this universality. The order of material changes, first
perceived to have certain constant characteristics in cases where it
could be readily traced from beginning to end, we found to have these
same characteristics in cases where it could be less readily traced; and
we saw numerous indications that these same characteristics were
displayed during past changes of which we have no direct knowledge. The
transformation of the homogeneous into the heterogeneous, first observed
by naturalists to be exhibited during the development of every plant and
animal, proved to be also exhibited during the development of every
society; both in its political and industrial organization, and in all
the products of social life,�language, science, art, and literature.
From the disclosures of geology, we drew adequate support for the
conclusion, that in the structure of the Earth there has similarly been
a progress from uniformity, through ever-increasing degrees of
multiformity, to the complex state which we now see. And on the
assumption of that nebular origin to which so many facts point, we
inferred that a like transition from unity to variety of distribution,
must have been undergone by our Solar System; as well as by that vast
assemblage of such systems constituting the visible Universe.       This
definition of the metamorphosis, first asserted by physiologists of
organic aggregates only, but which we thus found reason to think, holds
of all other aggregates, proved on further inquiry to be too wide. Its
undue width was shown to arise from the omission of certain other
characteristics, that are, not less than the foregoing one, displayed
throughout all kinds of Evolution. We saw that simultaneously with the
change from homogeneity to heterogeneity, there takes place a change
from indefiniteness of arrangement to definiteness of arrangement�a
change everywhere equally traceable with that which it accompanies.
Further consideration made it apparent, that the increasing definiteness
thus manifested along with increasing heterogeneity, necessarily results
from increasing integration of the parts severally rendered unlike. And
thus we finally reached the conclusion, that there has been going on
throughout an immeasurable past, is still going on, and will continue to
go on, an advance from a diffused, indeterminate, and uniform
distribution of Matter, to a concentrated, determinate, and multiform
distribution of it.

At a subsequent stage of our inquiry, we discovered that this
progressive change in the arrangement of Matter, is accompanied by a
parallel change in the arrangement of Motion�that every increase in the
structural complexity of things, involves a corresponding increase in
their functional complexity. It was shown that along with the
integration of molecules into masses, there arises an integration of
molecular motion into the motion of masses; and that as fast as there
results variety in the sizes and forms of aggregates and their relations
to incident forces, there also results variety in their movements.
Whence it became manifest, that the general process of things is from a
confused simplicity to an orderly complexity, in the distribution of
both Matter and Motion.

It was pointed out, however, that though this species of transformation
is universal, in the sense of holding throughout all classes of
phenomena, it is not universal in the sense of being continued without
limit in all classes of phenomena. Those aggregates which exhibit the
entire change from uniformity to multiformity of structure and function,
in comparatively short periods, eventually show us a reverse set of
changes: Evolution is followed by Dissolution. The differentiations and
integrations of Matter and Motion, finally reach a degree which the
conditions do not allow them to pass; and there then sets in a process
of disintegration and assimilation, of both the parts and the movements
that were before growing more united and more distinct.

But under one or the other of these processes, all observable
modifications in the arrangement of things may be classed. Every change
comes under the head of integration or disintegration, material or
dynamical; or under the head of differentiation or assimilation,
material or dynamical; or under both. Each inorganic mass is either
undergoing increase by the combination with it of surrounding elements
for which its parts have affinity; or undergoing decrease by the solvent
and abraiding action of surrounding elements; or both one and the other
in varied succession and combination. By perpetual additions and losses
of heat, it is having its parts temporarily differentiated from each
other, or temporarily assimilated to each other, in molecular state. And
through the actions of divers agents, it is also undergoing certain
permanent molecular re-arrangements; rendering it either more uniform or
more multiform in structure. These opposite kinds of change, thus
vaguely typified in every surrounding fragment of matter, are displayed
in all aggregates with increasing distinctness in proportion as the
conditions essential to re-arrangement of parts are fulfilled. So that
universally, the process of things is either in the one direction or the
other. There is in all cases going on that ever-complicating
distribution of Matter and Motion which we call Evolution; save in those
cases where it has been brought to a close and reversed by what we call
Dissolution.

                  *       *       *       *       *

§ 140. Whether this omnipresent metamorphosis admits of interpretation,
was the inquiry on which we next entered. Recognizing the changes thus
formulated as consisting in Motions of Matter that are produced by
Force, we saw that if they are interpretable at all, it must be by the
affiliation of them on certain ultimate laws of Matter, Motion, and
Force. We therefore proceeded to inquire what these ultimate laws are.

We first contemplated under its leading aspects, the principle of
correlation and equivalence among forces. The genesis of sensible motion
by insensible motion, and of insensible motion by sensible motion, as
well as the like reciprocal production of those forms of insensible
motion which constitute Light, Heat, Electricity, Magnetism, and
Chemical Action, was shown to be a now accepted doctrine, that involves
certain corollaries respecting the processes everywhere going on around
us. Setting out with the probability that the insensible motion radiated
by the Sun, is the transformed product of the sensible motion lost
during the progressive concentration of the solar mass; we saw that by
this insensible motion, are in turn produced the various kinds of
sensible motion on the Earth�s surface. Besides the inorganic
terrestrial changes, we found that the changes constituting organic life
are thus originated. We were obliged to conclude that within this
category, come the vital phenomena classed as mental, as well as those
classed as physical. And it appeared inevitably to follow that of social
changes, too, the like must be said.       We next saw that phenomena
being cognizable by us only as products of Force, manifested under the
two-fold form of attraction and repulsion, there results the general law
that all Motion must occur in the direction of least resistance, or in
the direction of greatest traction, or in the direction of their
resultant. It was pointed out that this law is every instant illustrated
in the movements of the celestial bodies. The innumerable transpositions
of matter, gaseous, liquid, and solid, going on over the Earth�s
surface, were shown to conform to it. Evidence was given that this same
ultimate principle of motion underlies the structural and functional
changes of organisms. Throughout the succession of those nervous actions
which constitute thought and feeling, as also in the discharge of
feeling into action, we no less found this principle conspicuous. Nor
did we discover any exception to it in the movements, temporary and
permanent, that go on in societies.       From the universal coexistence
of opposing forces, there also resulted the rhythm of motion. It was
shown that this is displayed from the infinitesimal vibrations of
molecules up to the enormous revolutions and gyrations of planets; that
it is traceable throughout all meteorologic and geologic changes; that
the functions of every organic body exemplify it in various forms; that
mental activities too, intellectual and emotional, exhibit periodicities
of sundry kinds; and that actions and reactions illustrating this law
under a still more complex form, pervade social processes.

Such being the principles to which conform all changes produced by
Force on the distribution of Matter, and all changes re-actively
produced by Matter on the distribution of Force, we proceeded to
inquire what must be the consequent nature of any re-distributions
produced: having first noted the limiting conditions between which
such re-distributions are possible, and the medium conditions that are
most favourable to them.       The first conclusion arrived at, was,
that any finite homogeneous aggregate must inevitably lose its
homogeneity, through the unequal exposure of its parts to incident
forces. We observed how this was shown in surrounding things, by the
habitual establishment of differences between inner and outer parts,
and parts otherwise dissimilarly circumstanced. It was pointed out
that the production of diversities of structure by forces acting under
diverse conditions, has been illustrated in astronomic evolution,
supposing such evolution to have taken place; and that a like
connection of cause and effect is seen in the large and small
modifications undergone by our globe. In the early changes of organic
germs, we discovered further evidence that unlikenesses of structure
follow unlikenesses of relations to surrounding agencies�evidence
enforced by the tendency of the differently-placed members of each
species to diverge into varieties. We found that the principle is also
conformed to in the establishment of distinctions among our ideas; and
that the contrasts, political and industrial, that arise between the
parts of societies are no less in harmony with it. The instability of
the homogeneous thus caused, and thus everywhere exemplified, we also
saw must hold of the unlike parts into which any uniform whole lapses;
and that so the less heterogeneous must tend continually to become
more heterogeneous�an inference which we also found to be everywhere
confirmed by fact.       Carrying a step further our inquiry into
these actions and reactions between Force and Matter, there was
disclosed a secondary cause of increasing multiformity. Every
differentiated part becomes, we found, a parent of further
differentiations; not only in the sense that it must lose its own
homogeneity in heterogeneity, but also in the sense that it must, in
growing unlike other parts, become a centre of unlike reactions on
incident forces; and by so adding to the diversity of forces at work,
must add to the diversity of effects produced. This multiplication of
effects, likewise proved to be manifest throughout all Nature. That
forces modified in kind and direction by every part of every
aggregate, are gradually expended in working changes that grow more
numerous and more varied as the forces are subdivided, is shown in the
actions and reactions going on throughout the Solar System, in the
never-ceasing geologic complications, in the involved symptoms
produced in organisms by disturbing influences, in the many thoughts
and feelings generated by single impressions, and in the
ever-ramifying results of each new agency brought to bear on a
society. To which add the corollary, confirmed by abundant facts, that
the multiplication of effects must increase in a geometrical
progression, as the heterogeneity increases.       Completely to
interpret the structural changes constituting Evolution, there
remained to assign a reason for that increasingly-distinct demarcation
of parts, which accompanies the production of differences between
parts. This reason we discovered to be, the segregation of mixed units
under the action of forces capable of moving them. We saw that when
the parts of an aggregate have been made qualitatively unlike by
unlike incident forces�that is, when they have become contrasted in
the natures of their component units; there necessarily arises a
tendency to separation of the dissimilar orders of units from each
other, and to aggregation of those units which are similar. This cause
of the integration that accompanies differentiation, turned out to be
likewise exemplified by all kinds of Evolution�by the formation of
celestial bodies, by the moulding of the Earth�s crust, by organic
modifications, by the establishment of mental distinctions, by the
genesis of social divisions. And we inferred, what we may everywhere
see, that the segregation thus produced goes on so long as there
remains a possibility of making it more complete.       At length, to
the query whether the processes thus traced out have any limit, there
came the answer that they must end in equilibration. That continual
division and subdivision of forces, which is instrumental in changing
the uniform into the multiform and the multiform into the more
multiform, we saw to be at the same time a process by which force is
perpetually dissipated; and that dissipation, continuing as long as
there remains any force unbalanced by an opposing force, must end in
rest. It was shown that when, as happens with aggregates of various
orders, a number of movements are going on in combination, the earlier
dispersion of the smaller and more resisted movements, entails the
establishment of different kinds of moving equilibria: forming
transitional stages on the way to complete equilibrium. And further
inquiry made it apparent that for the same reason, these moving
equilibria have a certain self-conserving power; shown in the
neutralization of perturbations, and the adjustment to new conditions.
This general principle, like the preceding ones, proved to be
traceable throughout all forms of Evolution�astronomic, geologic,
biologic, mental and social. And our concluding inference was, that
the penultimate stage of this process, in which the extremest degree
of multiformity and completest form of moving equilibrium is
established, must be one implying the highest conceivable state of
humanity.

Thus it became apparent that this transformation of on indefinite,
incoherent homogeneity into a definite coherent heterogeneity, which
goes on everywhere, until it brings about a reverse transformation, is
consequent on certain simple laws of force. Given those universal modes
of action which are from moment to moment illustrated in the commonest
changes around us, and it follows that there cannot but result the
observed metamorphosis of an indeterminate uniformity into a determinate
multiformity.

                  *       *       *       *       *

§ 141. Finally, we have asked whether, for these universal modes of
action, any common cause is assignable�whether these wide truths are
dependent on any single widest truth. And to this question we found a
positive answer. These several principles are corollaries from that
primordial principle which transcends human intelligence by underlying
it.

In the first part of this work it was shown, by analysis of both our
religious and our scientific ideas, that while knowledge of the cause
which produces effects on our consciousness is impossible, the existence
of a cause for these effects is a datum of consciousness. Though Being
is cognizable by us only under limits of Time and Space, yet Being
without limits of Time and Space was proved to be the indefinite
cognition forming the necessary basis of our definite cognitions. We saw
that the belief in an Omnipresent Power of which no commencement or
cessation can be conceived, is that fundamental element in Religion
which survives all its changes of form. We saw that all Philosophies
avowedly or tacitly recognize this same ultimate truth:�that while the
Relativist rightly repudiates those definite assertions which the
Absolutist makes respecting real existence, he is yet at last compelled
to unite with him in predicating real existence. And this inexpugnable
consciousness in which Religion and Philosophy are at one with Common
Sense, proved to be likewise that on which all exact Science is founded.
We found that subjective Science can give no account of those
conditioned modes of existence which constitute consciousness, without
postulating unconditioned existence. And we found that objective Science
can give no account of the existence which we know as external, without
regarding its changes of form as manifestations of an existence that
continues constant under all forms. Absolute Being, or Being which
persists without beginning or end, was shown to be the common datum of
all human thought; for the sufficient reason that the consciousness of
it cannot be suppressed, without the suppression of consciousness
itself.

From this truth which transcends proof, we have seen that the general
principles above set down, are deducible. That the power or force
manifested to us in all phenomena, continues unaltered in quantity,
however its mode of manifestation be altered, is a proposition in which
these several propositions are involved. It was shown that on the
Persistence of Force are based the demonstrations that Matter is
indestructible and Motion continuous. When its proofs were examined, the
correlation and equivalence of forces was found to follow from the
Persistence of Force. The necessity we are under of conceiving Force
under the two-fold form of attraction and repulsion, turns out to be but
an implication of the necessity we are under of conceiving Force as
persistent. On the Persistence of Force, we saw that the law of
direction of Motion is dependent; and from it also we saw that the
rhythm of Motion necessarily results. Passing to those changes of
distribution which, by the Motion it generates, Force produces in
Matter, it was pointed out that from the Persistence of Force are
severally deducible, the instability of the homogeneous, the
multiplication of effects, and that increasing definiteness of structure
to which continuous differentiation and integration leads. And lastly we
saw that Force being persistent, Evolution cannot cease until
equilibrium is reached; and that equilibrium must eventually be reached.

So that given Force manifested in Time and Space, under the forms of
Matter and Motion; and it is demonstrable, _à priori_, that there must
go on such transformations as we find going on.

                  *       *       *       *       *

§ 142. See then the accumulation of proofs. The advance of human
intelligence in establishing laws continually wider in generality,
raises the presumption that there are all-comprehensive laws. Turning to
the facts, we discern a pervading uniformity in the general course of
things where this can be watched, and indications of such uniformity
where it cannot be watched. Considering this uniformity analytically, we
find it to result from certain simpler uniformities in the actions of
Force. And these uniformities prove to be so many necessary implications
of that primordial truth which underlies all knowledge�the Persistence
of Force. The aspect of things raises a presumption; extended
observations lead to an induction that fulfils this presumption; this
induction is deductively confirmed; and the laws whence it is deduced
are corollaries from that datum without which thought is impossible.

No higher degree of verification than this can be imagined. An induction
based on facts so numerous and varied, and falling short of universality
only where the facts are beyond observation, possesses of itself a
validity greater than that of most scientific inductions. When it is
shown that the proposition thus arrived at _à posteriori_, may also be
arrived at _à priori_, starting from certain simple laws of force; it is
raised to a level with those generalizations of concrete science which
are accepted as proved. And when these simple laws of force are
affiliated upon that ultimate truth which transcends proof; this
dependent proposition takes rank with those propositions of abstract
science which are our types of the greatest conceivable certainty.

Let no one suppose that any such degree of certainty is alleged of the
various minor propositions brought in illustration of the general
argument. Such an assumption would be so manifestly absurd, that it
seems scarcely needful to disclaim it. But the truth of the doctrine as
a whole, is unaffected by errors in the details of its presentation. As
the first principles of mathematics are not invalidated by mistakes made
in working out particular equations; so the first principles set forth
in the foregoing pages, do not stand or fall with each special statement
made in them. If it can be shown that the Persistence of Force is not a
datum of consciousness; or if it can be shown that the several laws of
force above specified are not corollaries from it; then, indeed, it will
be shown that the theory of Evolution has not the certainty here claimed
for it. But nothing short of this can invalidate the general conclusions
arrived at.

                  *       *       *       *       *

§ 143. If these conclusions be accepted�if it be admitted that they
inevitably follow from the truth transcending all others in authority�if
it be agreed that the phenomena going on everywhere are parts of the
general process of Evolution, save where they are parts of the reverse
process of Dissolution; then it must be inferred that all phenomena
receive their complete interpretation, only when recognized as parts of
these processes. Regarded from the point of view here reached, each
change that takes place, is an incident in the course of the
ever-complicating distribution of Matter and Motion, except where it is
an incident in the course of the reverse distribution; and each such
change is fully understood, only when brought under those universal
principles of change, to which these transformations necessarily
conform.       Whence, indeed, it appears to be an unavoidable
conclusion, that the limit towards which Science is advancing, must be
reached when these formulæ are made all-comprehensive. Manifestly, the
perfection of Science, is a state in which all phenomena are seen to be
necessary implications of the Persistence of Force. In such a state, the
dependence of each phenomenon on the Persistence of Force, must be
proved either directly or indirectly�either by showing that it is a
corollary of the Persistence of Force, or by showing that it is a
corollary from some general proposition deduced from the Persistence of
Force. And since all phenomena are incidents in the re-distributions of
Matter and Motion; and since there are certain general principles,
deducible from the Persistence of Force, to which all these
re-distributions conform; it seems inferrable that ultimately all
phenomena, where not classed as consequences of the Persistence of
Force, must be classed as consequences of these derivative principles.

                  *       *       *       *       *

§ 144. Of course this development of Science into an organized aggregate
of direct and indirect deductions from the Persistence of Force, can be
achieved only in the remote future; and indeed cannot be completely
achieved even then. Scientific progress, is progress in that
equilibration of thought and things which we saw is going on, and must
continue to go on; but which cannot arrive at perfection in any finite
period, because it advances more slowly the further it advances. But
though Science can never be entirely reduced to this form; and though
only at a far distant time can it be brought nearly to this form; yet
much may even now be done in the way of rude approximation. Those who
are familiar with the present aspects of Science, must recognize in them
the broken outlines of a general organization. The possibility of
arranging the facts already accumulated, into the order rudely exhibited
in the foregoing pages, will itself incline them to the belief that our
knowledge may be put into a more connected shape than it at present has.
They will see the probability that many now isolated inductions, may be
reduced to the form of deductions from first principles. They will
suspect that inferences drawn from the ultimate laws of force, will lead
to the investigation and generalization of classes of facts hitherto
unexamined. And they will feel, not only that a greater degree of
certainty must be acquired by Science, as fast as its propositions are
directly or indirectly deduced from the highest of all truths; but also
that it must so be rendered a more efficient agent of further inquiry.

To bring scientific knowledge to such degree of logical coherence as is
at present possible, is a task to be achieved only by the combined
efforts of many. No one man can possess that encyclopedic information
required for rightly arranging even the truths already established. But
as progress is effected by increments�as all organization, beginning in
faint and blurred outlines, is completed by successive modifications and
additions; advantage may accrue from an attempt, however rude, to reduce
the facts already accumulated�or rather certain classes of them�to
something like co-ordination. Such must be the plea for the several
volumes which are to succeed this.

                  *       *       *       *       *

§ 145. A few closing words must be said, concerning the general bearings
of the doctrines that are now to be further developed. Before proceeding
to interpret the detailed phenomena of Life, and Mind, and Society, in
terms of Matter, Motion, and Force, the reader must be reminded in what
sense the interpretations are to be accepted. In spite of everything
said at the outset, there are probably some who have gained the
impression that those most general truths set forth in the preceding
chapters, together with the truths deducible from them, claim to be
something more than relative truths. And, notwithstanding all evidence
to the contrary, there will probably have arisen in not a few minds, the
conviction that the solutions which have been given, along with those to
be derived from them, are essentially materialistic. Let none persist in
these misconceptions.

As repeatedly shown in various ways, the deepest truths we can reach,
are simply statements of the widest uniformities in our experience of
the relations of Matter, Motion, and Force; and Matter, Motion, and
Force are but symbols of the Unknown Reality. That Power of which the
nature remains for ever inconceivable, and to which no limits in Time or
Space can be imagined, works in us certain effects. These effects have
certain likenesses of kind, the most general of which we class together
under the names of Matter, Motion, and Force; and between these effects
there are likenesses of connection, the most constant of which we class
as laws of the highest certainty. Analysis reduces these several kinds
of effect to one kind of effect; and these several kinds of uniformity
to one kind of uniformity. And the highest achievement of Science is the
interpretation of all orders of phenomena, as differently-conditioned
manifestations of this one kind of effect, under differently-conditioned
modes of this one kind of uniformity. But when Science has done this, it
has done nothing more than systematize our experience; and has in no
degree extended the limits of our experience. We can say no more than
before, whether the uniformities are as absolutely necessary, as they
have become to our thought relatively necessary. The utmost possibility
for us, is an interpretation of the process of things as it presents
itself to our limited consciousness; but how this process is related to
the actual process, we are unable to conceive, much less to know.

Similarly, it must be remembered that while the connection between the
phenomenal order and the ontological order is for ever inscrutable; so
is the connection between the conditioned forms of being and the
unconditioned form of being, for ever inscrutable. The interpretation of
all phenomena in terms of Matter, Motion, and Force, is nothing more
than the reduction of our complex symbols of thought, to the simplest
symbols; and when the equation has been brought to its lowest terms the
symbols remain symbols still. Hence the reasonings contained in the
foregoing pages, afford no support to either of the antagonist
hypotheses respecting the ultimate nature of things. Their implications
are no more materialistic than they are spiritualistic; and no more
spiritualistic than they are materialistic. Any argument which is
apparently furnished to either hypothesis, is neutralized by as good an
argument furnished to the other. The Materialist, seeing it to be a
necessary deduction from the law of correlation, that what exists in
consciousness under the form of feeling, is transformable into an
equivalent of mechanical motion, and by consequence into equivalents of
all the other forces which matter exhibits; may consider it therefore
demonstrated that the phenomena of consciousness are material phenomena.
But the Spiritualist, setting out with the same data, may argue with
equal cogency, that if the forces displayed by matter are cognizable
only under the shape of those equivalent amounts of consciousness which
they produce, it is to be inferred that these forces, when existing out
of consciousness, are of the same intrinsic nature as when existing in
consciousness; and that so is justified the spiritualistic conception of
the external world, as consisting of something essentially identical
with what we call mind. Manifestly, the establishment of correlation and
equivalence between the forces of the outer and the inner worlds, may be
used to assimilate either to the other; according as we set out with one
or other term. But he who rightly interprets the doctrine contained in
this work, will see that neither of these terms can be taken as
ultimate. He will see that though the relation of subject and object
renders necessary to us these antithetical conceptions of Spirit and
Matter; the one is no less than the other to be regarded as but a sign
of the Unknown Reality which underlies both.


                                THE END.


                     JOHN CHILDS AND SON, PRINTERS.

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                          TRANSCRIBER�S NOTES


 1. Changed �which takes place� to �which take place� on p. 315.
 2. Duplicated the large spaces in the original text.
 3. Silently corrected typographical errors.
 4. Retained anachronistic and non-standard spellings as printed.
 5. Enclosed italics font in _underscores_.