[1] Berthelot, _Essai de Mecanique Chimique._

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recognize dissipation as an inevitable attendant on inanimate transfer of energy.

But when we come to consider inanimate actions in relation to time, or time-rate of change, we find a new feature in the phenomena attending transfer of energy; a feature which is really involved in general statements as to the laws of physical interactions.[1] It is seen, that the att.i.tude of inanimate material systems is very generally, if not in all cases, r.e.t.a.r.dative of change--opposing it by effects generated by the primary action, which may be called "secondary" for convenience.

Further, it will be seen that these secondary effects are those concerned in bringing about the inevitable dissipation.

As example, let us endeavour to transfer gravitational potential energy contained in a ma.s.s raised above the surface of the Earth into an elastic body, which we can put into compression by resting the weight upon it. In this way work is done against elastic force and stored as elastic potential energy. We may deal with a metal spring, or with a ma.s.s of gas contained in a cylinder fitted with a piston upon which the weight may be placed. In either case we find the effect of compression is to raise the temperature of the substance, thus causing its

[1] Helmholtz, _Ice and Glaciers._ Atkinson's collection of his Popular Lectures. First Series, p.120. Quoted by Tate, _Heat_, p. 311.

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expansion or increased resistance to the descent of the weight.

And this resistance continues, with diminishing intensity, till all the heat generated is dissipated into the surrounding medium.

The secondary effect thus delays the final transfer of energy.

Again, if we suppose the gas in the cylinder replaced by a vapour in a state of saturation, the effect of increased pressure, as of a weight placed upon the piston, is to reduce the vapour to a liquid, thereby bringing about a great diminution of volume and proportional loss of gravitational potential by the weight. But this change will by no means be brought about instantaneously.

When a little of the vapour is condensed, this portion parts with latent heat of vaporisation, increasing the tension of the remainder, or raising its point of saturation, so that before the weight descends any further, this heat has to escape from the cylinder.

Many more such cases might be cited. The heating of india-rubber when expanded, its cooling when compressed, is a remarkable one; for at first sight it appears as if this must render it exceptional to the general law, most substances exhibiting the opposite thermal effects when stressed. However, here, too, the action of the stress is opposed by the secondary effects developed in the substance; for it is found that this substance contracts when heated, expands when cooled. Again, ice being a substance which contracts in melting, the effect of pressure is to facilitate melting, lowering its freezing point. But

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so soon as a little melting occurs, the resulting liquid calls on the residual ice for an amount of heat equivalent to the latent heat of liquefaction, and so by cooling the whole, r.e.t.a.r.ds the change.

Such particular cases ill.u.s.trate a principle controlling the interaction of matter and energy which seems universal in application save when evaded, as we shall see, by the ingenuity of life. This principle is not only revealed in the researches of the laboratory; it is manifest in the history of worlds and solar systems. Thus, consider the effects arising from the aggregation of matter in s.p.a.ce under the influence of the mutual attraction of the particles. The tendency here is loss of gravitational potential. The final approach is however r.e.t.a.r.ded by the temperature, or vis viva of the parts attending collision and compression. From this cause the great suns of s.p.a.ce radiate for ages before the final loss of potential is attained.

Clerk Maxwell[1] observes on the general principle that less force is required to produce a change in a body when the change is unopposed by constraints than when it is subjected to such.

From this if we a.s.sume the external forces acting upon a system not to rise above a certain potential (which is the order of nature), the constraints of secondary actions may, under certain circ.u.mstances, lead to final rejection of some of the energy, or, in any

[1] _Theory of Heat_, p. 131.

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case, to r.e.t.a.r.dation of change in the system--dissipation of energy being the result.[1]

As such constraints seem inherently present in the properties of matter, we may summarise as follows:

_The transfer of energy into any inanimate material system is attended by effects r.e.t.a.r.dative to the transfer and conducive to dissipation._

Was this the only possible dynamic order ruling in material systems it is quite certain the myriads of ants and pines never could have been, except all generated by creative act at vast primary expenditure of energy. Growth and reproduction would have been impossible in systems which r.e.t.a.r.ded change at every step and never proceeded in any direction but in that of dissipation.

Once created, indeed, it is conceivable that, as heat engines, they might have dragged out an existence of alternate life and death; life in the hours of sunshine, death in hours of darkness: no final death, however, their lot, till their parts were simply worn out by long use, never made good by repair. But the sustained and increasing activity of organized nature is a fact; therefore some other order of events must be possible.

[1] The law of Least Action, which has been applied, not alone in optics, but in many mechanical systems, appears physically based upon the restraint and r.e.t.a.r.dation opposing the transfer of energy in material systems.

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GENERAL DYNAMIC CONDITIONS ATTENDING ANIMATE ACTIONS

What is the actual dynamic att.i.tude of the primary organic engine--the vegetable organism? We consider, here, in the first place, not intervening, but resulting phenomena.

The young leaf exposed to solar radiation is small at first, and the quant.i.ty of radiant energy it receives in unit of time cannot exceed that which falls upon its surface. But what is the effect of this energy? Not to produce a r.e.t.a.r.dative reaction, but an accelerative response: for, in the enlarging of the leaf by growth, the plant opens for itself new channels of supply.

If we refer to "the living protoplasm which, with its unknown molecular arrangement, is the only absolute test of the cell and of the organism in general,[1] we find a similar att.i.tude towards external sources of available energy. In the act of growth increased rate of a.s.similation is involved, so that there is an acceleration of change till a bulk of maximum activity is attained. The surface, finally, becomes too small for the absorption of energy adequate to sustain further increase of ma.s.s (Spencer[2]), and the acceleration ceases. The waste going on in the central parts is then just balanced by the renewal at the surface. By division, by spreading of the ma.s.s, by

[1] Claus, _Zoology_, p. 13.

[2] Geddes and Thomson, _The Evolution of s.e.x_, p. 220.

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out-flowing processes, the normal activity of growth may be restored. Till this moment nothing would be gained by any of these changes. One or other of them is now conducive to progressive absorption of energy by the organism, and one or other occurs, most generally the best of them, subdivision. Two units now exist; the total ma.s.s immediately on division is unaltered, but paths for the more abundant absorption of energy are laid open.

The encystment of the protoplasm (occurring under conditions upon which naturalists do not seem agreed[1]) is to all appearance protective from an unfavourable environment, but it is often a period of internal change as well, resulting in a segregation within the ma.s.s of numerous small units, followed by a breakup of the whole into these units. It is thus an extension of the basis of supply, and in an impoverished medium, where unit of surface is less active, is evidently the best means of preserving a condition of progress.

Thus, in the organism which forms the basis of all modes of life, a definite law of action is obeyed under various circ.u.mstances of reaction with the available energy of its environment.

Similarly, in the case of the more complex leaf, we see, not only in the phenomenon of growth, but in its extension in a flattened form, and in the orientation of greatest surface towards the source of energy, an att.i.tude towards

[1] However, "In no way comparable with death." Weismann, _Biological Memoirs_, p. 158.

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available energy causative of accelerated transfer. There is seemingly a principle at work, leading to the increase of organic activity.

Many other examples might be adduced. The gastrula stage in the development of embryos, where by inv.a.g.i.n.ation such an arrangement of the multiplying cells is secured as to offer the greatest possible surface consistent with a first division of labour; the provision of cilia for drawing upon the energy supplies of the medium; and more generally the specialisation of organs in the higher developments of life, may alike be regarded as efforts of the organism directed to the absorption of energy. When any particular organ becomes unavailing in the obtainment of supplies, the organ in the course of time becomes aborted or disappears.[1] On the other hand, when a too ready and liberal supply renders exertion and specialisation unnecessary, a similar abortion of functionless organs takes place. This is seen in the degraded members of certain parasites.

During certain epochs of geological history, the vegetable world developed enormously; in response probably to liberal supplies of carbon dioxide. A structural adaptation to the rich atmosphere occurred, such as was calculated to cooperate in rapidly consuming the supplies, and to this obedience to a law of progressive transfer of energy we owe the vast stores of energy now acc.u.mulated

[1] Claus, _Zoology_, p. 157

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in our coal fields. And when, further, we reflect that this store of energy had long since been dissipated into s.p.a.ce but for the intervention of the organism, we see definitely another factor in organic transfer of energy--a factor acting conservatively of energy, or antagonistically to dissipation.

The tendency of organized nature in the presence of unlimited supplies is to "run riot." This seems so universal a relation, that we are safe in seeing here cause and effect, and in drawing our conclusions as to the att.i.tude of the organism towards available energy. New species, when they come on the field of geological history, armed with fresh adaptations, irresistible till the slow defences of the subjected organisms are completed, attain enormous sizes under the stimulus of abundant supply, till finally, the environment, living and dead, reacts upon them with restraining influence. The exuberance of the organism in presence of energy is often so abundant as to lead by deprivation to its self-destruction. Thus the growth of bacteria is often controlled by their own waste products. A moment's consideration shows that such progressive activity denotes an accelerative att.i.tude on the part of the organism towards the transfer of energy into the organic material system. Finally, we are conscious in ourselves how, by use, our faculties are developed; and it is apparent that all such progressive developments must rest on actions which respond to supplies with fresh demands. Possibly in the present and ever-

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increasing consumption of inanimate power by civilised races, we see revealed the dynamic att.i.tude of the organism working through thought-processes.

Whether this be so or not, we find generally in organised nature causes at work which in some way lead to a progressive transfer of energy into the organic system. And we notice, too, that all is not spent, but both immediately in the growth of the individual, and ultimately in the multiplication of the species, there are actions a.s.sociated with vitality which r.e.t.a.r.d the dissipation of energy. We proceed to state the dynamical principles involved in these manifestations, which appear characteristic of the organism, as follows:--

_The transfer of energy into any animate material system is attended by effects conducive to the transfer, and r.e.t.a.r.dative of dissipation._

This statement is, I think, perfectly general. It has been in part advanced before, but from the organic more than the physical point of view. Thus, "hunger is an essential characteristic of living matter"; and again, "hunger is a dominant characteristic of living matter,"[1] are, in part, expressions of the statement.

If it be objected against the generality of the statement, that there are periods in the life of individuals when stagnation and decay make their appearance, we may answer, that