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Dissipation of energy.

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'be made to do visible work." This work may be, under the conditions of our system, reduced to three kinds: the production of visible motion; the communication of heat from a hotter to a colder body; the transference of pressure in a system of constant volume from parts under great pressure to parts where the pressure is less. Now in each of these cases the doing of work is accompanied by a diminution of available energy. If, for example, visible motion is produced a certain amount of energy is lost by friction; or, in another aspect of the same case, if heat is transformed into motion, a part of the heat is forthwith diffused, and, when so diffused, it cannot afterwards be made effective to produce action. This diffusion therefore and generally this diminution of available energy can only have been continued for a limited time, for otherwise the end of a dead equilibrium would have been already reached.

'We have,' in other words, 'an irreversible 'process always going on, at a greater or less rate, in the universe. If therefore there was ever 'an instant at which the whole energy of the 'universe was available energy, that instant must 'have been the very first instant at which the universe began to exist. If there ever shall come a 'time at which the whole energy of the universe

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1 Prof. Clerk Maxwell, in Nature, Ix. pp. 198 ff.

'has become unavailable, the history of the universe will then have reached its close. During 'the whole intervening period the available energy 'has been diminishing and the unavailable in'creasing by a process as irresistible and as irre'versible as Time itself. The duration of the 'universe according to the present order of 'things is therefore essentially finite both a parte 'ante and a parte post.”1

In other words the assumed permanence of the existing laws of matter involves the consequence that the universe had a beginning within a measurable time; and if it be said that we have no right to assume the uniform action in the past of the laws which hold good now, that is to concede at once what is for us equivalent to a creative act.

The general law, which points to a historical beginning of the present order, finds expression in a particular case which is of great interest. The formula which represent the observed laws of the conduction of heat force us to take account at some point in the past of a creative act, that is of a discontinuity in the present order of phenomena. According to these formulæ it is possible to foresee the thermal

1 Prof. Clerk Maxwell, in Nature, ix. p. 200.

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conduction of heat.

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condition of any number of bodies at any future time so long as thermal action only takes place between them. If we go back, the same process may be reversed for a certain distance and the condition of the bodies may be referred to an earlier and continuous action of the same kind. But at last a limit is reached at which the condition of the bodies can no longer be explained in the same way. At this point then some change must have taken place in the relation of the bodies which marked essentially a fresh beginning. Again I will use the words of a master to describe the fact:

"The irreversible character of this process '[the dissipation of energy] is strikingly embodied ' in Fourier's theory of the conduction of heat, 'where the formulæ themselves indicate a possi'ble solution of all positive values of the time 'which continually tends to a uniform diffusion of 'heat. But if we attempt to ascend the stream 'of time by giving to its symbol continually 'diminishing values, we are led up to a state of 'things in which the formula has what is called a 'critical value; and if we inquire into the state of 'things the instant before, we find that the 'formula becomes absurd. We thus arrive at 'the conception of a state of things which cannot 'be conceived as the physical result of a previous

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'state of things, and we find that this critical condition actually existed at an epoch not in the 'utmost depths of a past eternity but separated 'from the present time by a finite interval."

Thus the principle of the dissipation of energy suggests distinctly both a beginning and an end of the present order. It suggests also some creative action, so far at least as to make it clear that the laws which we can trace now will not allow us to suppose that the order which they express has existed for ever. Physicists have gone yet farther. If matter is pursued to its ultimate form, we find at last, according to the most competent judgment, molecules incapable of subdivision without change of substance, which are absolutely similar for each substance. A molecule of hydrogen, for example, has exactly the same weight, the same period of vibration, the same properties in every respect, whether it be found in the Earth or in the Sun or in Sirius. The relations of the parts and movements of the planetary systems may and do change, but these molecules--the foundation stones of the material universe-remain unbroken and unworn.' 'No theory of evolution can be

1 Clerk Maxwell, Address at Brit. Assoc., Liverpool, Sept. 1870. (Nature, II. pp. 421 f.)

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'formed to account for the similarity of molecules, for evolution necessarily implies continuous 'change, and the molecule is incapable of growth or decay, of generation or destruction. None of 'the processes of Nature, since the time when 'Nature began, have produced the slightest dif'ference in the properties of any molecule. We 'are therefore unable to ascribe either the exist'ence of the molecules or the identity of their properties to the operation of any of the causes 'which we call natural....The exact quality of 'each molecule...precludes the idea of its being 'eternal and self-existent.' We cannot, in other words, represent to ourselves the ground of this final and immutable similarity in any other way than as a result of a definite creative will.

So much at least is clear, that the mystery of creation is not introduced by religion. It is forced upon us by the world itself, if we look steadily upon the world. And no mystery can be greater than this inevitable mystery.

Again: if we turn from the conception of becoming to that of being, from creation to orderly existence, we find ourselves confronted with new

1 Nature, VIII. p. 441. (Molecules, a Lecture delivered at Bradford, 1873, by J. Clerk Maxwell. Compare Introductory Lecture on Experimental Physics, pp. 21 ff.)

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