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'has become unavailable, the history of the uni'verse 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.

conduction of heat.

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condition of any number of bodies at any future time so long as only thermal action take 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.'1

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 mole'cules, 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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Conception of Law.

difficulties. The idea of law as applied to the succession of external phenomena rests simply upon faith. We extend to the world, with necessary modifications, the idea of persistence which underlies the consciousness of 'self.' The conception of uniform repetition, of the permanence of that which is, is supplied by us from within to the results of observation. We are so constituted as to conclude with more or less confidence from a certain number of uninterrupted repetitions, that the series will continue. We are so constituted as to extend this form of conclusion boldly even where the result depends upon the combination of many conditions which may severally fail of fulfilment. And in affirming that the succession in any case will be uniform, we do not simply affirm that the same antecedents will produce the same consequents-the opposite of which is inconceivable-but, which is a very a very different thing, that like antecedents will produce like consequents, and that in any particular case, we know all the antecedents, and know them fully, of which we cannot possibly be sure. Absolute accuracy in concrete things is unattainable. In the present order of things no antecedent can be the same in two cases. Nothing can actually recur. Every phenomenon is in its completeness unique. We may indeed be sure that if the

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