latter.

We arrive at the conclusion that the sum of the two, the potential and the kinetic, throughout the

The changes

Universe must always be the same. of nature do but pass energy from one form to another. And hence arises at first sight the idea that the Universe may be eternal. Matter, its substance, is indestructible. Energy, its great agent of change, is indestructible. Can, then, its events be a perpetually recurring cycle? Here come in the considerations which constitute the theological argument, for whose examination I have been endeavouring to prepare my reader. It is maintained that, upon a comprehensive review of the changes going on in the Universe, it is clearly seen that those changes on the whole constantly pass its energy into forms less and less fitted to carry on the work of such a world as ours; that the general progress is to mutual rest, coldness, death; and that consequently the great machine cannot have been going for ever, or this state of mutual rest, coldness, and death would have supervened. This tendency of things is called the dissipation of energy. How it is thought to be shown I will try to explain more particularly.

The matter of the Universe known to us may be divided into an ether of extreme tenuity pervading all space, and the matter which composes the sun, stars, planets, satellites, meteors, comets, nebulæ, generally the heavenly bodies, including our earth.

F

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No doubt there is in many of these latter matter of extreme rarity, as in the comets and the nebula. But it is to be distinguished from the ether. We will here speak of it under the general name 'cosmical bodies.' The main peculiarity which tends to destroy the present state of things is this, that the energy, either potential or kinetic, in the cosmical bodies, constantly tends to diffuse itself, either as light or heat, or in some kindred form, through the great ocean of ether; and when it is so diffused, there does not seem, so far as we can see, to be any adequate agency for again collecting it in the cosmical bodies, and so carrying on the work of a world like ours.

For simplicity's sake we will consider the solar system first. If we observe the radiation of heat from its members, we see at once one great cause of the change in question. So long So long as a cosmical body is hot enough to be fluid, this radiation goes on at a tremendous pace. The sun, for instance,1 it has been computed, radiates every year a sufficient quantity of heat to boil sixty thousand billions of billions of pounds of ice-cold water. Professor Tyndall, in his work Heat a Mode of Motion,' has given some illustrations to help us to form some idea of this inconceivable radiation. It would in one hour melt a coat of ice all over the sun

1 Sir W. Thomson's article on the 'Age of the Sun's Heat,' Macmillan's Magazine, March 1862.

2,400 feet thick. It would boil in the same time 700,000 million cubic miles of ice-cold water. It would equal the heat given out by burning in one hour a layer of coal over the sun's surface 10 feet thick. When the body is so far cooled that its surface becomes solid, the radiation is very greatly reduced, but not altogether destroyed. Again we observe another source of dissipation. The ether resists the motion of all the planetary bodies, and this resistance tends to abstract a portion of their motion, and convert it into diffused heat. It also tends ultimately to make the planets, the satellites, and the minor bodies, all fall into the sun. Of the retardation it is true that we can at present discern only the faintest traces-an effect upon a single comet. But the cooling has evidently made great progress. The form of the earth, for instance, shows that she was once a fluid mass. Our most probable conjecture as to the origin of the solar system is that its larger members have been formed either by the condensation of a nebulous vapour, or by the falling together of smaller bodies, even as meteors still fall on the surface of the earth. The consequent destruction of motion accounts for the originally heated state of the bodies of our system. But so great is the expenditure of heat from the sun, that Sir W. Thomson1 has calculated 1 See article just named.

that the above theory will not account, at the very most, for an amount of solar heat able to support that expenditure for more than 100 millions of years, probably very much less. We conclude, then, that there is a constant tendency in our system to burn out, so to speak. The falling in of the planets and satellites might keep up the sun's heat for a time, but only for a time.

No

We see, then, the prospect before our system. At some distant time-a time enormously distant, I allow, as we reckon duration-the sun and the planets, and all his other dependents, will have become a vast agglomeration of cold dark lifeless matter. It may be said that the falling in of the small bodies called meteors gathered in from the space through which the system is passing may retard the approach of this consummation. doubt it will, but only for a time. Still further, a possible collision between our sun and some other great cosmical body may reverse the process altogether. In such a case a prodigious amount of heat might be evolved. The sun, even if grown partially solid, might be vaporised. Again, condensation might set in, and new planets might be formed. In fact, we might have the genesis and history of a new system. All this is conceivable, nay actually probable. But it would only lead to a repetition of the same process of cooling and

accumulation. It is clear that the same agencies which we expect to destroy the solar system in the long lapse of time, would also in a much greater lapse of time destroy that more stupendous system of which it is a part. Our argument requires that we should extend this view to the entire physical Universe. It pronounces that the Universe tends ultimately to lose its available energies, to arrive at a condition in which the cosmical matter is accumulated in one unchanging mass, and it argues accordingly that the Universe cannot have existed from eternity under its present code of laws, or the catastrophe just described would have supervened already. In other words, the existing state of things cannot have been derived from other pre-existing states, through an infinite period of past time, according to existing laws. Hence we must assume an epoch at which these laws had a beginning. Metaphysically speaking, such a beginning is not identical with a creation, because this latter word is generally understood to mean the calling into existence of the substance of matter. But still such a beginning of the present order of nature does suggest origination in a divine will.

In this sketch of the argument from the dissipation of energy, I have endeavoured to describe the actual process by which that principle mainly

takes effect upon the Universe at large. It seemed

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