“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. * * * * *