sate for the radiations of luminous bodies have proved mere speculations. We know that the sun is radiating its heat into space; we do not know that space is returning this dissipated motion, either to the sun or to any other centre. We see planets and stars in various stages of their progress toward the stable state; we have no reason to believe that any are in the condition of transition from the stable to the unstable state.
The moon is supposed to have already passed through most, if not all, of its stages from the gaseous to the solid condition. Its atmosphere has been absorbed, its waters have retreated into its interior or perhaps been converted into solids, and all its visible activities have apparently ceased. If there still exist volcanic activities upon it, as certain observations seem to prove, they are probably the only ones, and are themselves declining. Doubtless there are other bodies in our solar system whose equilibration is even more complete than that of the moon—as, perhaps, some asteroids, or the satellites cf the outer planets. They have run their long cosmical course, and have arrived at last at the final state of complete, stable equilibrium. This state is the goal of the whole process of evolution. It must, therefore, be regarded, when viewed from this standpoint, as the state of greatest perfection in the life of every aggregate. Many of the heavenly bodies have certainly advanced far toward this condition, and all are undoubtedly approaching it. But where is the evidence that any have commenced to reverse this process? What star is suspected of being in a state of disintegration? Where in all the universe do we see solids turning into liquids, and liquids into gases? Where and how are the radiations emitted by concentrating bodies being harvested again, and applied to the disintegration of completely integrated matter? In a word, amid all these manifest proofs of evolution, what proof exists of dissolution regarded as a cosmical process? We are bound to confess that there is none. We are justified in its assumption on a priori grounds alone, if at all. The law of the conservation of energy, now so well established in all the departments of physics, must be theoretically extended to the mechanics of space. This law is only another expression for the indestructibility of motion. If no motion can be destroyed, the same quantity must always exist in the universe. And as motion is necessarily nothing more than the local change of material atoms, all the solar and astral radiations must continue for all time to affect the same quantity of matter to the same extent. Hence these radiations cannot be wholly lost. Still, all this may be true, without affecting the question of the dissolution of worlds. The minute fraction of the sun's heat which is intercepted and absorbed by the different bodies of the solar system is utterly insufficient to ever effect their disintegration; and it is continually diminishing as the sun itself approaches the term of its existence: a fortiori, no such results can ever be produced by any of the more remote
