_Evolution of matter._—Our inquiries into stellar evolution do not, however, begin with the consideration of a gaseous nebula, or with swarms of meteorites. There was a pre-nebular evolution. The researches of Prout, Newlands, Mendelejeff, Meyer, Dumas, Clarke, Lockyer, Crookes, Brodie, Hunt, Graham, Deville, Berthelot, Stoney, Reynolds, Carnelley, Mills, and others, clearly show, I think, that the very matter forming this nebulous mass passed through a long anterior process of evolution. And not only the matter, but the very elements themselves constituting the matter, were evolved out of some prior condition of substance. I have already given at some length the views which have been advanced by several of our leading physicists and chemists on the evolution of the chemical elements, and on some of the bearings which these views have on stellar evolution. I shall now briefly refer to a point on which I venture to think the theory discussed in this volume seems to cast some additional light. If the elements were evolved out of a common source, there is, in order to this, one necessary condition, viz. an excessively high temperature; for the temperature must be above the point of the dissociation of all the chemical elements. “In the primal stage of the universe,” says Mr. Crookes, “before matter, as we now find it, was formed from the protyle, all was in an ultra-gaseous state, at a temperature inconceivably hotter than anything now existing in the visible universe; so high, indeed, that the chemical atoms could not yet have been formed, being still far above their dissociation point.” What, then, produced this excessive temperature in this supposed ultra-gaseous protyle? It could not have resulted from condensation by gravity. In condensation the heat increases as the condensation proceeds, because it is the condensation which produces the heat. But here the reverse must have been the case, for the ultra-gaseous mass was much hotter than the sun which was afterwards formed out of it. It was, according to Mr. Crookes, when this gaseous mass cooled down, so as to permit of its becoming converted into solid matter, that condensation into a sun could take place. Besides, was it not the excessive heat which produced the assumed ultra-gaseous condition? There is another difficulty besetting the theory that the primitive heat was derived from condensation by gravitation. Supposing we should assume it possible that the protyle could exist in this ultra-gaseous state without possessing temperature, and that it obtained its heat from condensation by gravity, then the fact of condensation taking place shows that the gas was not in a state of equilibrium. But the gas could not have remained stationary for a single moment without beginning to condense while in a condition of unstable equilibrium. We must therefore conclude that the gas must have been in some other condition than the gaseous state prior to condensation.