2. _How nebulæ occupy so much space._—It accounts for the enormous _space_ occupied by nebulæ. It may be objected that, enormous as would be the original temperature of the solar system produced by the primeval collision, it would nevertheless be insufficient to expand the mass, against gravity, to such an extent that it would occupy the entire space included within the orbit of Neptune. But it will be perceived, from what has already been stated regarding the dispersion of the materials before they had sufficient time to assume the gaseous condition, that this dispersion was the main cause of the gaseous nebula coming to occupy so much space. And, to go farther back, it was the suddenness and almost instantaneity with which the mass would receive the entire store of energy, before it had time to assume even the molten, not to say the gaseous, condition, which led to tremendous explosions, followed by a wide dispersion of materials. 3. _Why nebulæ are of such varied shapes._—Although the dispersion of the materials would be in all directions, it would, according to the law of probability, very rarely take place uniformly in every direction. There would generally be a greater amount of dispersion in some directions than in others, and the materials would thus be carried along various lines and to diverse distances; and, although gravity would tend to bring the widely scattered materials ultimately together into one or more spherical masses, yet, owing to the exceedingly rarified condition of the gaseous mass, the nebulæ would change form but slowly. 4. _Broken fragments in a gaseous mass of an excessively high temperature the first stage of a nebula._—From what has already been shown, it will be seen that after the colliding of the two dark bodies the first condition of the resulting nebula would be an enormous space occupied by broken fragments of all sizes dashing against each other with tremendous velocities, like the molecules in a perfect gas. All the interspaces between those fragments would be entirely filled with a gaseous mass, which, at its earliest stages at least, as in the case of the solar nebula, would have a temperature probably more than one hundred thousand times that of the voltaic arc. Whether such a mass would be visible is a point which can hardly be determined, as we can have no experience on earth of a gas at such a temperature.