We may now say that we have taken our nebula to pieces, with the exception of the parts belonging to the satellites of those planets which have them; which would only be a tiresome repetition of what we have done for each principal member of the system, provided we had the necessary data, which we have not; and have thus acquired a certain amount of knowledge of the primitive conditions of each one of them. But we have still to examine into and draw conclusions from what we have seen and learned during the operation; which in some points, differ very much from our notions, formed from what we had previously read on the subject. CHAPTER VI. PAGE 108 Analysis continued. Excessive heat of nebula involved condensation only at the surface. Proof that this was Laplace's idea. 109 Noteworthy that some astronomers still believe in excessive heat. 110 Interdependence of temperature and pressure in gases and vapours. Collisions of atoms the source of heat. 110 Conditions on which a nebula can be incandescent. Sir Robert Ball. 112 No proper explanation yet given of incandescent or glowing gas. 115 How matter was thrown off, or abandoned by the Jovian nebula. 116 Division into rings of matter thrown off determined during contraction. 117 How direct rotary motion was determined by friction and collisions of particles. 118 Saturn's rings going through the same process. Left to show process. 120 Form gradually assumed by nebulæ. Cause of Saturn's square-shouldered appearance. 120 A lens-shaped nebula could not be formed by surface condensation. 121 Retrograde rotary motion of Neptune and Uranus, and revolution of their satellites recognised by Laplace as possible. 123 Satellites of Mars. Rapid revolution of inner one may be accounted for. 124 Laplace's proportion of 4000 millions not reduced but enormously increased by discoveries of this century. ANALYSIS OF THE NEBULAR HYPOTHESIS--_continued_.