Comparison of the two forms, solid or hollow 269 The hollow centre form adopted. The jagged peaks left behind 272 The nebula assuming a spherical form. Shreds, masses,     crescents separated from one side 273 Probable form of interior of nebula. Compared with envelopes in heads of some comets 274 Reflections on the nebula being hollow. Opinions of others quoted 275 The matter of a sphere solid to the centre must be inert there 276 Further proofs of the nebula being hollow 277 How rotary motion was instituted 278 Such a nebula might take one of two forms 279 The form depending on the class of nebula. Planetary in the case of the solar system.     A similar conception of how rotary motion could be instituted 280
CHAPTER XVI.
  The sun's neighbours still exercise their attraction over him 282 Regions of greatest density in the 9 nebulæ dealt with; compared with the     orbits of the planets made from them 283 Results of comparison favourable to the theory 287 Differences of size in the planets have arisen from variations in the quantity     of matter accumulating on the nebulæ 289 Causes of the retrograde motions in Neptune, Uranus, and their satellites 290 Probable causes of the anomalous position of Neptune 292 Rises and falls in the densities and dimensions of the planets explained 293 The form of the nebulæ must have resembled a dumb-bell 295 More about rises and falls in densities 296 Reason why the Asteroid nebula was the least dense of the system; 297 Not necessary to revise the dimensions given to the 9 nebulæ 298 Causes of the anomalies in the dimensions, densities, etc., of the Earth and Venus 299 The strictly spherical form of the sun accounted for. But it may yet be varied 299 Repetition that a spherical body could not be made from a lens-shaped     nebula by attraction and condensation 300
CHAPTER XVII.
  Former compromises taken up and begun to be fulfilled 301 Estimates of the heat-power of the sun made only from gravitation hitherto 302 Contraction and condensation of a nebula solid to the centre.     Heat produced from attraction as well as by gravitation 303 What quantity of heat is produced by a stone falling upon the earth 304 Showing again that there is a difference between attraction and gravitation 305 Contraction and condensation of a hollow-sphere nebula, in the same manner as the solid one 305 Differences of rotation would be greater in a hollow nebula; because a great deal of   the matter would be almost motionless in a solid sphere; 306 In neither case could matter be brought to rest, but only retarded in motion.     Different periods of rotation accounted for 307 Table of different rates explained 309 Heat produced by gravitation, attraction and churning, not all     constituents of the heat-power of the sun 310 There can be no matter in the sun so dense as water 311 The hollow part of the sun acting as a reservoir of     gases, heat and pressure 312 The behaviour of heat produced in the nebula, and its power 313 How sun-spots are produced 314 Cyclonic motions observed in sun-spots. Why not all in     certain directions, and why only observed in a very few 315 Cyclonic motions in prominences treated of 316 Many other things might be explained, on some of which we     do not dare to venture. Concluding observations 317
CHAPTER XVIII.
  Return to the peaks abandoned by the original nebula. An idea of their number 319 Example of their dimensions. What was made out of them 320 What could be made from one of them 321 How it could be divided into comets and meteor swarms 322 An example given. How a comet may rotate on its axis. And what might be     explained thereby. Orbits and periods of revolution 323 Not ejected from planets. Their true origin 324 Study of the velocities in orbit of comets, and results thereof 326 How far comets may wander from the sun and return again 327 No reason why comets should wander from one sun to another. Confirmatory     of the description, in Chapter XV. of the sun's domains 328 Of the eternal evolution and involution of matter.     The atmosphere and corona of the sun 329 Partial analogy between it and the earth's atmosphere public@vhost@g@gutenberg@html@files@45356@[email protected]#Page_331" class="pginternal"