PAGE 301 Former compromises taken up and begun to be fulfilled. 302 Estimates of the heat-power of the sun made only from gravitation hitherto. 303 Contraction and condensation of a nebula solid to the centre. Heat produced from attraction as well as by gravitation. 304 What quantity of heat is produced by a stone falling upon the earth. 305 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. 306 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. 307 In neither case could matter be brought to rest, but only retarded in motion. Different periods of rotation accounted for. 309 Table of different rates explained. 310 Heat produced by gravitation, attraction, and churning, not all constituents of the heat-power of the sun. 311 There can be no matter in the sun so dense as water. 312 The hollow part of the sun acting as a reservoir of gases, heat and pressure. 313 The behaviour of heat produced in the nebula, and its power. 314 How sun-spots are produced. 315 Cyclonic motions observed in sun-spots. Why not all in certain directions, and why only observed in a very few. 316 Cyclonic motions in prominences treated of. 317 Many other things might be explained, on some of which we do not dare to venture. Concluding observations.