215. Sun and planet, as individual spheres, have also their own individual gravity. The æther therefore must exist otherwise than in the universal sphere. The next change of the æther is _condensation_, more intense gravity, because it becomes more individual, centre and periphery approximate more closely to each other. The heavenly bodies must contain more matter, more æther in an equal space than the terrestrial globe. 216. The heavenly bodies have obtained their matter nowhere else than out of the primary matter, the æther; they are condensed æther. The heavenly bodies of a solar system have derived their mass out of the æther, which is found within the confines of this solar system. The matter of the heavenly bodies was thus previous to its coagulation strewn in the space of the solar system, and has been by so much the rarer, as the space of the solar system is larger than the volume of all the planets together with the sun. It admits therefore of being calculated how much rarer the æther is than e. g. water. 217. The æther is therefore not absolutely imponderable, but only so in relation to the heavenly bodies. Light and heat are therefore ponderose substances, though they are not ponderable. 218. The separation of the æther into central and peripheric mass has happened according to the laws of light, and thus according to the centroperipheric primary antagonism. As a consequence of this, only _one_ central body can originate in a solar system; the mass of the periphery can, however, divide into several, and must divide into as many as the light has moments of operation; of this we shall speak for the first time in treating of colours. 219. The matter of the periphery can be condensed by light into no other form than that of a _hollow_ globe around the sun. The planets are originally concentric _hollow globes_, in the midst of which the sun is formed. There are several hollow globes, because the light has several points of contraction at certain distances from the sun. 220. The number of hollow planetary globes is a definite one, and it is not an arbitrary matter how many of them originate. 221. The matter of such a hollow globe of æther is still, however, rarer by so much than the present planetary mass, as that of our earth would be rarer if it were to form a hollow globe around the sun, about as thick only as from the earth to the moon. 222. This hollow globe rotates with the sun, because the whole globe of æther, which fills out the space of the subsequent solar system, rotates; therefore everything necessarily tends in one direction. 223. These hollow planetary globes, on account of the rarity of their mass, their rotation, and the greater tension of light, could not subsist in the equatorial plane of the solar system, but coagulate together in equatorial rings about the centre of the whole system. The planetary foetuses are only _solar rings_, which rotate with the sun.