RECENT COSMOGONIES 261 



By their collisions with the masses of gases which they en- 

 counter, they (the dust particles) gradually assume a circular 

 movement about the axis of rotation of the nebula. In this ro- 

 tation they condense portions of the gases on their surface, and 

 hence acquire a high temperature which they soon lose again, 

 however, owing to the comparatively rapid radiation. 



Our considerations lead to the conclusion that there is rotat- 

 ing about the central body of the nebula an immense mass of 

 gas, and that, outside this mass, there are other centres of con- 

 densation moving about the central body together with the masses 

 of gas concentrated about them. Owing to the friction between 

 the immigrated masses and the original mass of gas which cir- 

 culated in the equatorial plane of the central body, all these 

 masses will keep near the equatorial plane, which will therefore 

 deviate little from the ecliptic. We thus obtain a proper plane- 

 tary system, in which the planets are surrounded by colossal 

 spheres of gas like the stars in the Pleiades. If now, the planets 

 have very small mass by comparison with the central body as in 

 our solar system they will be cooled at an infinitely faster rate 

 than the sun. The gaseous masses will soon shrink, and the 

 periods of rotation will be shortened; but for those planets, at 

 least, which are situated near the centre, these periods will orig- 

 inally differ little from the rotation of the central body. The 

 dimensions of the central body will always be very large, and 

 the planets circulating about it will produce very strong tidal ef- 

 fects in its mass. Its period of rotation will be shortened, while 

 the orbital rotation of the planets will tend to become lengthened. 

 Thus the equilibrium is disturbed; it is re-established again, be- 

 cause the planet is, so to say, lifted away from the sun, as G. H. 

 Darwin has so ingeniously shown with regard to the moon and 

 the earth. Similar relations will prevail in the neighborhood of 

 those planets which will thus become provided with moons. 

 Hence we understand the peculiar fact that all the planets move 

 almost in the same plane, the so-called ecliptic, and in approxi- 

 mately circular orbits; that they all move in the same direction, 

 and that they have the same direction of rotation in common with 

 their moons and with the central body, the sun. It is only the 

 outermost planets, like Uranus and Neptune, in whose cases the 

 tidal effects were not of much consequence, that form exceptions 

 to this rule. 



Our author's second aim is to point out what he re- 

 gards as Nature's method of self -restoration by revers- 

 ing, as it were, the thermal hour glass and starting the 

 heat current on the downward course once more. Quot- 

 ing Clausius' old maxim, "The energy of the universe is 



