62 Solar and Planetary Evolution. 



explanation rejects the theory of Laplace in part, and goes 

 back to that of Descartes, which assumes that the planetary 

 rings were produced by a vortical or whirlpool motion of the 

 original nebulous matter, and nearly simultaneously, instead 

 of by the successive separation of concentric rings. Suppos- 

 ing that the entire mass from which the planets are formed 

 revolves in one general direction as a whole, like a grind- 

 stone or wheel, it is evident that the outer edge of the 

 mass would rotate much faster than the inner portions. 

 This would also be true of a vortical ring formed within the 

 mass, and, when that ring broke up, as its outer edge would 

 tend to move faster than its inner edge this tendency would 

 be impressed upon the resulting spheroid, which consequent- 

 ly would rotate on its axis in the same direction in which 

 it moved around the sun. In this way, M. Faye thinks, the 

 inner planets received their impulse of rotation from west 

 to east. But before the rings of Neptune and Uranus (being 

 formed somewhat later than the others) condensed into 

 planets, the sun had attracted to itself nearly all the 

 matter not already formed into planets, and the rings, being 

 thus left separate, began to revolve, not as if they all 

 formed parts of one disk, but independently. Thereupon their 

 velocity varied inversely as their distance from the sun, 

 their outer edges tended to move more slowly than their 

 inner edges, and consequently the planets formed from them 

 rotated in the opposite direction to their revolution 

 around the sun. Of course the satellites formed from these 

 planets would revolve around their primaries in the same 

 direction in which the primaries rotated on their axes. 



Dr. Karl Braun, a German philosopher, has suggested an- 

 other theory of planetary evolution. He assumes that 

 throughout the original mass various centers of condensa- 

 tion were formed, which ultimately became planetary bodies, 

 revolving around the largest centre of condensation of all, 

 which was the sun. All these theories agree in assuming 

 that the original condition of the universe was that of a neb- 

 ular mass, and that suns and satellites were evolved from 

 it by the action of laws precisely similar to those which we 

 behold still active in this world in which we dwell. 



If, now, on looking at the starry heavens through the tel- 

 escope, we find nebulous masses in the same condition in 

 which we have supposed the sun and the earth to have form- 

 erly existed, it will go far to confirm the nebular hypothesis 



