COSMIC PHILOSOPHY 



the solar system, otherwise apparently inexpli- 

 cable, are beautifully explained by the theory 

 of nebular genesis. Let us first consider a case 

 which would appear to be an obstacle, not only 

 to this, but to any other framable theory. We 

 have already hinted that Uranus, while revolv- 

 ing in the same direction with the other planets, 

 has a backward rotation, so that to an observer 

 placed upon Uranus the sun would seem to 

 rise in the west and set in the east. His moons 

 revolve about him in the same retrograde direc- 

 tion ; and his axis, instead of standing at a great 

 angle to his orbit-plane, as is the case with all 

 the nearer planets, lies down almost upon the 

 orbit -plane. It has been asserted that these 

 peculiarities are also manifested by Neptune 

 — though our opportunities for observing the 

 latter planet are so few that this point cannot 

 yet be regarded as well established. Why now 

 should such exceptional phenomena be mani- 

 fested in the case of either or both of these out- 

 ermost planets? In his essay on the Nebular 

 Hypothesis, Mr. Spencer has shown that these 

 phenomena may be explained by a reference to 

 the shape of the rings from which the outermost 

 planets were formed. When the solar nebula 

 was so large as to fill the orbit of Neptune, its 

 rotation must have been slower, and its figure 

 consequently- less oblate, than at later stages of 

 contraction. Now the ring detached from a very 

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