PLANETARY EVOLUTION 



a parallel phenomenon. But in the solar sys- 

 tem there is a conspicuous break in the uni- 

 formity' of succession ; and this break curiously 

 occurs just at the place where, according to the 

 most plausible supposition, there was an arrest 

 or failure in the normal formation of a planet. 

 I have partially succeeded in tracing this arrest 

 or failure to the immediate effects wrought by 

 the mere proximity and gigantic size of the 

 planet just preceding in the order of detach- 

 ment. Whether it can be shown that this cause, 

 which well-nigh accounts for one of this group 

 of phenomena, will account in some analogous 

 way for the whole group — whether it can be 

 shown that the detachment of this gigantic 

 mass may have altered the dynamic relations 

 of the central spheroid in such a way as to re- 

 duce to a minimum its power of eliminating fur- 

 ther rings, I will not pretend to say. It seems 

 to me better to leave the problem with this 

 clear and definite statement, rather than to en- 

 cumber it with hypothetical explanations which 

 are quite likely to prove purely gratuitous. Of 

 the various explanations which have occurred 

 to me, none seem at all satisfactory ; and I will 

 gladly resign, into abler hands, the task of 

 solving the problem. What we may regard, 

 however, as fairly established, is this, — that 

 while, after the formation of Jupiter, the de- 

 tachment of rings followed the same law of pro- 

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