iSular and Planetary Erohition. 



61 



Kow, certain objections have been made to the nebular 

 theory, the most important of -whicli is based upon the di- 

 rection of the rotation of the two outermost phxnetsand their 

 satellites. The satellites of the inner series of planets, from 

 Mercury to Saturn, inclusive, revolve as the planets do, from 

 west to east. Those of Uranus, however, revolve nearly at 



Rotation 

 of the 



OUtlT 



plaiK'ts, 



and 



retro.irrade 



motion 



of tlie 



satellites. 



Rotation 

 of the 

 inner 



planets, 



and 



direct 



motion 



of the 



satellites. 



Fig. 6. Motion of planets and satellites if formed simultaneously, as by Faye's 



hypothesis. 



right angles with the plane of rotation of the planet, while 

 those of Neptune revolve in a reverse direction. This would 

 at first apj)ear to be a serious objection to the theory ; but 

 recently the French astronomer, Faye, has propounded an 

 hypothesis which explains this apparent anomaly. (See 

 Figures 5 and 6, above and on the opposite page.) Faye's 



