THE ASTEROIDS BETWEEN MARS AND JUPITER. 371 



millions of miles, could not have originated, as supposed by Laplace, 

 in a single nebulcus zone the different parts of which revolved with the 

 same angular velocity. 



The process of planetary separation, both exterior and interior to the 

 zone of asteriods, was probably similar to that indicated above. The 

 nebular hypothesis, in this view, assigns an obvious cause for the origi- 

 nal formation of planetary nuclei in such positions that their periods 

 would be nearly commensurable with that of the disturbing body. As 

 these nuclei would receive accretions of matter from portions of space 

 both exterior and interior to their respective orbits, their distances from 

 the central body, during their planetary growth, would not be liable to 

 great variation. 



If anything can be inferred from the similarity of adjacent orbits 

 pointed out on a previous page, it is that the minor planets so related 

 were derived from the same nebulous ring or mass, and that the pertur- 

 bations to w hich they have been liable have not yet wholly effaced this 

 evidence of a common origin. 



