684 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



cause it to move in more open spirals, and thus enable it to get 



the inside track and overtake the other; or, at least, come so near 



to it as to attract it to itself and add it to its own mass. It was 



in this manner that I suppose that the rings Avere transformed into 



planets. 



Formation of Asteroids. 



"We can readil}' understand how, on this hypothesis, many of 

 the rings w^ere prevented from becoming planets. If one of the 

 rings were very massive, as in the case of that from which Jupiter 

 was formed, its attraction would prevent the next interior ring or 

 rino^s from undergoing the process already described as neces&ary 

 to the formation of a planet: that is to say, the spiral inwar^ 

 movement of the light matter in the outer part of the ring, Avould 

 be retarded, or entirely prevented, by the attraction of the mass- 

 ive exterior ring. This retardation Avould be the most likely to 

 take place in the interior parts of the system, where the rings 

 were very nai-row. We know that there is a zone of asteroids, 

 about one hundred millions of miles wide, in the interval between 

 the orbits of Jupiter and Mars. According to the theory here 

 advocated, there were originally fifteen rings in this interval. The 

 attraction of Jupiter has rendered them all asteroids: that is to 

 say, it has prevented the inward spiral movement which was 

 necessary to form each of them into a normal planet; and thus it 

 forced them to become aggregated into a greater number of plan- 

 etettes, which are abnormally smaller and nearer each other. Is 

 it not a strong presumptive proof of the truth of this theory that 

 the regular planets are all solitary? In no instance do we find 

 two moving in the same orbit, or the same zone; nor does an^^ 

 planet come near the orbit of another. If the rings had been 

 hrohtn up by any such accidents as the advocates of the nebular 

 hypothesis commonly imagine, the inevitable consequence w^ould 

 have been that, in some instances,, several planets, or fragments, 

 would have the same or nearly the same orbit. 



The following somewhat poetical account of the nebular hypothe- 

 sis is from Nichol's Cyclopedia of the Physical Sciences: 



"Has our reader walked in a mood of tranquil thought along the 

 side of a quiet river, whose .waving banks reflect a thousand cur- 

 rents, by the intermingling of which numerous dimples or whirl- 

 pools are produced — their easy course onl}^ marking the river's 

 stillness ? Has he folloAved these dimples as they pursue each 

 other in gambol, and watched the phenomenon of the near ap- 



