THE BIRTH AND DEATH OF WORLDS 413 



would then be thrown off as a revolving ring. This process 

 would be repeated as the contraction continued, with the result 

 of forming a series of such rings. The formerly continuous 

 mass would then present some such an appearance as Saturn 

 does now. 



In each of these zones the denser materials, if they existed, 

 would in cooling condense first ; the zone would then be com- 

 posed of mixed elements, partly solid, partly nebulous. If a 

 sufficient nucleus were formed, this would gradually gather 

 together unto itself all the materials of the ring, resulting in 

 the formation of a fiery globe. This in further cooling would 

 present us with the planets which we see and upon one of which 

 we live. 



It needs be said that in the theory of Laplace, as in the 

 ideas of Kant, there was much that was purely speculative. 

 Moreover, the hypothesis as framed by Laplace is open to as 

 serious objections as was that of Kant. It is not at all clear 

 that this cooling and contraction of the nebulous mass would 

 produce such zones as Laplace supposed. It was pointed out 

 that with increasing rotation the mass was just as likely to throw 

 off little wisps of vapour as a vast zone. Moreover, as Newcomb 

 has pointed out, in this theory the outer planets would have 

 been formed first. There seems to be no evidence that such 

 was the case. It is likely that the outermost planets are still 

 in a much more fluid condition than some of the inner bodies 

 like the earth. Finally, the discovery of the rotation of the 

 satellites of Uranus, in opposite direction to that of the other 

 planets and satellites, quite disrupted the idea of perfect uni- 

 formity of motion. These and perhaps other considerations, 

 pointed out by various writers, forbade acceptance of the hypo- 

 thesis in its primitive form. 



It needs be said, too, that the theory was never presented by 

 Laplace as a finality. He gives it, he says, " with that distrust 

 with which we must regard all that is not the result of observa- 

 tion and of calculation." It was a conception of grandeur ; 

 it had a very considerable degree of probability in spite of its 

 difficulties ; it was, moreover, in its broader outlines the only 

 thinkable process by which our system could have arisen. But 

 had no new evidence been adduced in its favour, it would pro- 

 bably have remained an interesting, not to say fascinating, 

 speculation and nothing more. 



