Geology 



Under these circumstances the bulge ceased to shrink 

 towards the centre, while the main mass continued to do 

 so, and thus the bulge was left behind in the form of a 

 ring. 



This ring afterwards broke and formed a planet, 

 Neptune, which was itself rotating on its axis and was 

 at first gaseous. The process of ring-making was 

 repeated in the planet, the rings in this case giving rise 

 to satellites. 



Meantime the main mass of the nebula continued to 

 shrink towards its centre, leaving behind it ring after 

 ring, each one of which formed a planet, until eventually 

 the nucleus contracted and formed the Sun, which con- 

 tains by far the greater part of all the matter in the 

 system. 



Such, then, is Laplace's Nebular Hypothesis, and it 

 appears extremely probable that it was first suggested 

 to him by the rings of Saturn, which he looked upon as 

 satellites in course of formation. The fact that these 

 rings have been shown to consist of small satellites, and 

 not of gas, removes observational support for the theory, 

 and astronomers have recently stated that such a 

 mode of formation of the planets is quite out of accord 

 with all established laws of mechanics. 



So serious are these objections to Laplace's theory 

 that it appears to be no longer tenable, and therefore 

 some other must be sought. It may be mentioned that 

 the objections to Laplace's theory, which are chiefly of 

 a mathematical nature, apply equally to the meteoritic 

 hypothesis of Lockyer and its modifications. 



Under these circumstances Professor T. C. Cham- 

 berlin of Chicago brought forward the Planetesimal 



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