COSMOGONIES 117 



of mechanics — the law of conservation of moment 

 of momentum — the spinning body must spin faster 

 as it contracts, and thus at intervals, enough centri- 

 fugal force would be acquired to shed an equatorial 

 ring. The first ring would be thrown off where 

 Neptune spins in its outer orbit, the next would 

 account for Uranus, the next for Saturn, and so 

 on. By assuming the mist coherent so as to spin 

 " en masscy' Laplace was able to arrange that the 

 planets would spin on their axis in the right direc- 

 tion, not in the wrong direction, as Kant's planets 

 must have done. Unlike Kant, too, he did not 

 try to account for the initial rotation, but wisely 

 postulated it. 



It was a beautiful and plausible hypothesis, 

 beautiful in its simplicity, plausible in its explana- 

 tion, and to this day it has held the imagination of 

 mankind. What bolder and braver vision could 

 one have than the vision of this fiery mist rotating 

 in space and flinging off from its fringes the 

 flaming planets and the molten world ! What 

 could be more fascinating than the picture of the 

 beginning of the world as a belt round the waist 

 of the whirling sun ! 



But unfortunately the hypothesis is not mechani- 

 cally sound. If the sun and the planets were dis- 

 persed into space so as to fill an area bounded 

 by Neptune's orbit, they would form a gas so 



