THE BIRTH AND DEATH OF WORLDS 411 



that of Kant ; in the main it was broadly the same. In the 

 third edition of the Exposition, published twelve years later, 

 he made some slight additions, and it is on the basis of these 

 rather than his first sketch that it has become customary to 

 speak of him as the author of the Nebular Hypothesis. Its 

 originator he certainly was not. By that time (1808) the idea 

 of nebular origins was common property. 



What there was in Laplace's exposition of the theory 

 original to him is so brief that it may be stated in his own 

 words. He reviews the calculations of Daniel Bernouilli, with- 

 out, however, any reference to the latter or to his papers. 

 The number of planetary motions had been somewhat increased 

 by the discovery of Uranus and numerous satellites ; he con- 

 cludes that the chances then are 137,000 millions to one that 

 the system did not arise in any fortuitous way. He dismisses 

 the conjectures of Buffon as unable to explain four out of five 

 of the principal planetary phenomena, then proceeds : 



" This hypothesis, being very far from satisfying the re- 

 quired conditions, let us see if it is possible to rise to their true 

 cause. Whatever be its nature, since it has produced or im- 

 pressed the movements of the planets and the satellites, it 

 must have once embraced all of these bodies ; and considering 

 the prodigious distance which separates them, it can only have 

 been a fluid of immense extent. In order to have given them 

 a movement almost circular around the sun, and in the same 

 direction, it is necessary that this fluid must have once sur- 

 rounded the sun like an atmosphere. Consideration of the 

 planetary movements leads us to believe that, by virtue of 

 an excessive heat, the atmosphere of the sun once extended 

 beyond the orbits of all the planets, and that it has successively 

 contracted up to its present limits ; this might have taken 

 place by reason of causes similar to those which occasioned 

 the brilliant luminescence through several months of the famous 

 star that was seen of a sudden in 1572, in the constellation of 

 Cassiopeia. 



" The great excentricity of the orbits of the comets leads 

 to the same result. It indicates evidently the disappearance 

 of a large number of orbits less excentric. This in turn supposes 

 an atmosphere around the sun which extended beyond the 

 perihelion of observable comets, and which in destroying the 



