Ixxvi KANT'S UNIVERSAL NATURAL HISTORY 



of them all the following, by the competent hand of 

 Professor Newcomb, may be quoted as particularly 

 lucid in its statement of essential points : 



' Laplace was led to the Nebular hypothesis by considera- 

 tions very similar to those presented by Kant a few years 

 before. The remarkable uniformity among the directions of 

 rotation of the planets being something which could not 

 have been the result of chance, he sought to investigate its 

 probable cause. This cause, he thought, could be nothing 

 else than the atmosphere of the sun, which once extended so 

 far out as to fill all the space now occupied by the planets. 

 ' He does not, like Kant, begin with a chaos, out of which 

 order was slowly evolved by the play of attractive and 

 repulsive forces, but with the sun surrounded by its immense 

 fiery atmosphere. Knowing, from mechanical laws, that 

 the sum total of rotary motion, now seen in the planetary 

 system, must have been there from the beginning, he con- 

 ceives the immense vaporous mass forming the sun and his 

 atmosphere to have had a slow rotation on its axis. The 

 mass being intensely hot would slowly cool off, and as it did 

 so would contract towards the centre. As it contracted its 

 velocity of rotation would, in obedience to one of the funda- 

 mental laws of mechanics, constantly increase, so that a 

 time would arrive when, at the outer boundary of the mass, 

 the centrifugal force due to the rotation would counter- 

 balance the attractive force of the central mass. Then those 

 outer portions would be left behind as a revolving ring, 

 while the next inner portions would continue to contract 

 until, at their boundary, the centrifugal and attractive forces 

 would be again balanced, when a second ring would be left 

 behind, and so on. Thus, instead of a continuous atmos- 

 phere the sun would be surrounded by a series of concentric 

 revolving rings of vapour. 



