TRANSLATOR'S INTRODUCTION Ixxxi 



account for the heat. Kant supposes annular zones 

 of freely revolving nebulous matter to gather 

 together by attraction during condensation of the 

 Nebula. Laplace supposes rings left behind by the 

 cooling of the Nebula to agglomerate, in the same 

 way as Kant had done. While both appeal to the 

 rings of Saturn as an example of the hypothesis, 

 neither explains satisfactorily why the planetary 

 rings are not as stable as those of Saturn. Both 

 assert that the positive rotation of the planets is a 

 necessary consequence of agglomeration, but neither 

 is sufficiently explicit. The genesis of satellites is 

 for each of them a repetition on a small scale of the 

 formation of the system. Each refers comets to 

 nebulous matter more distant than the planets, but 

 Kant thought it merely the superficial portion of 

 the Solar Nebula/ 'Comets were regarded by 

 Laplace as little Nebulas formed outside of the 

 Solar System, while Kant considered them as 

 arising in the extreme portions of the Solar 

 Nebula.' l 



1 We may also quote, as relevant here, what Mr. Becker says of 

 Lord Kelvin's view : ' While Laplace assigns no cause for the heat 

 which he ascribes to his nebula, Lord Kelvin goes further back and 

 supposes a cold Nebula consisting of separate atoms or of meteoric 

 stones initially possessed of a resultant moment of momentum equal or 

 superior to that of the solar system. Collision at the centre will reduce 

 them to a vapour, which then expanding far beyond Neptune's orbit 

 will give a nebula such as Laplace postulates. Thus Kelvin goes back 

 to the same initial condition as Kant, excepting that Kant endeavoured 

 (of course vainly) to develop a moment of momentum for his system 

 from collisions.' Lc. p. 108. 



