284 SCIENTIFIC THOUGHT. 



The two lines of speculation, originated by Leibniz 

 and Kant as to the genesis of things on this earth and 

 in the universe, mark two distinct ways of approaching 

 the genetic problem. They were both isolated, and it 

 was not till well on in the course of our century that 

 they were again taken up and independently developed 

 the one by geologists, the other by physical astronomers. 

 They remained for a long time without mutual influence ; 

 till, within the last generation, they were brought to- 

 gether, their different results deduced, and a reconcilia- 

 tion attempted. To this I shall revert later on. Forty 

 > years after Kant, Laplace put forward his so-called 



Laplace. 



nebular hypothesis at the end of the popular exposition 

 which he gave of his mechanical theory of the heavens. 

 He apparently knew nothing of Kant's attempt, and his 

 views differ materially from those of Kant, in so much 

 as he assumes in the rotating nebular mass an attracting 

 nucleus from which, in the course of condensation through 

 attraction, the planetary rings and bodies were thrown 

 off as the centrifugal velocity balanced the attracting 

 forces. For a long time this sketch of a possible 

 genesis of the planetary system was paraded in popular 



work. The merits of Kant have only 

 been tardily recognised ; they were 

 unknown to Laplace, and only 

 imperfectly known to more recent 

 authorities, such as Helmholtz and 

 Lord Kelvin, who were fully pre- 

 pared to do him justice. Lord 

 Kelvin, in his Rede Lecture of 

 1866, refers to Kant as the first 

 to publish " any definite estimate 

 of the possible amount of the 

 diminution of rotatory velocity 

 experienced by the earth through 

 tidal friction " ( ' Pop. Lects. and 

 Addr.,' vol. ii. p. 65), and [in the I 



controversy which took place be- 

 tween him and Huxley on " Geo- 

 logical time " the theories of Kant 

 were frequently referred to. See 

 his lecture on "Geological Time," 

 1868 (loc. cit., p. 10, &c.) ; Huxley 

 on "Geological Reform," 1869 (re- 

 printed in ' Lay Sermons, 1 No. XI.) 

 The best account in the English 

 language of Kant's contributions 

 to cosmogony will be found in an 

 article by G. F. Becker in the 5th 

 vol., 4th series, of the 'American 

 Journal of Science,' 1898. 



