THE EVOLUTION OF THE WORLD. 245 



manner by " Newtonian laws " — that is, by mathe- 

 matical and physical laws — was made by Immanuel 

 Kant in the famous work of his youth (1755), General 

 History of the Earth and Theory of the Heavens. 

 Unfortunately, this distinguished and daring work 

 remained almost unknown for ninety years ; it was 

 only disinterred in 1845 by Alexander Humboldt in 

 the first volume of his Cosmos. In the meantime the 

 great French mathematician, Pierre Laplace, had 

 arrived independently at similar views to those of 

 Kant, and he gave them a mathematical foundation 

 in his Exposition du Systeme du Monde (1796). His 

 chief work, the Mecanique Celeste, appeared a hundred 

 years ago. The analogous features of the cosmogony 

 of Kant and Laplace consist, as is well known, in a 

 mechanical explanation of the movements of the 

 planets, and the conclusion which is drawn therefrom, 

 that all the cosmic bodies were formed originally by a 

 condensation of rotating nebulous spheres. This 

 " nebular hypothesis " has been much improved and 

 supplemented since, but it is still the best of all the 

 attempts to explain the origin of the world on 

 monistic and mechanical lines. It has recently been 

 strongly confirmed and enlarged by the theory that 

 this cosmogonic process did not simply take place 

 once, but is periodically repeated. While new cosmic 

 bodies arise and develop out of rotating masses of 

 nebula in some parts of the universe, in other parts 

 old, extinct, frigid suns come into collision, and are 

 once more reduced by the heat generated to the 

 condition of nebula?. 



Nearly all the older and the more recent cosmo- 

 gonies, including most of those which were inspired 

 by Kant and Laplace, started from the popular idea 



