The Evolution of the Sciences 



equilibrium and movement of bodies and still 

 owes to physics all its subsequent progress, 

 as regards, for example, the impact of bodies 

 and friction. If at the present day even its 

 principles seem to be undergoing transformation 

 to such an extent that the notion of mass is 

 losing the exact meaning which it had previ- 

 ously/ the cause must be sought in the recent 

 researches upon radio-active substances. 

 Astronomy on its side, after being satisfied 

 for long with the experimental laws of gravita- 

 tion, has taken a new development, laying 

 under contribution all the resources of modern 

 physics for the study of celestial spaces, and 

 gravitation itself has become one of its most 

 pressing problems. 



Geology no longer limits itself to the study 

 of rocks and formations. To reconstitute the 

 history of the globe, to determine the constitu- 

 tion of its deepest strata, it must make appeal 

 to our ever-deepening knowledge of the laws 

 which rule matter, heat and magnetism. It is 

 the same with all the biological sciences. They 

 are face to face with the most redoubtable of 



1 Cf. Chap. " Does matter exist ? " 

 xii 



