26 A Century of Science 



ing that as a generalization of embryology Baer s 

 law needs important emendations, and he went on to 

 prove that, as thus rectified, the law of the develop 

 ment of an ovum is the law which covers the evolu 

 tion of our planetary system, and of life upon the 

 earth s surface in all its myriad manifestations. 

 In Spencer s hands, the time-honoured Nebular 

 Theory propounded by Immanuel Kant in 1755, 

 the earliest of all scientific theories of evolution, 

 took on fresh life and meaning ; and at the same 

 time the theories of Lamarck and Darwin as to 

 organic evolution were worked up along with his 

 own profound generalization of the evolution of 

 mind into one coherent and majestic whole. Man 

 kind have reason to be grateful that the promise 

 of that daring prospectus which so charmed and 

 dazzled us in 1860 is at last fulfilled; that after 

 six-and-thirty years, despite all obstacles and dis 

 couragements, the Master s work is virtually done. 

 Such a synthesis could not have been achieved, 

 nor even attempted, without the extraordinary 

 expansion of molecular physics that marked the 

 first half of the nineteenth century. When Priest 

 ley discovered oxygen, the undulatory theory of 

 light, the basis of all modern physics, had not been 

 established. It had indeed been propounded as 

 long ago as 1678 by the illustrious Christian Huy- 



