II THE PROGRESS OF SCIENCE 101 



ditions, which no one could deny to be a matter 

 of fact, when his attention was drawn to the evi- 

 dence ; and the occurrence of great geological 

 changes, which also was matter of fact ; could be 

 used as the only necessary postulates of a theory 

 of the evolution of plants and animals which, even 

 if not, at once, competent to explain all the known 

 facts of biological science, could not be shown 

 to be inconsistent with any. So far as biology 

 is concerned, the publication of the " Origin of 

 Species," for the first time, put the doctrine of 

 evolution, in its application to living things, upon 

 a sound scientific foundation. It became an in- 

 strument of investigation, and in no hands did it 

 prove more brilliantly profitable than in those of 

 Darwin himself. His publications on the effects 

 of domestication in plants and animals, on the in- 

 fluence of cross-fertilisation, on flowers as organs 

 for effecting such fertilisation, on insectivorous 

 plants, on the motions of plants, pointed out the 

 routes of exploration which have since been fol- 

 lowed by hosts of inquirers, to the great profit of 

 science. 



Darwin found the biological world a more than 

 sufficient field for even his great powers, and left 

 the cosmical part of the doctrine to others. Not 

 much has been added to the nebular hypothesis, 

 since the time of Laplace, except that the attempt 

 to show (against that hypothesis) that all nebulas 

 are star clusters, has been met by the spectroscopic 



