194 THE LIMITATIONS OF SCIENCE 



worked mostly from the experimental side. With an 

 early tendency toward speculation, he wrote several 

 books which aimed to give a most concrete, and even 

 crude, picture, of natural phenomena. His present 

 position as executive head of a university has thrown 

 him into the practical affairs of life. And probably 

 his chief trait of mind is the belief that all things, from 

 engines to souls, are best considered as manifestations 

 of a luminiferous ether which has the characteristics 

 of a jelly. 



It will be best now to let Poincare state his ideas 

 regarding the scientific method in his own words : for 

 he has done so most lucidly and vividly. The quota- 

 tions are from Professor Halsted's authorized trans- 

 lations : 



" Experiment is the sole source of truth. It alone 

 can teach us anything new; it alone can give us cer- 

 tainty. But then, if experiment is everything, what 

 place will remain for mathematical physics? What 

 has experimental physics to do with such an aid, one 

 which seems useless and perhaps even dangerous ? And 

 yet mathematical physics exists, and has done unques- 

 tionable service. We have here a fact that must be 

 explained. The explanation is that merely to observe 

 is not enough. We must use our observations, and 

 to do that we must generalize. This is what men have 

 always done; only as the memory of past errors has 

 made them more and more careful, they have 



