THE STORY OF NINETEENTH-CENTURY SCIENCE 



accustomed to philosophical speculation. But the ques- 

 tion early arose in the mind of Fresnel whether the 

 ether is not considerably affected by contact with the 

 particles of solids. Some of his experiments led him to 

 believe that a portion of the ether which penetrates 

 among the molecules of tangible matter is held captive, 

 so to speak, and made to move along with these par- 

 ticles. He spoke of such portions of the ether as 

 " bound " ether, in contradistinction to the great mass 

 of "free" ether. Half a century after Fresnel's death, 

 when the ether hypothesis had become an accepted len- 

 et of science, experiments were undertaken by Fizeau 

 in France, and by Maxwell in England, to ascertain 

 whether any portion of ether is really thus bound to 

 particles of matter ; but the results of the experiments 

 were negative, and the question is still undetermined. 



While the undulatory theory of light was still fighting 

 its way, another kind of evidence favoring the existence 

 of an ether was put forward by Michael Faraday, who, 

 in the course of his experiments in electrical and mag- 

 netic induction, was led more and more to perceive def- 

 inite lines or channels of force in the medium subject to 

 electro-magnetic influence. Faraday's mind, like that 

 of Newton and many other philosophers, rejected the 

 idea of action at a distance, and he felt convinced that 

 the phenomena of magnetism and of electric induction 

 told strongly for the existence of an invisible plenum 

 everywhere in space, which might very probably be 

 the same plenum that carried the undulations of light 

 and radiant heat. 



Then, about the middle of the century, came that final 

 revolution of thought regarding the nature of energy 

 which we have already outlined in the preceding chap- 



234 



