THE ETHER 107 



naturally arose, could matter attract matter across 

 space unless there was some substance between 

 connecting them ? Newton thought it could not. 

 In his famous third letter to Bentley he wrote : 

 " It is inconceivable that inanimate brute matter 

 should, without the mediation of something else 

 which is not material, operate upon and affect other 

 matter without mutual contact, as it must do if 

 gravitation, in the sense of Epicurus, be essential 

 and inherent in it. And this is the reason why I 

 desired you would not ascribe innate gravity to me. 

 That gravity should be innate^ inherent and essential 

 to matter^ so that one body may act upon another at a 

 distance through a vacuum without the mediation of 

 anything else by and through which their action may 

 be conveyed from one to another^ is so great an 

 absurdity that I believe no man who has in philosophic 

 matters a competent faculty of thinking can ever fall 

 into itr 



The impossibility, then, of conceiving " actio in 

 distans," of believing that one body can act on 

 another body at a distance without material media- 

 tion, gave origin to the hypothesis of ether. 

 Philosophically, the basis of the hypothesis might 

 be contested. When Carlyle was asked to assent 

 to the principle that a body cannot act where it 

 is not, he answered : " With all my heart ; but, 

 pray, where is it .? " And it may be quite well 



