DUFAY'S EXPERIMENTS. 479 



on the subject. In the spring of 1733 he learned, with 

 absorbing interest, of the achievements of Gray and 

 Wheler, and determined at once to prosecute them further 

 and in entirely new directions. 



At the very outset he makes a discovery which over- 

 throws the distinction between electrics and non-electrics, 

 and brings to an end the efforts to enlarge the list of the 

 former, which had continued ever since the time of Gil- 

 bert. The number of different substances which he tests 

 is legion all sorts of woods and stones, especially all 

 those materials which earlier investigators had been un- 

 able to electrify. Some he finds require more u chafing or 

 heating" than others; some, such as the gums, he cannot 

 so treat without rendering them viscid; while the electrifi- 

 cation of the metals is so slight that he doubts whether he 

 has really recognized it: but in the end he announces that 

 all bodies (the metals and soft substances excepted) are 

 endowed with the property which for ages was supposed 

 to be peculiar to the amber, or, in other words, become 

 electrics by themselves (electriques par eux-me"mes). 



Then he turns to Gray's experiments on conduction and 

 verifies them, but in so doing his attention becomes con- 

 centrated upon the supports for the electrified body Gray's 

 silk strings and cakes of resin. He varies the material 

 of which these supports are made. Pieces of metal, or 

 wood, or stone, on wooden or metal standards, he could 

 not electrify by bringing the excited glass tube near to 

 them, but when he substituted glass supports then he 

 could do so. Immediately it dawns upon him that the 

 possibility of electrifying a body does not depend upon the 

 nature of the body itself so much as upon its being insu- 

 lated, so that the virtue cannot escape from it. Again he 

 collects a great variety of objects woods and stones and 

 amber and agate, even oranges and books and red-hot 

 coals and placing them, one after another, on the glass 

 standards, brings the rubbed glass tube near to them, 

 when every one of them becomes electrified; and what 



