VITREOUS AND RESINOUS ELECTRICITIES. 485 



contracted will be drawn by the latter. And this leads me 

 to conclude that there are perhaps two kinds of different 

 electricities" 



Further tests confirm the belief, and he announces that 

 electrified glass repels electrified glass, or all bodies re- 

 ceiving electricity therefrom, and attracts electrified amber 

 and all bodies to which its charge has been communicated. 

 In other words, he had established the fundamental law 

 that similarly-electrified bodies repel, while dissimilarly- 

 electrified bodies attract one another. 



He calls the electricity yielded by glass vitreous, and 

 that -derived from the rubbed gum resinous / because 

 4 'glass and copal are the two substances which have led 

 me to the discovery of the two different electricities." 



Thus Dufay had found that all bodies may become elec-* 

 trie either by direct communication or by induction; that 

 the so-called electrics are the least suitable to convey the 

 virtue; that the electric light may appear as fire or burning 

 sparks, and that there are two different kinds of electricity, 

 of which one attracts bodies repelled by the other; and 

 that bodies, if similarly charged, repel, while attracting if 

 dissimilarly electrified. These are only his more important 

 conclusions; others, although ingenious and original, re- 

 late to details which need not be entered into here. 



In December, 1733, Dufay wrote a brief synopsis 1 of the 

 long memoirs which he had already published in the 

 annals of the French Academy, and sent it to the Duke 

 of Richmond and Lenox for presentation to the Royal 

 Society and (with characteristic diplomacy) to Mr. Gray, 

 "who works on this subject with so much application and 

 success, and to whom I acknowledge myself indebted for 

 the discoveries I have made, as well as for those I may 

 possibly make hereafter, since it is from his writings that 

 I took the resolution of applying myself to this kind of ex- 

 periments. " Whether in all the history of discovery there 

 exists a more handsome recognition than this of the work 



'Phil. Trans., No. 431, p. 258, 1733. 



