HYPOTHESIS OF TWO FLUIDS. 419 



warmed and rubbed with silk or woollen cloth, 

 they repelled light bodies in their vicinity; but 

 that when resinous bodies were made electric by 

 friction in the same manner, they attracted light 

 bodies which had been electrified by excited 

 glass. Having caused a piece of gold leaf to be 

 repelled, and suspended in the air by an elec- 

 trified glass tube, and meaning to chase it about 

 the room by a stick of excited gum copal, he 

 found that, instead of being repelled by it as it 

 was by the glass tube, it was eagerly attracted. 

 From which he concluded that there were two 

 kinds of electricity, residing in two different 

 classes of bodies ; one of which he termed vitreous, 

 and the other resinous, and that bodies charged 

 with either kind repel bodies charged with the 

 same kind, but attract bodies charged with the 

 other kind. But when it was afterwards dis- 

 covered by Dufay, that all bodies acquired the 

 power of attracting and repelling the same sub- 

 stances, according to the manner in which they 

 were electrified, he frankly acknowledged that 

 vitreous and resinous electricity were only dif- 

 ferent degrees of one and the same fluid. 

 (Priestley's Hist, of Electricity, pp. 43 and 412.) 

 Yet the doctrine of two electricities has been 

 constantly imputed to Dufay by nearly all writers 

 on the subject for the last 70 years. 



It is said by those who still maintain the doc- 

 trine of two fluids, that if the gold leaves of an 



