472 PHILOSOPHICAL TRAiNSAC 1 IONS. [aNNO 1778. 



tion, and retained a long while the electric power, though not so long as the 

 resinous cake. 



I will now explain the nature of an elect rophore in a manner more familiar to 

 electricians, who understanfl the received theory, by taking, instead of an elec- 

 trophore, only a common pane of glass, adapted as a magic picture, with this 

 difference only, that both coatings may be taken oft' by silk strings fastened to 

 them, or by pieces of sealing wax. Having established a free communication 

 between the common stock and the under coating, apply the upper coating to 

 the prime conductor of an ordinary electrical machine, the pane of glass is 

 charged in the common way. The prime conductor has forced a superabundant 

 quantity of electric fluid on the surface next to it, by means of the coating, and 

 as much is forced out of the opposite surface, and driven into the common 

 stock. Open a metallic communication between the two coatings, and instantly 

 the glass will be what is called discharged : and indeed it is so to all appearance ; 

 but if we examine more accurately what has hap[)ened, we shall find that the 

 upper metallic coating has parted, by the discharge, with all the electric fluid 

 which the priirie conductor had forced on it, and even with that part of its own 

 electric fluid which the rej^ellent power of the superabundant electric fluid, com- 

 municated to that surface of the glass by the force of charging, had driven into 

 it; and that the under coating has recovered as much as the glass had forced 

 through it into the common stock, and has, above that, acquired or absorbed 

 that additional quantity which that surface of the glass, being brought into a 

 negative state, had drawn from the metal itself. And thus it will appear tliat 

 the glass had, in the discharging, by no means parted with that state of elec- 

 tricity which it had acquired by the force of charging. 



Now glass, and all electric substances, receiving with more difficulty a state 

 of electricity, and parting with it with more reluctance, the consequence must 

 be, that when the two coatings are separated from the glass, so as not to be in 

 the way of absorbing or losing the electric fluid by other conducting bodies being 

 near them, the upper coating, which was positive when the glass was charged, 

 and nearly in its natural state, when after the discharge it lemained in conjunc- 

 tion with the glass, must now give signs of a negative electricity, iiaving lost by 

 the discharge a share of even its natural electric fluid in the manner mentioned. 

 The under coating, which was in a negative state when the glass was charged, 

 and (like the other coating) in a natural state when after the discharge it re- 

 mained in conjunction with the glass, must now, being separated from the 

 glass, be in a positive state^ because it had absorbed a quantity of electric fluid 

 in the manner explained; which superabundant quantity it must take with it in 

 the moment of separation from the glass, because the glass, being unwilling 



