BLECTIIIC EFFECTS Olf FRICTIOK. 13 



1 have made various experiments of the same kind, with Farther proof 

 vjirious bodies, all affording the same general result ; but I "^j^^i^^,^yj*s^^ 

 shall only relate one more, giving another example of a t;ve or neja- 

 body which becomes either po5?7ii;e or w^ga/ioericcording to ''^®* 

 the other body with which it undergoes friction. This is 

 one of the beads, of the size and colour of cherries, worn 

 by indian women, which, as Dr. Lind informs me, consist , 



of an inspissated vegetable oil: they are not soluble by 

 water, and are very elastic. 



Exper. 8. I mounted one of these beads on a spindle, as Exp. 8. 

 in fig. B. The bead, 1, is traversed by a small glass 'd\\s, 

 2, 2, covered with sealing-wax, to the ends of which are 

 adapted pieces of wood, 3 and 4, on the first of which is 

 seen, at 5, the ridge before mentioned, which prevents the 

 spindles from coming out when placed between the pillars of 

 the apparatus. 



1. With a narrow brass rubber, the extremity of which is 

 fitted to the form of the bead, the slowest motion of the 

 winch renders the bead negative, and the brass rubber 

 positive. * 



2. With a sealing-toax rubber like that fig. A, but fitted 

 to the form of the bead, with very little pressure and 

 motion, the bead becomes positive, and the sealing-wax 

 negative. . 



Such are tne constant phenomena observed at the foun- Friction only 

 tain head of all the electric effects, which it is in our power disturbs the 

 to produce; and they depend on friction, respecting which th" Ikctrii." *' 

 various systems have been fabricated. Now from the whole fluid} 

 tenour of these experiments it may be laid down as a funda- 

 mental truth in terrestrial physics, that friction has no 

 other influence in electric phenomena, than that of disturb- 

 ing the cquiUbrivm of the electric fluid, in such a manner, 

 that one body, by acquiring a certain quantity of it above 

 what it had before, is rendered positive, and Uiat the other 

 \s^o\inA negative, as having lost that quantity. It is only j^,,jj ^ i^ ^1^^^ 

 when its equilibrium is disturbed, that the e/ec/ric ^wirf is a'o"^ ni«K>'f'&st 

 manifested to us: the electroscope \s our first test of this ^^ "^" 

 disturbaiice; but if the bodies, eifher coiiV(/wt/or* them- 

 selves, or associated with conduetors, are of a sufficient 

 «i^e, and the electric difference between them has arrived to 



a certain 



