ELECTRIC EFFECTS OF FRICTION, 9 



in order to yield to the inequalities of the cylinders or plates 

 while it presses upon them ; but the materials of the cu- 

 shions are liOt sufficiently conducting to permit the loss, 

 which its ruhbed part underj^oes, of the fluid carried off by 

 the giass^ to be soon repaired l;y the ground; whereas this 

 is effected by the metallic amalgam, from which the glass 

 takes readily some electric fluid, as, in the above experi^ 

 ment, it takes it from the brass rubber. Metallic plates 

 would produce the same effect on the cylinders and plates oi' 

 electric machines, if the former were sufficiently pliable. 



The general effect of friction between two bodies, as 1 General eff«ct 

 have said above, is, that if one becomes positive or negative, *^ 

 the other is found in a contrary state. This holds not only 

 between bodies of different natures, but; even between the 

 same kinds of bodies, if one be made to pass in length over 

 one part only of the other. 1 his effect cannot be observed 

 with perfect conductors, as on them the equilibrium of the 

 electric fluid is instantly restored ; but there is a known ex- erempHfied 

 periment made with two pieces of the same silk riband, in pieces ^fri« 

 which, by making one piece to pass rapidly in length on one band, and 

 part only of the other, the former h^come^ positive, by car- 

 rying oft' ^ome electric fluid from the latter, which thus is 

 rendered negative, by losing that fluid. I have tried the 

 same experiment with glass, in the following manner. 



Exp. 3, At the end of a brass spring I tixed a flat piece Exp. 5, with ^ 

 of the same g^/a5« as the small cylinder, and used it as a^^ * 

 rubber, in the same manner fiss in the former experiments. 

 Both pieces of glass being therefore insulated, there was no 

 sensible effect on either of the electroscopes; as the im- 

 mediate effect and consequence of friction between these 

 small bodies, being confined within the bodies themselves, 

 were too small to be perceived. I then held my finger on 

 the brass spring near the flat piece of glass, in order to re- 

 store to the latter, from the ground, the fluid carried off by 

 the glass cylinder ; and having turned rapidly the winch for 

 a little time, the electroscope 11 diverged positively. This 

 is the same effect as produced on the riband passing rapidly 

 over a part only of another similar: the glass, which turned, 

 carried off some electric fluid from the other glass, which 

 w^s rubbed only on one point; arid as the latter now re- 

 paired 



