ELFXTRIC EFFECTS OF FRICTION. d 



Jatter case, was produced on each of the bodies which exer- 

 cised tln'dt friction. This had been one of my objects in 

 the above mentioned experiments ; for which purpose I 

 kept insulated both bodies exercising/ric/fon on each other, 

 applying to them e/ec/ro.9cope*. It is by experiments thus 

 performed, that I found the general law above expressed ; 

 for when any of the bodies, which may be rendered either 

 positive or negative by friction, was brought to one of these 

 states, the body which had exercised it wasconskntly found 

 in the opposite state: if the former became positive, it had 

 taken some electric fluid from, and \{ negative, it \\^di yielded 

 some fluid to, the body which had txerc'ised friction upon 

 it. Such are the effects, which will be seen in the following 

 experiments. 



The small apparatus, ^which 1 am going to describe, was -^PP^/^jJ"* 

 not at first intended for this purpose; my view in its con- prove the si- 



struction having: been to prove the kind of analogy which niilanty be- 



°, ^' 1 T o • tweentheelec- 



I have established in my former paper, between the electric trie machin* 



machine and the electric column, and even the pile, with re- ^"^ P'^®- 

 spect to its electric property; the only difference in this 

 respect between the electric machine and the latter instru- 

 ments being, that, as in the former the effect is produced 

 hy friction, it requires a mechanical process for its conti- 

 nuance; while in the column and in the pile it is produced 

 by only the association of two proper metals. The surest 

 mode of following the course of the electric fluid, when its 

 equilibrium is disturbed, is by the motions of electroscopes ; 

 but the immediate comparison which I had in view could 

 not be made with any of the usual electric machines ; as the 

 gold-leaf being the only electroscope, that can be effected 

 by a pile or column of a moderate size, it would be torn to 

 pieces by the smallest electric machine hitherto used. This 

 made me think of the construction of so small an electric 

 machine, that the ^o/c?-/f a/* electroscope should not be more 

 affected by it than by my largest column ; but after the first 

 experiments I was induced to construct this small apparatus 

 60 as to be applied to experiments concerning the different • 

 effects o? friction between different bodies. 



The dimensions of this instrument, as represented in the f *•"'* .*PP^™'"* 

 figure Plate I, are, in the parts supposed the nearest to 



