104 Ohervallons on Mr. Donovan's Reflections ^ &c. 



stance. While, if both bodies which exercise friclion on each 

 other are good conductors, the equihbrium is iccessantly restored ; 

 but if one has more disposition than the other to attract the 

 electric fluid thus agitated, with the faculty of transmitting it to 

 its remote parts, when the bodies are separated before the eqid- 

 lihrium. is restored between them, one is fomid positive and the 

 other 7iegative. 



2S. These effects are distinctly demonstrated by a small elec- 

 tric madiine, the figure of which is at the head of my paper in 

 Mr. Nicholson's Philosophical Journal for January 181 1, under 

 the title of " Experiments concerning the Electric Machine, 

 showing the Effects of Friction between Bodies." 



29. M. Cavallo has given a table containing the results of his 

 experiments of this kind, wherein we find that certain bodies 

 become either positive or negative hy friction, according to those 

 by which they are rubbed; but the manner in which his experi- 

 ments were made did not indicate the effect produced on the 

 rubber itself, because it was not insulated. I thought it there- 

 fore very important to the doctrine of electricity, to have both 

 effects indicated by electrometers. This I obtained by the ap- 

 paratus described in that paper ; in which the bodies rubbed are 

 spindles turned by a winch, and various rubbers made to press 

 on the spindles by proper springs. A small insulated prime 

 conductor is connected by one of its extremities to the spindles, 

 and by the other with a gold-leaf electrometer. The rubbers are 

 insulated, and each of them when applied is made to commu- 

 nicate with a similar gold-leaf electrometer. 



30. The constant result of these experiments was, that the 

 quantity of p/ws on one side was equal to the quantity of minus 

 on the other. Now the friction being reciprocal, the supposi- 

 tion of the opening of the pores cannot explain that phzenomenon, 

 since they ought to be opened equally in the rubbing as in the 

 rubbed bodies. 



31. The effect of friction, as I have said above, is to set in 

 motion on the surface of the bodies, and that, if the body which 

 recedes from the point of friction finds in its way a pointed con- 

 ductor, it transmits to the latter a part of that fluid, which is 

 the effect of the common electric machine : but the same phae- 

 nomenon extends further ; for that effect takes place between 

 bodies of the same kind, if they be non-conductors. This is 

 proved by Exper. 3, p. 9, of the same number of the Philosophical 

 Journal. 



32. A flat piece of the same glass as the spindle, being held 

 at the end of a brass spring, and used as a rubber on the spindle, 

 holding the brass piat in my hand near the glassj in order to 



restore 



