200 



ELECTRICAL EFFECTS PRODUCED BY FRICTIOIf. 



Motive and 

 plan of Mr. 

 De L'jc's ex- 

 periments. 



The appara- 

 tus. 



*' according to its actual, but local (in a certain extent) quanti- 

 '^ ties on them, and in the ambient air. If both the bodies which 

 *• exercise friciion on each other are good conductors, the equi- 

 " Librium being constantly restored, this disturbance is not 

 " perceived : but if one has more disposition than the other to 

 " attract the electric Jiuid thus agitated, with the faculty of 

 " transmitting it to its remote parts ; when the bodies are 

 " sepH rated, either suddenly, or in general before the equili- 

 " hrium of the electric fluid is restored between them, one is 

 '*' io\Midi positive, as having acquired a proportional quantity of 

 *' this fluid, greater than the ambient air, and the other negative, \ 

 " as having lost that quantity." This is the theory of the 

 effects of friction, which, in the same paper, I compare with 

 direct experiments : but before I come to that comparison, I 

 must explam the general plan of those experiments, and its 

 motive. 



8. The obscurity which reigned on the effects oi friction pro- 

 ceeded from a circumstance wanting in most of these experi- 

 ments j they require the insulation, not of one only of the 

 bodies, but of both, either conductor or nonconductor; else 

 the whole of the reciprocal effect cannot be discovered. I had 

 found this necessity by many experiments made with large 

 bodies, with which I could exactly follow the motions of the 

 electric fluid. But I could not suppose it easy for every experi- 

 mental philosopher to procure this apparatus, which I had 

 partly constructed myself j therefore I attempted to prodtice a 

 small apparatus, containing in itself all the parts of the large 

 one, which might easily be obtained by every experimental 

 philosopher ; and having succeeded, I thus introduced, in the 

 same paper, this new plan of experiments on friction. " Mr. 

 " Cavallo has given a table containing the results of his experi- 

 ^' ments of this kind, wherein is found, that certain bodies 

 ** become either negative or positive, according to those by 

 " which they are rubbed. However, there remained to be known 

 " what effect was produced on each of the bodies which exercised 

 *' that friction. This has been one of the objects of my expe- 

 " riments ; for which purpose I kept insulated both bodies, 

 *' exercising/ric/ion on each other, applying electrometers to 

 " both." 

 9. Then follows, in the same paper, the description of the 



appa- 



