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apparatus with which these experiments were raade : its figure, 

 which is at the head of the paper, is half the size of the appa- 

 ratus itself; and it may be seen, in that figure, that it is, in 

 fact, a very small electric machine, wiih a revolving part and a 

 rubber : but it is so constructed, that both these parts rany be 

 easily changed, for producing friction between different bodies, 

 the effects of which are always shown by the gold leaf electro- 

 meters. I do not tf-ink it necessary to compare directly every 

 part of these experiments with Dr. Maycock's theory ; he is 

 so intelligent, that, had he read my paper, he would have 

 found himself those relating to the objects on which we dis- 

 sent ; therefore, I shall only indicate briefly some of these 

 points. 



10. The fourth proposition of Dr. Maycock's theory, above '^^- Maycock'g 

 quoted, is the following : " ThQ friction of two bodies, similar ^^^^Q^ refused" 

 " in every respect to one another, produces no excitement." by experi- 

 This is the immediate consequence of his theory, but is con- '"^'^ " 



trary to mine : here, therefore, is afforded a criterion between 

 them ; and he might have found the decision in my paper. 

 There, after having explained my theory, — that, in ihefriction 

 between two bodies, which operation agitates the electric fluid 

 on their surface, the body which is the most disposed to seize 

 upon that fluid, and to transmit it to its remote parts, becomes 

 positive, and the other negative, — I added : '^ 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. This effect cannot be ob- 

 " served with perfect conductors, as on them the equilibrium of 

 " the electric fluid is instantly restored ; but there is a known 

 '' experiment with tw« pieces ©f the same suh riband, in 

 " which, by making one piece pass rapidly in length on one 

 " part only of the other, the former becomes positive, by car- 

 *' rying off some electric fluid from the latter, which thus is 

 *' rendered negative, by losing that fluid." 



11. These experiments I have repeated many times; by Erperiment 

 using pieces of wide and strong silk riband ahoni a yard long, with silk n- 

 at the extremities of which were fixed proper pieces of wood, 



to keep them stretched ; one being held very steady, while 

 somebody made the other pass rapidly on one part of the for- 

 mer : then applying each of them instantly to the top of a 



gold 



