188 EXPERIMENTS ON ELECTRICITY. 



each other, but fo that B was not connected with the earth. 

 He then touched the plate A with the blade of a knife, and 

 the plate B at the fame time with the point of a foftened iron 

 wire. With fixteen revolutions the gold leaf diverged about 

 one third of an inch positively. The doubler was then again 

 deprived of electricity, and the revolving plate B placed as in 

 the laft experiment. The knife was applied to B inftead of A, 

 and the foft iron wire to A inftead of B, which opened the 

 gold leaf negatively at fifteen revolutions. Thefe experiments 

 were repeated very often, and the electricity changed each 

 time ; being always pofitive in the plate touched with the 

 knife. He remarks, that it would appear incredible, that fo 

 minute a difference of adhefive electricity as that which might 

 be fuppofed between two metals fo nearly alike as hardened 

 fteel and foft iron could be distinguished, had not the frequent 

 repetition of experiments confirmed it. 



with other fub- He proceeded to make fimilar experiments, which are ta^ 

 bulated, of different fubftances, namely, lead ore and lead ; 

 lead and iron wire ; lead ore and iron wire ; tin foil and iron 

 wire; zinc and iron wire. All the experiments having been 

 made by double contact and alternate application of the oppo- 

 site fubftances to the plates A and B, he alfo by tingle contact 

 determined whether the adhefive electricity, or to ftate the 

 fact more unexceptionably, the electricity produced by each 

 fubftance in the doubler, was pofitive or negative. I have 

 thought it lefs immediately neceflary to ftate the particulars of 



•ObjefHon from thefe experiments, becaufe I prefume that the fubftances were 



the effeft of y^ • ^ hand d from a var ; ety f f a ft s I think we are 



fn&ion by the ' J 



hand. justified in concluding that friction, or a contact equivalent to 



friction, between the human Skin and the fubftance thus held, 



will produce electricity more than fufficient to render it unne- 



ceflary to look for any other caufe, or at leaft quite fufficient to 



render our investigations uncertain when fo conducted. That 



is to fay, I think the remits will rather confift of determinations 



of the kind of electricity produced by friction of the hand upon 



the feveral fubftances, than any new or peculiar affection of 



the fubftances themfelves. 



Theory of flee- Among other interefting obfervations, for which I muft 



eric excitation. re f er j} ie reader to the work itfelf, he gives a Simple theory of 



. * the excitation of glafs, and other electrics ufed in the con-. 



ftruction of our machines. He remarks, that when the ft Ik 



3 flap 



