552 PHILOSOPHICAL TRANSACTIONS. [aNNO 1795. 



sary to restore the equilibrium, which has been disturbed by the action of the 

 metals, must pass through the nerve. This experiment I have made, and as I 

 did not find the muscle to contract, I must hold Mr. Volta's opinion on this point 

 to be also ill founded. The fact is, that as far as the contraction of muscles is a 

 test, whether the influence exists or not, and we have no other, it is never ex- 

 cited when 2 metals, or one metal and charcoal are necessary for this purpose, 

 unless these substances touch each other, and are also in contact with some of 

 the fluids formerly mentioned. 



But there is still another requisite for the excitement of the influence, which 

 is a communication, by means of some good conductor of electricity, between 

 the 2 quantities of fluid, to which the dry exciters are applied, beside that which 

 takes place between the same quantities of fluid, when the dry exciters are 

 brought into contact with each other. As from this last circumstance, a complete 

 circle of connection is formed among the different substances employed, it has 

 been imagined by many, that the individual quantity of the influence excited goes 

 the whole round, each time contraction is produced. There is an experiment 

 however, first I believe made by Dr. Fowler, which appears to contradict this 

 opinion. He brought 2 different metals into contact with each other in water, 

 at the distance of about an inch from the divided end of a nerve, placed in the 

 same water, and found that the muscles, which depended on it, were from this 

 procedure thrown into contractions. Now, in this experinient, there was surely 

 room enough for the influence to pass through both metals, and the moisture 

 immediately touching them, without going near to the nerve. I think it there- 

 fore probable, that motions are in no case produced by any thing passing from 

 the dry exciters through the muscles and nerve, but that they are occasioned by 

 some influence naturally contained in those bodies, as moist substances, being 

 suddenly put in motion when the 2 dry exciters are made to touch both them and 

 each other; in like manner as persons, it is said, have been killed by the motion 

 of their proper quantity of the electric fluid. But to return from conjecture to 

 facts, I shall now examine, whether it be always necessary to employ 2 dry ex- 

 citers, that is, 2 metals, or one metal and charcoal, in order to occasion con- 

 tractions. 



Gold and zinc, the first the most perfect of the metals, the other an imperfect 

 one, operate together very powerfully in producing contractions; while gold, and 

 the next most perfect metal, silver, operate very feebly. It would seem there- 

 fore, that the more similar the metals are, which are thus used, the less is the 

 power arising from their combination. Two pieces of the same metal, but with 

 different portions of alloy, are still more feeble than gold and silver; and the power 

 of such pieces becomes less and less, in proportion as they approach each other 

 in point of purity. From these facts it has been inferred, that if any 2 pieces 



