Vdtii on Auhnal Hile^ric'ify. 6l 



nt) fireani can be formed from right to left, or contrariwife, 

 capable of exciting convulfive movements. 



There are other cafes, however, and other modes of com- 

 bination, where the powers are equally in equilibrium, and 

 where no current of the eleftric fluid can take place ; or, at 

 leaH:, none of fuch a force as to make an impreflion on the 

 tendereft nerves, or to excite any convulfive movement in the 

 bell prepared frog that may be placed in the circle, notwith- 

 ftandin^ the intervention of two or more dilTerent kinds of 

 metals. This is the cafe when each of thefe metals is placed 

 between two moill conductors, or ofthefecond clafs, and 

 which ar& very nearly of the fame kind, as fig. 7 ; or when, 

 in a circle of three pieces, two of them of the fame mela!, 

 and one of a different metal, are fo conncfted, that the latter 

 is immediately between the other two, as fig. 8. 



When one of the ends of the middle piece of metal A is 

 immediately applied to one of the two pieces Z, but, inftcad 

 ^f immediately touching with the other end, the other piece Z 

 touches an intermediate ccndut5tor of the feconu clafs, cither 

 great or fmall, either a drop of water, a piece of raw or boil- 

 ed fled), or of fponge not nioift, pallc of meal, jelly, foap, 

 cheefe, or the white of an egg boiled to hardneis, in this 

 new combination, reprefented by fig. 9, (where a conduftof 

 of the fecond clafs m is between two of the firll clafs, A and Z) 

 the powers are no longer oppofed to each other ; and this is 

 fufficient to determine an electric ftream. When ^, there- 

 fore, in fig., 9, is a prepared frog, it will always be violently 

 agitated as often as this circle vi made complete. 



It may be readily perceived that the tv.-o laft experiments, 

 reprdeiitcd bv fig. 8 and 9, coincide with thofe announced 

 by M. Humboldt, where a drop of v/atcr, a fmall bit of frofh 

 meat, or a very thin Itratum of any fluid, performs the whole 

 wonder. When another drop of water, or any other aqueous 

 sondudlor, is applied bctwcn the other end ot A and tho 

 Either cyrrcl'ponding piece Z (hs (licv.n fig. 10), each piece 

 «f metal is infajated, as I (hall exprefs it, between two 



ac^iieuut 



