mm XhntaSl of eond-uSHilg "Subjlances. ^(fj 



In regard to the fenfe of fight, which I alfo found might 

 •be affedled by the weak current of the electric fluid, arifing 

 from the mutual contaA of two different metals in general, 

 and in particular, of a piece of fi'.vcr and one of zine, it was 

 natural to expeft that the fvinfation of light, excited by my 

 new apparatus, would be Itronger in proportion ae it con- 

 tained a greater number of pieces of thefe metals; each pair 

 •of which, arranged in the proper manner, adds a •degree of 

 force to the faid cleilric -current, as all the other experiments 

 iliow, and particularfy ihaCe with the elettromcter afiifted 

 by the condenfer, whieli I have only tnentioned., and which 

 I (hail defcribe on another occafion. But 1 was furprifcdl 

 to find that, with lo, 20, 30 pairs, aud more, the flafli pro- 

 duced neither appeaued longer and more extended, nor much 

 brighter than with ane .pair. It is true, however, that this 

 fenfation of weak and tranficnt light, is excited by fuch aa 

 •apparatus much «afier and in different wavs. To fucceed. 

 Indeed, with one pair, the follouing are alnwft the only 

 methods ; rjiz, that one of the metallic piieces fliould be ap- 

 plied to the ball of the eye, or the eye -lid well moifteued, 

 and that it (lioudd be made to touch the other metal applied 

 to the other eye, or hdd an the mouth, which produces a 

 a flafli much more beautiful ; or, that thi« fecond metallic 

 piece fliouM be held in themoii^cned haiud and •then brought 

 into contaft with the former; or, in the latt place, that liiefe 

 two plates fliould be appiicd to certain parts of the iniide of 

 the mouth, making them cnnmaunicate with each other. But 

 with an apparatus of 20 or 30 pairs, &c. the fame flalh wili 

 be produced by applying the end of a metallic plate or rod, 

 placed in communication with one of the extremities of the 

 apparatus, to the eye., while with one baud \ ou form a proper 

 communication with the other extremity; by briuinne, I 

 fay, this plate into contact not only with the eye or any part 

 of the mouth, but even the forehead, the nofe, the cheeks, 

 Jips, chin, and even the throat; in a word, every part and 

 point of tlie viiage, which mud only be well moiltened before 

 they are appiicd to tin; metallic plate. The form as well as 

 the force of this tranfiem light which is perceived varies a 

 Uuie, if the places of the face to which the attion of the 

 ii r 3i cleclrift 



