308 ToJ/cript to Volta^s Letterg 



brafs, while In contail with it. This was confirmed by th« 

 following experiment, whic h is a real experimentum cruets. 



II. I revcrfed the experiment, fo that the filver was in 

 contact with one of the fixed plates, and the tin with the 

 moveable one. The eleftricity which I obtained from the 

 latter, after the apparatus had remained a fufficicnt time in 

 that pofition, was negative (— E); while that of the fixed 

 plate was pofitive ( + E) . 



III. I applied only the tin wire to the moveable plate, and 

 infulatcd the two fixed ones, or brought them into eom- 

 munieation with the table or any other moid conduftors 

 with which the tin wire was in contact. This fimple eonta<5t 

 of the tin with the brafi, of which the moveable plate con- 

 fills, is fufficient to excite in it a very fmall degree of nega- 

 tive eleftricity ; only a longer time is required. 



Thofe acquainted with the a£lion of elcftric atmofpheres, 

 and the conftru6bion of the doubler, w-ill need no farther 

 explanation to enable them to comprehend the mode of ac- 

 tion of this very ingenious inftrumcnt; how the eleftricity, 

 once obtained from the moveable plate, muft occafion an' 

 oppofite kind in the fixed plates, and vice verfa ; how the 

 oppofitc kinds of ele£lricity are increafcd by each revolution 

 of the machine. See. In the prefent experiment, therefore, 

 when the moveable plate is — E, the fixed plate muft be +E. 

 IIL This is the reverfe of the former. The piece of tin 

 was applied to one of tlie fixed plates, and tlie moveable one 

 was inlulated from all metallic contaft. The refult was now 

 reverfed ; that is, the fixed plates were eleftrificd negatively, 

 and the moveable one had pofitive eleftricity. 



All thefe experiments fucceedmuch better, and in a fhorter 

 time, if, during the mutual conla^l of the different metals, 

 the moveable plate be oppofite to either of the other two that 

 are fixed ; but ftill better when a piece of thick paper, fucli 

 us a card, not moilt, and of a thicknefs eqyal to the inter- 

 mediate fpace, is placed between the two plates that ftand* 

 «ppofitc to each other. It is of advantage to leave the card 



forae 



