28 PHILOSOPHICAL TRANSACTIONS. [aNNO I77t\ 



connected to the same prime conductor, as a plate of crown glass, the area of 

 whose coating is 100 square inches, and whose thickness is -rH-g- of an inch ; 

 that is, such that one square foot of it shall weigh lOoz. 12dwts. ; and conse- 

 quently, the whole hattery contains about 1 10 times as much electricity as this 

 plate.* 



I found, on trial, that though a shock might be procured from this artificial 

 torpedo, while held under water, yet there was too great a disproportion between 

 its strength, when received this way, and in air ; for if I placed one hand on the 

 upper, and the other on the lower surface of the electric organs, and gave such 

 a charge to the battery, that the shock, when received in air, was as strong as, 

 I believe, that of the real torpedo commonly is; it was but just perceptible when 

 received under water. By increasing the charge indeed it became considerable : 

 but then this charge would have given a much greater shock out of water than 

 the torpedo commonly does. The water used in this experiment was of about 

 the same degree of saltness as that of the sea ; that being the natural element of 

 the torpedo, and what Mr. Walsh made his experiments with. It was composed 

 of one part of common salt dissolved in 30 of water, which is the proportion of 

 salt usually said to be contained in sea water. It appeared also, on examination, 

 to conduct electricity not sensibly better or worse than some sea water procured 

 from a mineral water warehouse. It is remarkable, that if I used fresh water in- 

 stead of salt, the shock seemed very little weaker, when received under water 

 than out ; which not only confirms what was before said, that salt water con- 

 ducts much better than fresh ; but I think shows, that the human body is also 

 a much better conductor than fresh water : for otherwise the shock must have 

 been much weaker when received under fresh water than in air. 



As there appeared to be too great a disproportion between the strength of the 

 shock in water and in air, I made another torpedo, exactly like the former, ex- 

 cept that the body part instead of wood was made of several pieces of thick lea- 

 ther, such as is used for the soles of shoes, fastened one over tiie other, and cut 

 into the proper shape ; the pieces of pewter being fixed on the surface of this, as 

 they were on the wood, and the whole covered with sheep skin like the other. 

 As the leather, when thoroughly soaked with salt water, would suffer the elec- 

 tricity to pass through it very freely, I was in hopes that I should find less dif- 

 ference between the strength of the shock in water and out of it, with this than 

 with the other. The event answered expectation ; for it required about 3 times 

 as great a charge of the battery, to give the same shock in air, with this new 



* I find, by experiment, that the quantity of electricity which coated glass of different shape* 

 and sizes will receive witli the same degree of electrification, is directly as the area of the coating, 

 and inversely as tlie thickness of the glass ; whence the proportion which tlie (jnantity of electricity 

 m this battery bears to that in a glass or jar of any other size, may easily be computed.— Orio-. 



