aoo Memoir on the Torpedo as imitated by electricity 



to discharge it in the above mentioned manner by means of the wire Ww. 

 In experiments with this torpedo under water, I made use of a wooden 

 trough ; and as the strength of the shock may, perhaps, depend in some 

 measure on the size of the trough, and on the manner in which the torpedo 

 lies in it, I have, in Fig. 4, given a vertical section of it ; the torpedo being 

 placed in the same situation as in the figure. ABCDE is the trough; the 

 length BC is 19 inches; the depth A B is 14; and the breadth is 13; conse- 

 quently, as the torpedo is two inches thick in the thickest part, there is 

 about 5^ inches distance between its sides and those of the trough. 



411] The battery was composed of 49 jars, of extremely thin glass, 

 disposed in 7 rows, and so contrived that I could use any number of rows 

 I chose. The outsides of the jars were coated with tinfoil; but as it would 

 have been very difficult to have coated the insides in that manner, they 

 were filled with salt water. In a battery to answer the purpose for which 

 this was intended, it is evidently necessary that the metals serving to 

 make the communications between the different jars should be joined 

 quite close : accordingly care was taken that the contacts should be made 

 as perfect as possible. I find, by trial, that each row of the battery contains 

 about 15! times as much electricity, when both are 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 T ^,j of an inch ; that is, such that 

 one square foot of it shall weigh 10 oz. 12 dwts. ; and consequently, the 

 whole battery contains about no times as much electricity as this plate*. 



412] The way by which this was determined, and which, I think, is 

 one of the easiest methods of comparing the quantity of electricity which 

 different batteries will receive with the same degree of electrification, was 

 this: First of all, supposing a jar or battery to be electrified till the balls 

 of the above-mentioned electrometer separated to a given distance, I 

 found how much they would separate when the quantity of electricity in 

 that jar or battery was reduced to one-half. To do this, I took two jars, 

 as nearly equal as possible, and electrified one of them till the balls sepa- 

 rated to a given degree, and then communicated its electricity to the other; 

 and observed to what distance the balls separated after this communi- 

 cation. It is plain, that if the jars were exactly equal, this would be the 

 distance sought for; as in that case the quantity of electricity in the first 

 jar would be just half as much after the communication as before; but as 

 I could not be sure that they were exactly equal, I repeated the experi- 



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

 different shapes and sizes will receive with the same degree of electrification, is 

 directly as the area of the coating, and inversely as the thickness of the glass; 

 whence the proportion which the quantity of electricity in this battery bears to that 

 in a glass or jar of any other size, may easily be computed. [See Art. 584. The 

 charge of the first row of jars was 64,538, and that of the whole battery about 

 481,000 inches of electricity.] 



