2 1 o Memoir on the Torpedo as imitated by electricity 



the electrical organ is composed, is divided into a 'great number of parti- 

 tions by fine membranes, the thickness of each partition being about the 

 I5oth part of an inch; but the thickness of the membranes which form 

 them is, as he informs me, much less. The bulk of the two organs together 

 in a fish 10^ inches broad, that is, of the same size as the artificial torpedos, 

 seems to be about 24^ cubic inches ; and therefore the sum of the areas of 

 all the partitions is about 3700 square inches. Now 3700 square inches of 

 coated glass T ^ of an inch thick will receive as much electricity as 30,500 

 square inches ,055 of an inch thick * ; that is, 305 times as much as the plate 

 of crown glass mentioned in Art. 411, or about 2f times as much as my 

 battery, supposing both to be electrified by the same conductor; and if the 

 glass is five times as thin, which perhaps is not thinner than the mem- 

 branes which form the partitions, it will contain five times as much 

 electricity, or near fourteen times as [much as] my battery. 



437] It was found, both by Dr Williamson f and by a committee 

 appointed by the Philosophical Society of Pennsylvania, that the shock 

 of the Gymnoius would sometimes pass through a chain, though they never 

 perceived any light. I therefore took the same chain which I used in the 

 foregoing experiments, consisting of 25 links, and suspended it by its 

 extremities from the extreme hooks of the machine described in Art. 433, 

 and applying the end of the machine to the negative side of the battery, 

 touched the positive side with a piece of metal held in the other hand, so 

 as to receive the shock through the chain without its passing through the 

 torpedo; the battery being charged to such a degree that the shock was 

 considerably stronger than what I usually felt in the foregoing experi- 

 ments. I found that if the chain was not stretched by an additional 

 weight, the shock did not pass at all: If it was stretched by hanging a 

 weight of seven pennyweights to the middle link, it passed, and a light 

 was visible between some of the links ; but if fourteen pennyweights were 

 hung on, the shock passed without my being able to perceive the least 

 light, though the room was quite dark; the experiment being tried at 

 night, and the candle removed before the battery was discharged J. It 

 appears, therefore, that if in the experiments made by these gentlemen 

 the shock never passed, except when the chain was somewhat tense, which 

 in all probability was the case, the circumstance of their not having per- 

 ceived any light is by no means repugnant to the supposition that the 

 shock is produced by electricity . 



* Vide note in p. 200. 



f " Experiments and Observations on the Gymnotus Electricus, or Electrical 

 Eel." By Hugh Williamson, M.D. Communicated by John Walsh, Esq., F.R.S. 

 Phil. Trans. LXV (1775), p. 94. 



f [Art. 613.] [See Note 29, p. 419 and Introduction.] 



