34 PHILOSOPHICAL TRANSACTIONS. [aNNO 1770. 



has shown, that each of the prismatical cokimns of which the electrical organ 

 is composed, is divided into a great number of partitions by fine membranes, the 

 thickness of each partition being about the 150th part of an inch; but the 

 thickness of the membranes which form them is, he says, much less. The bulk 

 of the 2 organs together, in a fish 10^- inches broad, that is of the same size as 

 the artificial torpedos, seems to be about 24-1- 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, -Hr-g- of an inch thick, will receive as much elec- 

 tricity as 30500 square inches .055 of an inch thick ; that is, 305 times as much 

 as the plate of crown glass beforementioned, or about 2^- times as much as my 

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

 glass is 5 times as thin, which perhaps is not thinner than the membranes which 

 forms the partitions, it will contain 5 times as much electricity, or near 14 times 

 as my battery. - 



It was found, both by Dr. Williamson and by a committee appointed by the 

 Philosophical Society of Pennsylvania, that the shock of the Gymnotus 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, con- 

 sisting of 25 links, and suspended it by its extremities from the extreme hooks 

 of a machine, 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 consi- 

 derably stronger than what I usually felt in the foregoing experiments. I found 

 that if the chain was not stretched by any additional weight, the shock did not 

 pass at all : if it was stretched by hanging a weight of 7 pennyweights to the 

 middle link, it passed, and a light was visible between some of the links; but if 

 14 pennyweights were hung on, the shock passed without my being able to per- 

 ceive the least light, though the room was quite dark ; the experiment being 

 tried at night, and the candle removed before the battery was discharged. It ap- 

 pears therefore, that if in the experiments made by these gentlemen, the shock 

 never passed, except when the chain was somewhat tense, which in all proba- 

 bility was the case, the circumstance of their not having perceived any light, is 

 by no means repugnant to the supposition that the shock is produced by 

 electricity. 



XHI. Observations on Respiration, and the Use of the Blood. By Joseph 

 Priestley, LL. D., F. R. S. p. 226. 



Reprinted in this author's works on Air. 



