476 



ELECTRICITY. 



Ftctctiptin 

 P.lmriritr. 



PLATE 



Experi- 

 mcnttof M. 

 Gtcftoy. 



Carendiih's 

 explanation 

 of the dec- 

 tricityoftht 

 torpedo. 



management of the electric fluid ; especially a it ap- 

 pears evident, from Mr Walsh's experiment*, that the 

 will of the animal does absolutely controul the electric 

 powers of its body, which must depend on the energy 

 of the nervm," 



In Fig. 1. we have given a representation of the un- 

 der surface of a female torpedo. Below a is seen the 

 right electric organ displayed by flaying off the skin b, 

 e are the nostrils in the form of a crescent, d the mouth 

 in a crescent contrary to that of the nostrils, and fur- 

 nished with several rows of small hooked teeth, e the 

 bronchial apertures, five being on each side, /"the place 

 of the heart, ggg the place of the anterior transv .TM- 

 cartilages, hfi the exterior margin of the great lateral fin, 

 i i it* inner margin confining with the electric organ, If 

 the articulation of the great lateral fin with the scapula, 

 / the abdomen, m mm the place of the posterior trims- 

 verse cartilage, which is single, united with the spine, 

 and supports the smaller lateral fins on each tide, nnnn 

 the two smaller lateral fins, o the anus, and p the fin 

 of the tail. 



M. Gcoffroy has more recently examined the anatomy 

 of the other electric fishes, and has not obtained, in the 

 case of the torpedo, results differing greatly from those 

 of Dr Hunter. He has analysed the fluid which is 

 contained in the cells of the hexagonal tubes, and lias 

 found that it is composed of albumen and gelatine ; he 

 also found organs analogous to those of the torpedo 

 in other species of the raia, which do not exhibit any 

 electrical properties. This transparent gelatinous fluid 

 was considered by^^r Ingenhouz as the reservoir of the 

 electrical power. 



As the experiments of Mr Walsh were not con- 

 sidered as affording a sufficient proof of the identity of 

 the shock of the torpedo with that produced by a Ley- 

 den phial, Mr Cavendish made an attempt to imitate the 

 effects of the torpedo by electricity. The principal 

 difficulty that required explanation was the production 

 of a shock when the fish was held tinder water, and, in 

 other circumstances, where the electricity had a much 

 readier passage than through the person's body. Mr 

 Cavendish explains this by stating, that when a com- 

 munication is made between the positive and negative 

 side of a jar by any number of different circuits, some 

 electricity will pass along each, and a greater quantity 

 through those in which it meets with the least resist- 

 ance. In like manner, when any person lays one hand 

 on one surface of the electric organ of the torpedo, and 

 his other hand on the other surface of the organ, a part 

 of the fluid will pass through his body ; but if one of his 

 hands is laid on the tail instead of the other surface of 

 the organ, part of the fluid will still pass through him, 

 though less in this case than before. Owing to the moist- 

 ness of the body of the torpedo, some electricity will 

 pass through him, even if his hands are laid upon any 

 two parts of the animal, provided one of these parts is 

 nearer to the upper surface of the organs than the other. 

 Upon the same principle, if the torpedo is plunged in 

 water, the electricity will pass through the water in all 

 directions, and even to great distances from the body 

 of the animal ; and the nearer any part of the water is to 

 the fish's body, the greater quantity of fluid will be 

 transmitted. Hence if any person touches the fish in 

 this situation, either with one of his hands on the supe- 

 rior surface of its electric organ, and the other on the 

 inferior one, or in any of the other ways formerly men- 

 tioned, a certain quantity of the electricity will pass 

 through his body, but certainly less than when the 

 is received*^ in the air ; and the same thing will 



happen, even if he does not touch the fish at all, but naeriptir* 

 plunges his hands in the water, so that one hand is nearer Eleeiruiiy. 

 the upper surface of the electrified organs than die other. ,*"" "XT?' 



rrL i i-,,- i i i ( JVVi-nduh s 



Ine second difficulty which requires explanation, fv p<. r j, 

 is, that no spark, or sound, or electrical attraction is per- <m the i-Kv. 

 ceiMil. In order to cxpl.iin this Mr Cavendish made "' 

 experiments with anumber of jars, for tliepiirpose of find- ' lorpedn. 

 ing through what distance the electric spark will fly 

 when a shock of a given magnitude u contained in one 

 or more Jan. The result of these experiments was, 

 " that the distance to which the spark will fly is in- 

 versely in a rather greater proportion than the" square 

 root of the number of jars." That is, a i-lmrge of a 

 certain magnitude contained in 4 jars passes through a 

 space of T V of an inch. The same charge when contain- 

 ed in 1 00 jars will scarcely pass through r \ of an inch. 

 1 fence the torpedo may contain as much electricity as 

 will give a shock, without being able to make it paas 

 through such a space f air as is necessary to produce 

 the electric spark. Mr Cavendish explains the absence 

 of attraction and repulsion by the analogous fact, that, 

 in a large battery, so weakly electrified, that its shock 

 will not pass through a chain, which is the case with 

 the torpedo, a pair of pith balls suspended from the 

 discharging rod will not exhibit any divergence. 



In order to establish these conclusions more complete- Cavendish'* 

 ly, Mr Cavendish endeavoured to make an artificial artificial 

 torpedo of wood, connected with glass tubes and wires, torpedo- 

 and covered with a piece of sheep skin leather. The 

 difference, however, between the shock given through 

 this torpedo, by means of the charge of a battery, in 

 air, and in water, was too great, and therefore Mr Ca- 

 vendish substituted thick leather for the wood. This 

 instrument was almost an exact imitation of the real 

 torpedo. In air, the shock was felt chiefly in the el- 

 bows, whereas under water it was felt chiefly in the 

 hands. A weaker shock, but one of the same kind, was 

 experienced when Mr Cavendish, instead of touching 

 his artificial torpedo, held his hands under water at two 

 or three inches distance from it. When this torpedo 

 was touched below water with only one hand, a shock 

 was experienced as strong as if it had been touched by 

 both. When it was touched below water with two me- 

 tallic spoons, it gave no shock, but in the air it was 

 very strong. 



Mr Cavendish was likewise able to imitate the tor- 

 pedo in its power of giving a shock to those who 

 trample upon it with shoes on their feet, and when 

 it is buried in sand ; but he could not sufficiently 

 explain the remarkable fact stated by the fishermen, that 

 they often received a shock through their nets when 

 the fish was 12 feet distant from their hands. As it 

 is necessary to suppose that the torpedo is provided with 

 a large battery, Mr Cavendish has endeavoured to com- 

 pute its magnitude in the torpedo examined by Mr 

 Hunter. Mr Cavendish's battery was composed of 49 

 jars of very thin glass, and appears to have contained 

 about 76 feet of coated surface ; and he calculates that 

 the torpedo alluded to could contain 14 times as much 

 electricity as this battery, or was equal to 1064 feet of 

 coated glass. 



Mr Nicholson has followed Mr Cavendish, with much 

 ingenuity, in explaining the anomalous phenomena of 

 the torpedo, by the principles of common electricity ; 

 but we cannot find room for prosecuting this subject 

 any farther. Remarks on 



Wken the Galvanic or Voltaic pile was discovered, tlle use <* 

 philosophers imagined that they would find a striking ' hc (1 e f lc t ^ i( 

 analogy between its action and that of the torpedo, as J 



