86 



ANIMAL ELECTRICITY. 



thrust into the electrical organ of a torpedo 

 the two needles which terminate the wires of 

 Schweigger's multiplier, and immediately saw 

 the magnetic needle describe more than half a 

 revolution.* 



V. Chemical effects of the discharge. It 

 does not appear that any observer before Sir 

 H. Davy attempted to ascertain what chemical 

 effects the discharge from electrical fishes is 

 capable of producing. But Sir Humphry 

 obtained only negative results. He passed the 

 shocks of the torpedo through the unterrupted 

 circuit made by the silver wire through water, 

 without being able to perceive the slightest de- 

 composition of the water.f Dr. John Davy, 

 however, has obtained decisive evidence of 

 chemical agency being exerted by animal elec- 

 tricity. The fishes which he made use of in 

 his experiments were more recently taken from 

 the sea, and were, consequently, more vigorous 

 than those which were the subjects of Sir 

 Humphry's observations; and it was, probably, 

 owing to this circumstance that the results which 

 he obtained were different from those of his 

 brother's experiments. 



By means of golden wires, one of which was 

 applied to the upper surface of the fish, and the 

 other to its under surface, Dr. Davy passed the 

 discharge from a torpedo through solutions of 

 nitrate of silver, common salt, and superacetate 

 of lead, and found that all were decomposed. 

 The decomposition of the superacetate of lead 

 was effected only when the fish seemed to put 

 forth all its energy, after being much irritated. \ 

 From the solution of nitrate of silver, the metal 

 was precipitated only on the wire connected 

 with the ventral surface of the fish. When 

 platina wires were used, and plunged into nitric 

 acid, gas was given off only from that in con- 

 nexion with the dorsal surface. A solution of 

 iodide of potassium and starch having been 

 subjected to the discharge conveyed along the 

 platina wires, had the iodine in combination 

 with the starch precipitated from it on the wire 

 from the upper surface. By the same dis- 

 charges which produced these chemical effects, 

 the needle in the galvanometer was moved, the 

 spirit in the air- thermometer was raised, and 

 needles in the spiral were magnetized. 



VI. Results of experiments on the transmis- 

 sion of the discharge through various conduct- 

 ing bodies. Almost all bodies which are con- 

 ductors of common and voltaic electricity con- 

 duct also the discharge of electrical fishes; and 

 those which are non-conductors with regard to 

 the former are the same with regard to the latter. 

 But the discharge of the torpedo, when feeble, 

 does not pass along even good conductors ; and 

 this circumstance has given rise to some dis- 

 crepancy between the statements of different 

 observers. Walsh received the torpedo's dis- 

 charge through iron bolts and wet hempen 

 cords. The French fishermen declare that they 

 sometimes receive shocks through nets, while 



* Pouillet, Elom. de Phys. i. 773. 

 t Phil. Trans. 1829. 

 J Phil. Trans. 1832. 

 $ Phil. Trans. 1834. 



the fish is twelve feet distant from their hands. 

 But Humboldt and Gay Lussac state that they 

 received no shock when they touched the fish 

 with a key or any other conducting body ; * 

 further, that when they placed the fish upon a 

 metallic plate, so that the inferior surface of its 

 electric organ touched the metal, the hand which 

 supported it felt no shock : and they concluded 

 from their experiments that the torpedo could 

 not transmit its discharge through even a thin 

 layer of water ; although they found that when 

 two persons applied each one hand to the fish, 

 and completed a circuit through their own 

 bodies by means of a pointed piece of metal 

 held in the other hand, and plunged into a little 

 water placed upon an insulating body, both 

 felt the shock. In one instance Dr. Davy 

 received the torpedo's shock through water, but 

 his hand was within a very short distance of the 

 fish. Walsh transmitted the torpedo's discharge 

 through a chain of eight persons, who com- 

 municated with one another only by water con- 

 tained in basins, in which their hands were 

 immersed. And the same observer also found 

 that when a torpedo was touched with a single 

 finger of one hand, while the other hand was 

 held in the water at some distance, shocks 

 were distinctly felt in both hands. Numerous 

 observations made on the Gymnotus leave no 

 doubt with regard to the passage of its discharge 

 through water. If a person hold his finger in 

 the water several inches (some say even ten 

 feet) distant from the fish, and another person 

 touch it, both receive shocks equally severe. 

 Dr. Williamson found that a person holding his 

 finger in a stream of water, running from a hole 

 made in the bottom of a wooden vessel in 

 which a Gymnotus was swimming, very dis- 

 tinctly felt all the discharges given by the fish. 

 The discharge from the Gymnotus passes through 

 a chain often persons, so that they all seem to 

 feel the shock in the same degree. It is con- 

 ducted by iron rods several feet in length. It 

 does not pass through air, interposed between 

 metallic conductors, until these are brought 

 within about one-hundredth of an inch of each 

 other. 



So far as they have been examined, the phe- 

 nomena presented by the discharge of the 

 Silurus have been found to be nearly the same 

 as those just detailed. 



VII. The production of a spark, and evolu- 

 tion of heat. No observer has hitherto seen light 

 emitted from the body of any electrical fish at 

 the time of the discharge; but, by artificial 

 arrangements, some have succeeded in pro- 

 ducing sparks in the course of the circuit de- 

 scribed by the discharge. In 1792, Gardini 

 saw a spark from a torpedo's discharge, in 

 the course of his repeating some of Walsh's 

 experiments. And in 1797, Galvani obtained 

 a small spark, visible only with the aid of a 

 lens, from a torpedo ; but it does not appear that 

 any other observer has been equally successful 

 tvith regard to this fish. Very recently, Dr. Davy 

 has directed his attention particularly to this 

 point, and, although he used active fish, and took 



* Ann. de Chimie, t. Ixv. 15. 



