GALVANISM. 



example, into one of the ears of an ox 

 recently killed a finger of one hand, 

 moistened with a solution of salt, and 

 holding in the other hand a prepared 

 frog, when the spine of the frog was 

 made to touch the tongue of the ox, 

 convulsions took place in the limb of the 

 frog. In like manner, when he held a 

 prepared frog by one hand, moistened 

 with solution of salt, and applied the 

 crural nerves of the animal to the tip 

 of his own tongue, convulsions were 

 produced.* Many of these experiments 

 were made in presence of the members 

 of a commission of inquiry appointed by 

 the French Institute: and they have 

 since been repeated with success in 

 London, at the Anatomical Theatre in 

 Great Windmill Street. 



(88.) It is well known that several 

 fishes, such as the torpedo, which is a 

 species of ray ; the gymnotus electricus, 

 or the electric eel ; the silurus electri- 

 cus, a species peculiar to some of the 

 rivers in Africa ; and also the trichiurus 

 indicus, and tetraodon electricus, which 

 are fishes found in the Indian ocean, 

 possess the power of giving electrical 

 shocks to animals that touch them, or 

 communicate with them by electrical 

 conductors. Anatomical investigation 

 has shown that this power resides in 

 organs of a very peculiar construction. 

 In the torpedo they are composed of a 

 great multitude of vertical and parallel 

 membranous plates, arranged in longi- 

 tudinal columns of quadrangular, pen- 

 tagonal, or hexagonal forms, with a loose 

 net-work of tendinous fibres passing 

 transversely and obliquely between the co- 

 lumns, and uniting them firmly together. 

 Each column is, moreover, divided by a 

 great number of thin horizontal parti- 

 tions, placed over each other at very small 

 distances, and forming numerous in- 

 terstices, which appear to contain a 

 fluid. All these parts are supplied by a 

 great abundance of blood-vessels, and 

 by a still more extraordinary proportion 

 of nerves. 



(89.) In the regular arrangement of 

 their plates these organs have a marked 

 resemblance to a voltaic battery; we 

 know nothing, however, of the imme- 

 'diate source "from which they derive 

 electrical properties. Mr. Cavendish 

 compared the action of the torpedo to 

 that of a large electricaljar very weakly 

 charged : and Volta considered it as still 

 more analogous to that of the galvanic 

 pile. Sir Humphry Davy, with a view 



* Nicholson's Journal, iii, 298, 



to ascertain the justness of Volta' s com- 

 parison, passed the shocks given by 

 living torpedos through the interrupted 

 circuit made by silver wire through 

 water, but could not perceive that it pro- 

 duced the slighest decomposition 'of that 

 fluid. The same shocks made to pass 

 through a fine silver wire less than one 

 thousandth of an inch in diameter did 

 not produce ignition. Volta, to whom 

 Sir H. Davy communicated the results 

 of these experiments, considered the 

 conditions of the organs of the torpedo 

 to be best represented by a pile, of which 

 the fluid substance is "a very imperfect 

 conductor, such as honey ; and which, 

 though it communicated weak shocks, 

 yet did not decompose water. Sir H. 

 Davy also ascertained that the electrical 

 shocks given by the torpedo, even when 

 powerful, produced no sensible effect on 

 an extremely delicate magnetic electro- 

 meter. In a paper recently read at the 

 Royal Society, he explains these nega- 

 tive results by supposing that the motion 

 of the electricity in the organ of the tor- 

 pedo is in no measurable time, and wants 

 that continuity of current requisite for 

 the production of magnetic effects. 



(90.) Mr. Geoffrey St. Hilaire has 

 found an organic structure very similar 

 to that of the torpedo in other animals 

 of the ray genus, which, nevertheless, do 

 not possess any electrical powers. 



(91.) Electrical effects are obtained 

 from a pile composed of thin plates of 

 different metals in the usual order, with 

 discs of writing paper interposed between 

 them. This species of pile was the in- 

 vention of Mr. De Luc, who gave it the 

 name of the electrical column. It may 

 be constructed of pieces of paper, silver- 

 ed on one side, by means of silver leaf, 

 and alternated with thin leaves of zinc ; 

 taking care that the silvered surfaces of 

 the paper discs are always in the same 

 direction. A very large number of these 

 may be contained in a glass tube of mo- 

 derate length, previously well dried, 

 having its ends covered with sealing- 

 wax, and capped with brass. The most 

 extensive instrument of this kind was 

 made by Mr. Singer, and consisted of 

 twenty thousand series. Each of the 

 two ends or poles of the column affect 

 the electrometer, and exhibit electrical 

 attractions and repulsions ; the appara- 

 tus will even give sparks, and commu- 

 nicate shocks of considerable force : but 

 it possesses no sensible power of chemi- 

 cal decomposition when applied to fluids 

 in the interrupted circuit. If two 



