ELECTRICAL FISHES.] 



UNDULATORY FORCES. ELECTRICITY. 



185 



number of persons may readily take a shock simultane- 

 ously (if the jar be large enough), by joining hands, and 

 by the last person at each end respectively touching, one 

 the knob of the inside, and the other the outer coating 

 of a charged jar. A convenient way of doing this, is 

 illustrated in the following engraving. 

 Fig. 35. 



By this mode, one person holds a wire proceed- 

 ing from the outside coating of the jar : the last 

 person in the series, holds the wire which is at- 

 tached to the discharger ; and an assistant connects it 

 with the knob of the charged jar, and so gives the 

 shock. 



Individuals vary much with respect to their suscepti- 

 bility of electric shocks. If several persons take a 

 shock together, those having a moist skin on the hands 

 will feel it most acutely. If, however, a shock be 

 taken so that it may pass over the whole body, then the 

 moisture on the skin diminishes the pain by making 

 the body a better conductor. Persons with a harsh, dry 

 skin, feel a shock, with a number of persons, less than 

 they do when taking it singly ; and owing to this, a few 

 persons having a dry skin, placed amongst others, will 

 retard and diminish the effect on those with whom they 

 may be joiued by the hands. For that reason, the 

 hands are sometimes wetted to improve the conducting 

 power. We have frequently taken, whilst in a violent 

 perspiration, with impunity, a two-inch spark from the 

 hydro-electric ; and have also been amused at others, 

 whose skin was entirely dry, calling out, in severe pain, 

 with a shock of the same intensity, which they were in- 

 duced to try from observing its trifling effect on our- 

 selves. 



Considerable care should be observed in giving an 

 electric shock, in any form, to females and young chil- 

 dren, as one too severe might be productive of serious 

 injury, in consequence of its effect on the nervous 

 system. A half-pint charged jar is quite large enough 

 for one person ; whilst one from a quart to three pints 

 capacity, will give a strong shock to twenty or more 

 persons joining hands togetln-r. 



Electricity, in the shape of sparks, was, at one time, 

 in high favour in medical circles, for relieving acute 

 pain in neuralgia and nervous complaints generally ; 

 and, at its first application, like all other novelties, it 

 was held out as a panacea for "all the ills that flesh is 

 heir to. " In the present day, the coil machine (which 

 we shall describe in a future page) is chiefly employed 

 for that purpose, because it is easily set into action, and 

 the strength of the shock, which may be continued for 

 any length of time, is entirely under control. 



There is no doubt that electricity, in animal bodies, is 

 an active agent in sustaining life. The nerves and the 

 muscles are not only affected thereby, but always ex- 

 hibit a current of electricity if proper means be employed 

 to detect it. This is a subject, however, on which we 

 shall have to expand hereafter, as it more particularly 

 belongs to that of voltaic electricity. 



I'J'-ctrical Fishes. Some animals can set free from their 

 bodies, spontaneously, a large amount of electricity : 

 amongst these are the torpedo, the yymnotua efecfricus, 

 and the silunu elettriciu. 



Each of these fishes has the power of giving an electric 



VOL. I. 



Fig. 36. 



shock. The torpedo is a native of Europe ; and its 

 electric organs are placed in its body in a manner which 

 is analogous to the arrangement of a Leyden jar ; for the 

 shock is obtained by placing one hand on the belly, and 

 the other on the back of the fish. 



The gymnotu* is a fish of the 

 eel kind, and is chiefly found in 

 the rivers of South America. 

 It has a very powerful effect on 

 other animals, and can not only 

 stun them, but even destroy 

 life by its shock. One of these 

 was exhibited, some years ago, 

 at the London Polytechnic. It 

 was about three feet long, and 

 was kept in a circular tank of 

 water. Two wires were laid 

 inside ; and these extended to sJ 

 the outside of the tank, and 

 ended in two basins of water. 

 If the hands were dipped in 

 the basins, a powerful shock 

 was experienced, about equal 

 to that of a fully-charged 

 half-pint Leyden jar. The 

 strength of the shock varied, 

 however, from day to day, ac- 

 cording to the activity of the 

 fish. 



The tilurus ekctficus is a 

 native of Africa, and is an in- 

 habitant of swamps, <tc. Its 

 shock is similar to that of the 

 Gymnotus, but its natural his- 

 tory is not so well known. 



lu the annexed engraving, a 

 representation of the various 

 internal organs of the gymnotua 

 electricut will be observed. 



CHEMICAL EFFECTS. 



THE chemical effects produced by f fictional electricity 

 are so feeble as to be scarce worthy of notice, 

 wi-ro it not that they complete a chain of analogy 

 with similar results produced on a much largrr sr.-ilr 

 by other modes of developing the electric force. This 

 is owing to the fact, that electricity obtained by fric- 

 tion, has great intensity or power of overcoming ob- 

 stacles presented by bad conductors, such as the air, 

 <tc. ; but has little or no quantity, or that which would 

 tend to act on a large surface or mass energetically. A 

 few plates of zinc and copper, arranged as a voltaic 

 battery, rapidly decompose water which has been 

 rendered a better conductor by the addition of some 

 sulphuric acid ; whereas, pure water, wlu'ch would 

 scarcely be acted on by voltaic electricity, must bo 

 employed for the purpose of decomposition by electricity 

 obtained by friction. 



The mode usually adopted for this end, is that of 

 employing two gold wires, the extreme points of which 

 are alone exposed to the liquid. A continuous current from 

 a large plate machine, the conductor of which is connected 

 with one wire, may be used ; the other gold wire is to 

 be connected with the earth ; and so a continued current 

 passes between the points of the wires, which should be 

 near to each other. Minute bubbles of gas will be seen 

 to rise, which are those of oxygen and hydrogen. The 

 process is extremely slow, difficult of pursuit, and re- 

 quires care in the entire arrangement. Minute quan- 

 tities of metallic solutions, such as of sulphate of copper, 

 have been decomposed by the action of the hydro- 

 electric machine, which was evidenced by the deposition 

 of metallic copper on one of the wires. Feeble, but 

 decided evidence has been adduced, that the gymniJux 

 el'-ctricui has the power of decomposing water a result 

 which, we believe, was first obtained by Dr. Faraday. 

 This fact goes to prove the identity of the electricity 

 obtained from the fish, with that produced by friction. 



2 B 



