ELECTRICITY. 



473 



Bwcriptiv* touched by the finger, a sensation resembling numb- 

 Electricity. ness was immediately experienced. 

 ^""V"" Kaempfer, in his Amcenitates Exoticw, pubh'shed in 

 1702, has given a good description of the effects of the 

 torpedo ; and without imagining them to be similar to 

 those of electricity, he compares them to the effects of 

 lightning. He states, however, that the benumbing in- 

 fluence could be evaded if the person held in his breath, 

 a circumstance which Mr Walsh afterwards found to be 

 correct. 



Dr Bancroft was the first philosopher who suspected, 

 that an analogy existed between the effects of the tor- 

 pedo and those of electricity, and he has mentioned this 

 Walsh's ex- supposition in his Natural History of Guiana. Mr 

 periments, Walsh, however, had the merit of ascertaining this 

 nhen the important point ; and in his valuable paper on the 

 torpedo was torpedo, he has made us acquainted with the leading 

 placed in properties of that singular animal. In order to verify 

 the suspected resemblance between the torpedo and the 

 Leyden phial, Mr Walsh placed a live torpedo upon a 

 table covered with a wet napkin, around which stood five 

 persons insulated. Two brass wires, each 13 feet in 

 length, were suspended to the ceiling by silken strings. 

 The extremity of one of them was placed on the wet 

 napkin, while its other extremity was immersed in a 

 basin full of water placed on a second table, on which 

 stood four other basons full of water. The first person 

 plunged a finger of one hand in the basin in which the 

 wire communicating with the wet napkin was immer- 

 sed, and a finger of the other hand into the second ba- 

 sin. The second person put a finger of one hand in this 

 last basin, and a finger of the other hand into the third 

 basin ; and so on in succession, till the five persons com- 

 municated with one another by the water in the basons. 

 The extremity of the second wire was immersed in the 

 last bason of all ; and Mr Walsh having taken the other 

 end of this wire in his hand, touched the back of the 

 torpedo, when all the five persons experienced a com- 

 motion, which differed only in force from that produced 

 by the Leyden phial : Mr Walsh being out of the cir- 

 cuit, received no shock. This experiment was repeat- 

 ed frequently with the same result, even when eight 

 persons were in the circuit. In other experiments, the 

 shock of the torpedo was communicated through iron 

 wires, and a great many other conductors ; and it was 

 found to be incommunicable through air, glass, and 

 other electrics. Mr Walsh was never able to produce 

 an electric spark, nor to communicate any electricity to 

 the pith balls of the electrometer. 



In general, the shock of the torpedo is not sensible 

 beyond the touching finger; and out of 200 shocks, on- 

 ly one extended above the elbow. When the torpedo 

 was insulated, it was able to give 40 or 50 shocks with- 

 out any diminution of force to persons likewise insula- 

 ted. Every shock of the animal is attended with a de- 

 pression of its eyeg, by means of which Mr Walsh ob- 

 served its attempts to give them even to non-conduc- 

 tors. 



When the These experiments having been made solely in air, 

 torpedo wai Mr Walsh wai anxious to examine its effects in water. 

 I>ld m ; j\ jju-gp torpedo, very prolific in shocks, wag held in 

 both hands by his electric organs above and below, and 

 was then suddenly plunged a foot under water, and in- 

 stantly raised to the same height in the air. This ope- 

 ration was continued for a minute. The moment his 

 lower surface touched the water in descending, he al- 

 ways gave a violent shock, and the moment that surface 

 quitted the water upon its ascent, a still more violent 

 shock was experienced. Both of these .shocks, but par- 



TOL. VIII. PART II. 



water. 



ticularly the last, were always accompanied with a wri- 

 thing in his body, as if he was anxious to make his es- 

 cape. When the animal was wholly in the air, he al- 

 most always gave two shocks, and constantly one, and 

 sometimes two, when he was below water. The in- 

 tensity of the shock under water was scarcely one-fourth 

 of that at the surface, and not much more than one- 

 fourth of those given in the air. The number of shocks 

 appeared to be about 20 in a minute. 



Mr Walsh next put the torpedo into a flat basket, open 

 at the top, but secured by a net with wide meshes, and 

 in this state the animal was let down about a foot into 

 the water. When it was now touched through the 

 meshes with only a single finger on one of its electric 

 organs, while the other hand was held at a distance in 

 the water, he gave shocks which were distinctly felt in 

 both hands. When the circuit for the passage of the elec- 

 tricity was contracted to the finger and thumb of one 

 hand, the finger being applied above, and the thumb 

 below, to a single organ, a shock was experienced twice 

 as great as that which was received when the two arms 

 formed the circuit. 



When the torpedo in the basket was raised to within 

 three inches of the surface of the water, and was then 

 touched with a short iron bolt held in one hand, half 

 out and half in the water, while the other hand was 

 dipped into the water at a distance, strong shocks pas- 

 sing through the iron bolt were experienced in both 

 hands. When the communication between the bolt 

 and the hand was made by a wet hempen cord, the 

 shock was conveyed as before. 



When a powerful torpedo was suspended in a net, 

 and frequently dipped into water, as already described, 

 slight shocks were communicated through the net to 

 the persons that held it. 



In order to explain the difference between the elec- 

 tricity of the torpedo and the Leyden phial, Mr Walsh 

 observes, that the same quantity of electricity will pro- 

 duce very different effects, according as it is used in a 

 dense or a rare state. A small phial, with a coated sur- 

 face of six square inches, will be able to force its charge 

 through an inch of air, and exhibit attraction and re- 

 pulsion, as well as the electric snap and the electric 

 spark. But if this same quantity of electricity is diffu- 

 sed over two large connected jars with a coated surface, 

 with an area 400 times larger than that of the phial, it 

 will exhibit the effects of the torpedo. The charge in 

 this diluted state will not pass through the hundredth part 

 of an inch of air, it will even refuse to pass through the 

 minute interruption in the strip of tinfoil ; the spark 

 and snap, and the approach and recession of light bo- 

 dies, will no longer be produced ; a point brought near 

 will not be able to draw off the charge, and yet in this 

 attenuated state it will run through a considerable circuit 

 of conducting bodies, and during its passage will make 

 us sensible of its impulse. 



A number of experiments on the torpedo were made 

 at Leghorn by Dr Ingenhouz, in 1773. His results 

 were nearly the same as those obtained by Mr Walsh. 

 He describes the shocks or tremors, as giving the same 

 sensation as if a great number of very small electrical 

 bottles were discharged through his hand very quick- 

 ly one after another. Sometimes he found the shock 

 very weak, and at other times it was so strong that he 

 was nearly obliged to quit his hold of the animal. When 

 he pinched the fish with his naita, it did not give more 

 or fewer shocks than when it was not pinched ; but by 

 folding his body, or by bending his right side to his 

 left side, he experienced the shocks more frequently. 



3 o 



Destriptive 

 Electricity. 



Walsh's ex- 

 perimenti 

 on the tor- 

 pedo. - 



Dr Ingen- 

 houz's expe- 

 riment*. 



