An account of some experiments and observations on the torpedo

Abstract

The late Sir Humphry Davy gave an account, in a paper published in the Philosophical Transactions for 1829, of some experiments which he made on the Torpedo, with the view of ascertaining how far its electricity is analogous to that of the voltaic, or other galvanic batteries; but the results he obtained were altogether of a negative kind. He was prevented by the declining state of his health from prosecuting this inquiry, which he was still ardently bent upon completing, and which he requested his brother would carry on after his death. The author, accordingly, when at Malta, being in a favourable situation for obtaining living torpedos, made the series of experiments which are related in the present paper. They entirely confirm those of Mr. Walsh made in 1772, and which established the resemblance of the agency exerted by this fish to common electricity; and they also prove that, like voltaic electricity, it has the power of giving magnetic polarity to steel, of deflecting the magnetic needle, and also of effecting certain chemical changes in fluids subjected to its action. Needles perfectly free from magnetism were introduced within a spiral coil of copper wire, containing about 180 convolutions; the whole coil being an inch and a half long and one tenth of an inch in diameter, weighing only four grains and a half, and being contained in a glass tube just large enough to receive it. On the electric discharges from a vigorous torpedo being made to pass through the wire during a few minutes, the needles were rendered strongly magnetic. The same influence transmitted through the wires of the multiplier produced very decided deflexion of the needle; the under surface of the electrical organ of the torpedo corresponding in its effect to the zinc plate of the simple voltaic circle, and the upper surface corresponding to the copper plate. No effect of ignition could be perceived when the discharge from the torpedo was made to pass through a silver wire one thousandth of an inch in diameter: nor could unequivocal evidence be obtained of the production of sparks on interrupting the circuit; the slight luminous appearances which occurred being probably of the same kind as those often exhibited by sea water when agitated. A small gold chain, however, composed of sixty double links, was found to be capable of transmitting the shock; a fact which seems to show that air is not impermeable to the electricity of the torpedo. When fine silver wires, interrupted by a solution of common salt, were placed in the circuit, minute bubbles of air collected round the point communicating with the under side of the torpedo, but none at the other point. When gold wires, instead of the silver ones, were used, gas was evolved from each of the extremities; but in greatest quantity, and in smaller bubbles, from the lower, than from the upper wire. With a strong solution of nitrate of silver, the point of the lower gold wire became black, and only two or three bubbles arose from it; the point of the upper gold wire remaining bright, and being surrounded with many bubbles. Similar, but less distinct, results were obtained by employing a strong solution of superacetate of lead. The remainder of the paper is occupied with a detailed account of the anatomical structure of the electrical organs of the torpedo, and of the muscles that surround them. The texture of the columnar portions of those organs appears to be homogeneous, with the exception of a few fibres, probably branches of nerves, which pass into them. A large quantity of water, separable by evaporation, enters into their composition: and they undergo spontaneous changes more slowly than the muscles. They are incapable of contraction by any of the ordinary stimuli, and even that of an electric shock from a voltaic battery, applied either to the organs themselves or to the nerves which supply them. Hence the conclusion is drawn that these organs are not muscular, but that their columns are formed by tendinous and nervous fibres, distended by a thin gelatinous fluid.