TORPEDO, the CRAMP FISH. See RAJA. The surprising property of this fish in giving a violent shock to the person who takes it in his hands, or
who treads upon it, was long an object of wonder. For some time it was in general reckoned to be entirely fabulous; but at last the matter of fact being ascertained beyond a doubt, philosophers endeavoured to find out the cause. M. Reaumur resolved it into the action of a vast number of minute muscles, which by their accumulated force gave a sudden and violent stroke to the person who touched it. But solutions of this kind were quite unsatisfactory, because the stroke was found to be communicated through water, iron, wood, &c. When the phenomena of electricity began to be better known, it was then suspected that the shock of the torpedo was occasioned by a certain action of the electric fluid; but as not the least spark of fire, or noise, could ever be perceived, this too seemed insufficient. Of late, however, Mr Walsh has with indefatigable pains, not only explained this surprising phenomenon on the known principles of electricity, but given a demonstration of his being in the right, by constructing an artificial torpedo, by which a shock resembling that of the natural one can be given.
The electric organs of the torpedo consist of two sets of very small cylinders lying under the skin, one of which is electrified positively and the other negatively, seemingly at the pleasure of the fish. When a communication is made between the set of cylinders positively electrified, and those which are negatively so, a discharge and shock ensue, like what happens in the case of the Leyden vial. The only difficulty now is to account for the total absence of a spark, (which in the case of the torpedo never exists even in the smallest degree,) and the impossibility of conducting the shock through the smallest interval of air. But this also is explained in a satisfactory manner by Mr Walsh, and shown to be nothing else than what every day takes place in our electrical experiments. It is well known, that a small charge of electricity, if put into a little vial, will occasion a bright spark and loud noise when discharged. But if the same charge is put into a vial much larger, the spark and noise will be less in proportion; neither will the spark break through near such a space of air in the latter case as in the former; though the shock would in both cases be the same to a person who received it through his body. If, instead of a large vial, we suppose the charge to be diffused all over a large battery, the shock would still be the same, and yet the spark and noise attending it would be almost imperceptible. The case is just the same with the torpedo. Each of the electric organs is a battery composed of innumerable small cylinders, which discharging themselves all at once produce a formidable shock; but by reason of the smallness of the charge of each, the spark is imperceptible, and cannot break through the smallest space of air. The truth of this was exemplified in Mr Walsh's artificial torpedo, which though it would give a very considerable shock through a conductor totally uninterrupted, yet on the least breach therein, even for the breadth of a hair, no shock was felt.
In every other respect the electricity of the torpedo agrees with that exhibited by the common electrical machines. An insulated person cannot receive a shock by touching one of the electric organs of the fish; but a violent stroke is given to the person, whether insulated or not, who lays one hand on the positive and the
the other on the negative organ. The fish, as is reasonable to imagine, seems to have this electric property in its own power, and appears sensible of his giving the shock, which is accompanied by a kind of winking of his eyes.