Account of the Torpedo. Shaw's British Zoology.

THE

From

This

HE torpedo has been celebrated both by ancients and moderns for its wonderful faculty of causing a sudden numbness or painful sensation in the limbs of those who touch or handle it. power the ancients, unacquainted with the theory of electricity, were contented to admire, without attempting to explain; and, as is usual in similar cases, magnified into an effect little short of what is commonly ascribed to enchantment. Thus we are told by Oppian, that the torpedo, conscious of his latent faculty, when caught by a hook, exerts it in such a manner that, passing along the line and rod, it benumbs the astonished fisherman, and suddenly reduces him to a state of helpless stupefaction.

It is affirmed by Pliny, that the torpedo, even when touched with a spear or stick, can benumb the strongest arm, and stop the swiftest foot.

It is well observed by Dr. Bloch, that these exaggerations, on the part of the ancients, are the less to be wondered at when we reflect on similar ones in modern times. Thus when Muschenbroek happened accidentally to discover and feel the effect of the electric shock from what is called the Leyden phial, he representedit of so terrible a nature as to affect his health for several days afterwards, and declared that he would not undergo a second for the whole kingdom of France. Yet this is now the common amusement of philosophical curiosity.

The observations of the learned Redi and others of the seventeenth century, had tended, in some degree, to elucidate the peculiar actions and anatomy of the torpedo ; but it was reserved for more modern times, and for our own ingenious countrymen in particular, to exthe particulars of its history; and plain in a more satisfactory manner to prove that its power is truly electric. The first experiments of this kind were made by Mr. Walsh, of the royal society of London, at Rochelle in France, in the year 1772.

"The effect of the torpedo," says Mr. Walsh, "appears to be absolutely electrical forming, its cir. cuit through the same conductors

with electricity, and being intercepted by the same non-conductors as glass and scaling-wax. The back and the breast of the animal appear to be in different states of electricity, I mean in particular the upper and lower surfaces of the two assemblages of pliant cylinders engraved in the works of Lorenzini*. By the knowledge of this circumstance we have been able to direct his shocks, though they were small, through a circuit of four persons, all feeling it, and likewise through a considerable length of wire held by two insulated persons, one touching his lower surface and the other his upper. When the wire was exchanged for glass or sealing wax no effect could be obtained; but as it was resumed the two persons became liable to the shock. These experiments have been varied many ways, and repeated times without number, and they all determined the choice of conductors to be the same in the torpedo as in the Leyden phial. The sensations likewise, occasioned by the one and the other in the human frame, are precisely similar. Not only the shock, but the numbing sensation, which the animal sometimes dispenses, expressed in French by the words engourdissement and fourmillement, may be exactly imitated with the phial, by means of Lane's electrometer; the regulating rod of which, to produce the latter effect, must be brought almost into contact with the prime conductor which joins the phial. It is a singularity that the torpedo, when insulated, should be able to give us, insulated likewise, forty or fifty successive shocks from nearly

the same part; and these with lit tle, if any diminution of their force. Each effort of the animal to give the shock is conveniently accompanied by a depression of his eyes, by which even his attempts to give it to non-conductors can be observed: in respect to the rest of his body he is in a great degree motionless, though not entirely so. I have taken no less than fifty of the abovementioned successive shocks from an insulated torpedo in the space of a minute and a half. All our experiments confirm that the electricity of the torpedo is condensed, in the instant of its explosion, by a sudden energy of the animal; and as there is no gradual accumulation, or retention of it, as in case of charged glass, it is not at all surprising that no signs of attraction or repulsion were perceived in the pith balls.

In short, the effect of the torpedo appears to arise from a compressed elastic fluid, restoring itself to its equilibrium in the same way, and by the same mediums, as the elastic fluid compressed in charged glass. The skin of the animal, bad conductor as it is, seems to be a better conductor of his electricity than the thinnest plate of elastic air. Notwithstanding the weak spring of the torpedinal clectricity, I was able, in the public exhibitions of my experiments at La Rochelle, to convey it through a circuit formed from one surface of the animal to the other, by two long brass wires, and four persons, which number, at times, was increased even to eight. The several persons were made to communicate with each other, and the two outermost with the wires, by

means

means of water contained in basons, properly disposed between them for that purpose. This curious and convincing experiment is thus related by Monsieur Seignette, mayor of La Rochelle, and one of the secretaries of its academy; published in the French gazettes, for the month of October in the above year.

A live torpedo was placed on a table round another table stood five persons insulated: two brass wires, each thirteen feet long, were sus pended to the ceiling by silken strings. One of these wires rested by one end on the wet napkin on which the fish lay; the other end was immersed in a bason full of water, placed on the second table, on which stood four other basons likewise full of water. The first person put a finger of one hand in the bason in which the wire was immersed, and a finger of the other hand in a second bason. The second person put a finger of one hand in the last bason, and a finger of the other in a third, and so on successively, till the five persons communicated with one another, with the water in the hasons. In the last bason one end of the second wire was immersed, and with the other end Mr. Walsh touched the back of the torpedo, when the five persons felt a commotion which differed in nothing from that of the Leyden experiment, except in the degree of force. Mr. Walsh, who was not in the circle of .conduction, received no shock. This experiment was repeated several times, even with eight persons, and always with the same success. The action of the torpedo is communicated by the same medium as the electric fluid. The bodies which intercept the action of the one intercept likewise the action of the other.

The effects produced by the torpedo resemble in every respect a weak electricity.

This exhibition of the electric powers of the torpedo, before the academy of La Rochelle, was at a meeting held for the purpose, in my apartments, on the 22d of July, 1772, and stands registered in the journals of the academy."

Mr. Walsh, in his paper on this subject, in the Philosophical Transactions, thus continues the account of these interesting experiments :

"The effect of the animal, in the above experiments, was transmitted through as great an extent, and variety of conductors, as almost at any time we had been able to obtain it, and the experiments included nearly all the points in which its analogy with the Leyden phial had been observed. These points were stated to the gentlemen present, as were the circumstances in which the two effects appeared to vary. It was likewise represented to them, that our experiments had been almost wholly with the animal in air; that its action in water was a capital desideratum, that indeed all as yet done was little more than opening the door to inquiry; that much remained to be examined by the electrician, as well as the anatomist: that as artificial electricity had thrown light on the natural operation of the torpedo, this might, in return, if well consi dered, throw light on artificial electricity, particularly in those respects in which they now seemed to differ. The torpedo, in these experiments, dispensed only the distinct, instantaneous stroke, so well known by the electric shock. That protracted but lighter sensation, that torpor or numbness which he at times induces, and from which he takes his name,

was not then experienced from the animal, but it was imitated with artificial electricity, and shewn to be producible by a quick consecution of minute shocks. This, in the torpedo, may perhaps be effected by the successive discharge of his numerous cylinders, in the nature of a running fire of musquetry: the strong single shock may be his general volley. In the continued effect, as well as the instantaneous, his eyes, which are usually prominent, are withdrawn into their sockets.

"A large torpedo, very liberal of his shocks, being held with both hands, by electric organs above and below, was briskly plunged into water to the depth of a foot, and instantly raised an equal height in air, and was thus continually plunged and raised, as quick as possible, for the space of a minute. In the instant his lower surface touched the water in his descent, he always gave a violent shock, and another, still more violent in his ascent; both which shocks, but particularly the Jast, were accompanied with a writhing in his body, as if meant to force an escape. Besides these two shocks from the surface of the water, which may yet be considered as delivered in the air, he constantly gave at least two when in the air, and as constantly one, and sometimes two, when wholly in the water. The shocks in the water appeared, as far as sensation could decide, not to have near a fourth the force of those which took place at the surface of the water, nor much more than a fourth of those entirely in air.

"The shocks received in a certain time were not, on this occasion, counted by a watch, as they had been on a former, when fifty were delivered in a minute and a half, by

2

the animal, when in an insulated and unagitated state; but, from the quickness with which the immersions were made, it may be presumed there were full twenty of these in a minute; from whence the number of shocks in that time must have amounted to above an hundred.— This experiment, therefore, while it discovered the comparative force between a shock in water and one in air, and between a shock delivered with a greater degree of exertion on the part of the animal, and one with less, seemed to determine that the change of his organs with eleetricity, as well as the discharge, was affected in an instant.

"The torpedo was then put into a flat basket, open at the top, but secured by a net with wide meshes, and with this confinement was let down into the water about a foot below the surface; being there touched through the meshes, with only a single finger, on one of his electric organs, while the other hand was held at a distance in the water, he gave shocks which were distinctly felt with both hands.

"The circuit for the passage of the effect being contracted to the finger and thumb of one hand, applied above and below to a single organ, produced a shock, to our sensation, of twice the force of that in the larger circuit by the arms.

"The torpedo, still confined in the basket, being raised to within three inches of the surface of the water, was there touched with a short iron bolt, which was held, half above and half in the water, by one hand, while the other hand was dipped, as before, at distance in the water; and strong shocks, felt with both hands, were thus obtained through the iron.

"A wet

"A wet hempen cord, being fastened to the iron boit, was held in the hand above the water, while the bolt touched the torpedo, and the shocks were obtained through both these substances.

"A less powerful torpedo, suspended in a small net, being frequently dipped into water, and raised again, gave, from the surface of the water, slight shocks through the net to the person holding it,

"These experiments in water manifested, that bodies immersed in that element might be affected by immediate contact with the torpedo; that the shorter the circuit in which

the electricity moved, the greater would be the effect; and that the shock was communicable, from the animal in water, to persons in air, through some substances.

"How far harpoons and nets, consisting of wood and hemp, could in like circumstances, as it has been frequently asserted, convey the effect, was not so particularly tried, as to enable us to confirm it. I mention the omission, in hopes some one may be induced to determine the point by express trial.

"We convinced ourselves, on former occasions, that the accurate Kampfer, who so well describes the effect of the torpedo, and happily compares it with lightning, was deceived in the circumstance that it could be avoided by holding in the breath, which we found no more to prevent the shock of the torpedo, when he was disposed to give it, than it would prevent the shocks of the Leyden phial.

"Several persons, forming as many distinct circuits, can be affected by one stroke of the animal, as well as when joined in a single circuit. For instance, four persons touching separately his upper and lower sur VOL. XLVI.

faces, were all affected; two persons likewise, after the electricity had passed through a wire into a bason of water, transmitted it from thence into two distinct channels, as their sensation convinced them, into another bason of water, from whence it was conducted, probably in an united state, by a single wire. How much farther the effect might thus be divided and subdivided into different channels, was not determined; but it was found to be proportionately weakened by multiplying these circuits, as it had been by extending the single circuit."

The body of the torpedo is of a somewhat circular form, perfectly smooth, slightly convex above, and marked along each side of the spine by several small pores or foramina: the colour of the upper surface is usually a pale reddish brown, sometimes marked by five, large, equidistant, circular dusky spots, with paler centres; the under surface is whitish, or flesh-coloured. The torpedo, however, is observed to vary considerably in the cast and intensity of its colours. The general length of the torpedo seems to be about eighteen inches, or two feet, but it is occasionally found of far larger dimensions, specimens having been taken on our own coasts of the weight of fifty, sixty, and even eighty pounds. A specimen, weighing fifty-three pounds, was found, according to Mr. Pennant, to measure four feet in length, and two and a half in breadth: the head and body, which were indistinct, were nearly round, about two inches thick in the middle, attenuating to extreme thinness on the edges: below the body, the ventral fins formed on each side one fourth of a circle: the two dorsal fins were placed on the trunk of the tail: the eyes were small, placed near each 3 F

other: