Experiments on the Torpedo.

By Meſſrs. Humboldt and Gay Lussac.

Extracted from a Letter of M. Humboldt to M. Berthollet; dated Rome, 15 Fructidor, Year 13 ( Sept. 2, 1805.)

Annales de Chimie, Vol. LVI.

The curious theory with which Volta has enriched the ſcience of natural philoſophy, on the ſubject of electric fiſh having been received as authentic by many naturaliſts, renders the phenomenon of the Torpedo worthy of farther inveſtigation.

You know, my dear friend, what was our impatience to procure theſe fiſh, and will perhaps be ſurpriſed that ſo much time ſhould elapſe without having heard from us on the ſubject.

At Genoa, we perceived ſome; but we were then without our inſtruments.

At Civita Vecchia we ſought them in vain.

But during our ſtay at Naples we frequently procured ſome very large and lively ones.

In this letter you will find detailed the experiments made by M. Gay-Luſſac and myſelf on the powers of this fiſh (Raja-torpeda of Linneus). M. de Buch, a German mineralogiſt, well acquainted with all the branches of phyſical ſcience, was witneſs to our proceedings.

I ſend you the reſults, giving ſimple facts, unmixed with theoretical ſpeculations.

Our experiments were chiefly directed towards the diſcovery of that ſtate of the torpedo when it was leaſt capable of exerting its power upon the human frame.

This power has been generally deſcribed as electrical; but the ſenſation produced by it is materially different from that cauſed by the diſcharge of a Leyden phial.— Having no other book by us beſides the work wherein Aldini combines the reſearches of Geoffroy with thoſe of Spallanzani and Galvani, it is not to be expected that we ſhould compare our experiments with thoſe which may have been previouſly made by other philoſophers.

The torpedo found at Genoa and Naples, but not at Civita Vecchia.

The ſhock of the torpedo feels different from that of electricity.

Memoires ſur la Torpille, dans l’Eſſai ſur le Galvaniſm, Vol. II. p. 61.

1. Though the ſtrength of the torpedo is far inferior to that of the gymnotus, it is equally capable of cauſing painful ſenſations.

A perſon much accuſtomed to electric ſhocks, can hardly ſuſtain that of a lively torpedo of four decimeters (16 inches) in length.

The animal acts under water, and it is only when it loſes ſtrength that the fluid impedes its action.

Powers of the torpedo inferior to thoſe of the gymnotus of S. America.

Shock of the torpedo more violent than that of electricity.

It acts under the water,

In this caſe, M.

Gay Luſſac obſerved that the ſhock is not perceptible till the fiſh is raiſed above the ſurface.

2. I obſerved, when in South America, that the gymnotus gives the moſt violent ſhocks, without any exterior movement of the eyes, the head, or the fins: it appeared as tranquil as a perſon when paſſing from one idea to another, or from one ſenſation to another.

Not ſo the torpedo:

We obſerved a convulſive movement of the pectoral fins, each time it gave a ſhock, which was more or leſs violent according as the ſurface was larger or ſmaller wherein the contact took place.

—and ſeems to uſe more effort than the gymnotus.

3. The powers of the torpedo and gymnotus cannot be excited at pleaſure, as we ſhould diſcharge a Leyden phial or a conductor.

A ſhock is not always felt on touching an electric fiſh; it muſt be irritated before it will give the ſhock.

This action depends on the will of the animal, whoſe electric powers perhaps, are not kept conſtantly charged; yet it can recover them with wonderful celerity, as it is capable of giving a long ſucceſſion of ſhocks.

Shocks from the torpedo and gymnotus cannot be obtained but by irritating the animal.

The ſhock obtained by a mere touch with the finger,

4. The ſhock is felt (the animal being diſpoſed to give it) as well on touching with one finger a ſingle ſurface of the electric organs, as on applying the two hands to the two ſurfaces, the upper and under, at once.

In both caſes it is immaterial whether the perſon applying his finger or his two hands, be inſulated or not.

—but the contact muſt be direct.

Metals ſeem to be non-conductors of the ſhock of the torpedo.

5. When an iſolated perſon touches the torpedo with a ſingle finger, it is indiſpenſible that the contact be immediate, as no ſhock will be felt if a conducting body (of metal for example) be interpoſed between the finger and the organ of the fiſh.— For this reaſon, the animal may be touched with impunity by means of a key, or any other inſtrument of metal.

6. M. Gay-Luſſac having made this important obſervation, we placed a torpedo on a metal diſh, with which the inferior ſurface of its organs were in contact.

The hand which ſupported this diſh experienced no ſhock, whilſt another iſolated perſon irritated the animal, whoſe convulſive movement of the pectoral fins indicated a moſt violent emiſſion of the electric fluid.

Experiments which ſhew that they conduct.

7. When on the contrary, a perſon held the torpedo in a metal diſh in his left hand (as in the preceding experiment), and with his right touched the ſuperior ſurface of the electric organ, he experienced a ſmart ſhock in both arms at the ſame moment.

8. The ſame was felt, on placing the fiſh between two metal plates, whoſe edges were not in contact with each other, and applying the two hands at once above and below them.

9.

But if the edges of the metal plates be ſuffered to touch each other, no ſhock will be felt in either arm.

The communication between the two ſurfaces of the organs is, in this caſe, formed by the plates; and the new connection ariſing from the contact of the two hands with the plates is without effect.

The organs of the torpedo have no influence on the electrometer.

10. The moſt ſenſible electrometer manifeſted no electrical tenſion in the organs of the torpedo; in whatever way it was applied, it was not in the leaſt affected; neither, on directing it towards the organs, nor in inſulating the fiſh, covering it with a metallic plate, and making a communication between this plate, by means of a conducting thread, and the condenfer of Volta, was there any indication (as with the gymnotus) that the animal affected the electric intenſity of ſurrounding bodies.

11. As electric fiſh, when healthy, exerciſe their powers as forcibly beneath the water as in the open air, we were led to examine the conducting properties of this fluid.

Several perſons formed a chain of hands between the ſuperior and inferior ſurfaces of the organs of the torpedo: the ſhock was not felt until they had wetted their hands.

The action was not intercepted when two perſons ſupported the torpedo with their right hands; and inſtead of holding each other’s left hand, they each plunged a metallic rod into water placed upon an iſolated body.

Examination of the conducting powers of water.

12. By ſubſtituting flame in lieu of water, the communication was deſtroyed, until the rods touched each other in the flame.

Flame does not conduct the ſhock.

13. It muſt, however, be obſerved, that in water, as in air, the ſhock was not perceptible without an immediate contact with the body of the electric fiſh: the leaſt poſſible intervention of the water prevented it.

This fact is the more remarkable, as it is known that in galvanic experiments, where the frog is immerſed in water, it is ſufficient to direct the ſilver forceps towards the muſcles to cauſe a contraction, though a body of water be interpoſed, equal to one or two millimetres in thickneſs, or about one-twentieth of an inch.

No ſhock can be obtained without immediate contact with the fiſh.

Theſe, my dear friend, are the principal obſervations which we have made on the torpedo.

The experiments, No. 4 and 10, prove that the electric organs of theſe animals are not ſuſceptible of any intenſity or exceſs of charge.

Their action may rather be compared to that of a combination of Leyden phials, than to the conductor of Volta.

Without communication no ſhock could be felt: and having experienced the power of the gymnotus through very dry cords, I imagine, that where I have been affected by this powerful animal without direct contact, it had been occaſioned by ſome deficiency in my inſulated ſtate.

If the torpedo act by poles, that is by an electric equilibrium which poſſeſſes a tendency to repleniſh itſelf, experiments 5 and 6 ſeem to prove that theſe poles exiſt near each other, on the ſame ſurface of the organ.

The ſhock is felt on merely touching the ſurface with the finger.

A plate interpoſed between the hand and the organ, (Exp. 6,) re-eſtabliſhes the equilibrium, and the hand which ſuſtains the plate is not affected, becauſe it is placed beyond the current.

But if we ſuppoſe an heterogeneous number of poles upon each ſurface of the organ, whence does it ariſe, that, in covering theſe ſurfaces with two metal plates, whoſe edges do not touch each other, and placing the hands on theſe plates, the equilibrium ſhould be found in the arms?

Why, it may be aſked, does not the poſitive electricity of the inferior ſurface ſeek at the moment of exploſion the negative electricity of the next or neareſt pole, but rather ſeek it in the ſuperior ſurface of the electric organ?

Perhaps theſe difficulties may not be inſurmountable; yet the theory of theſe vital actions well deſerves attentive reſearch.

Geoffroy has proved that thornbacks, who give no ſigns of electricity, are furniſhed with organs analogous to thoſe of the torpedo.

The leaſt injury on the brain of the torpedo deſtroys its electric powers.

The nerves are no doubt concerned chiefly in theſe phenomena; and the phyſiologiſt who ſhould admit the power of vital actions, might with ſucceſs oppoſe the theory of the naturaliſt, who would endeavour to explain all by the contact of the albumino-gelatinous pulp of the nervous laminæ wherewith nature has endowed the organs of the torpedo.

Organs of the torpedo not ſuſceptible of any exceſs of charge.

Doubt whether the ſhock of the gymnotus can be felt without actual contact with it.

Torpedo ſuppoſed to act by an electric equilibrium, the oppoſite ſtate being very near.

Objections to this notion.

Conſiderations of theory.