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 laminae 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.