Instructions for testing the Torpedo Fish, 12 August 1772
Instructions for Testing the Torpedo Fish
ADS and incomplete draft: American Philosophical Society
The role that Franklin played in John Walsh’s experimentation with the torpedo fish cannot be precisely defined because the evidence is missing. Walsh testified to the older man’s encouragement,9 which may have included something akin to the instructions printed below. But these particular instructions, even though they are endorsed by Walsh, could not have guided his investigation; for they are dated a month after he first reported on it.1 An undated and incomplete draft among Franklin’s papers, entitled “Directions to Discover whether the Power that gives the shock, in touching the Torpedo, … is electrical or not,” is an early version of the second and third paragraphs below. In his French edition Dubourg translated and printed this draft, with its title; he then followed it with a second document, which he dated August 12 and which is a verbatim translation of the fourth and fifth paragraphs, and explained that it was an addition Franklin made in the light of Walsh’s report of his findings.2 Did the editor receive the full instructions as printed here? If not, why not? If so, why did he translate part of them and the draft version of another part? Conceivably because that version was what Walsh took with him to France, but this is no more than conjecture. All that can be said with assurance is that the experiments performed by Walsh resembled in many ways those that Franklin suggested.
London, Aug. 12. 1772
It has long been supposed that the Stroke given by the Torpedo was the Effect of sudden violent muscular Motion. It is now suspected to be an Effect of the electric or some similar subtil Fluid, which that Fish has a Power of acting upon and agitating at Pleasure.
To discover whether it be the Effect of a subtil Fluid, or of muscular Motion, let the Fish be touch’d with the usual Conductors of Electricity, viz. Iron or other Metals; and with the known Non-conductors of Electricity, dry Wood, Glass, Wax, &c. If the Stroke be communicated thro’ the first and not thro’ the latter, there is so far a Similarity with the electric Fluid;3 and at the same time a Proof that the Stroke is not an Effect of mere muscular Motion.
Let it be observed whether the Stroke is sometimes given on the near Approach of a conducting Body without actual Contact; if so, that is another similar Circumstance. Then observe whether in that Case any Snap is heard; and in the Dark whether any Light or Spark is seen between the Fish and the approaching Body.4 If not, there the Fluids differ.
Let a Number of Persons standing on the Ground, join Hands, and let one touch the Fish so as to receive the Stroke. If all feel it, then let him be laid with his Belly on a Plate of Metal; let one of the Persons so joining Hands touch that Plate, while the farthest from the Plate with a Rod of Metal touches the Back of the Fish; and then observe whether the Force of the Stroke seems to be the same to all in the Circuit as it was before, or stronger.5
Repeat the last Experiment with this Variation. Let two of the Persons in the Circuit hold each an uncharg’d electric Phial, the Knobs at the Ends of their Wires touching. After the Stroke, let it be observ’d whether those Wires will attract and repel light Bodies; and whether a Cork Ball suspended by a long silk String so as to hang between the Wires at a small Distance from the Knob of each, will be attracted and repell’d alternately to and from each Knob; if so, the Back and Belly of the Fish are at the Time of the Stroke in different States of Electricity.6
B Franklin
Endorsed: Franklins Instructions to try if the stroke of the Torpedo be Ellectrical.
9. Walsh to BF below, July 1, 1773.
1. See his letter above of July 12, and his fuller report below, Aug. 27.
2. Dubourg, Œuvres, I, 269–71. We note only substantial differences between the draft and the ADS.
3. The draft reads “Fluid, similar in one Property at least, to that of Electricity.”
4. The draft here concludes as follows: “If so, it agrees in more Properties with the Electric Fluid.
“Lastly, Touch him with the Wire of a small electrical Phial, and if the Shock can be receiv’d thro’ it, observe whether the Wire will afterwards attract and repel light Bodies, and give a Stroke when held in one Hand and the Wire touch’d with the other. If so, the Fluid producing these Effects seems to have all the Properties of the electric Fluid.”
5. BF is suggesting the same kinds of experiment as those conducted years earlier with the Leyden jar, for which see Abraham Wolf, A History of Science, Technology, and Philosophy in the Eighteenth Century (2nd ed., revised; 2 vols., New York, 1961), I, 221–3.
6. Dubourg for some reason omitted the final clause. In this paragraph BF is designing another test, which Walsh apparently did not make, of analogy with the Leyden jar; the principle is the same as that of his own experiment described above, III, 158, 160.