Benjamin Franklin Papers

To Benjamin Franklin from Jan Ingenhousz, 3 May 1780

From Jan Ingenhousz

ALS: Library of Congress

Brussels May 3. 1780

Dear friend,

I hope you are not so entirely involved in the troublesome business of the world Politic, as to have abandon’d entirely the world of Nature, whose laws, made by the supreme wisdom are as constant, and inalterable as its Legislator himself. It would, indeed, be hard to me to concieve, that a man, a Philosopher so often and so successfully employed in researches of the most intricate and the most mysterious operations of Nature, should have so far lost all feelings for those truly delightfull occupations of mind, as to be given over without reserve to the pursuit of systemes framed by men, and build upon foundations of so little solidity, as to be often overturned by mere changes and accidental circumstances.

I have so much the more reason to be persuaded that you are not lost to the world of Nature, tho many of your old friends thinck so, as I know by repeated experience, how3 easy it is to induce you to the contemplation of nature, by reasoning upon philosophical subjects. Your reading with so much eagerness the result of my philosophical inquiries, your constant readiness to listen to the news of any discovery in natural knowledge and to give your opinion on questions which I proposed to you so often, when I had the pleasure of enjoying your company last winter,4 encourage me to submit to your consideration some difficulties on Electricity, which some eminent philosophers thinck inexplicable by your allmost universaly recieved systems of positive and negative electricity.

I. If the electrical fluid is truely accumulated on the inside of a Lyden phial and expelled in the same proportion from the outside, why are the particles of glas not all thrown outwards, when the phial, being overcharged, breaks or is perforated by a spontaneous explosion?

II. When a strong explosion is directed thro a pack of cards or a book, having a piece of tin foil between several of its leaves, the electrical flash makes an impression on some of those metallic leaves, by which it seems as if the direction of the electric explosion had gone from the outside towards the inside, when on the other metallic leaves the impression is in such a direction, that it indicates the current of electrical fire to have made its way from the inside of the phial towards the outside: so that it appears to some electricians, that in the time of the explosion of an electrical phial, two streams of electrical fire rush at the same time from both surfaces and meet or cross one another.

III. When a flash of lightning happens to hitt a flat piece of metal, the metal has sometimes bien pierced by several holes, whose edges were turn’d some the one way, and some the other. So that it has appeared to some philosophers that several streams of electrical fire had rush’d in one way and some the opposit way. Such an effect of lightning has been publish’d lately by father Barletti.5

IV. Tho from the very charging of the Lyden Phial, it seems clear, that electrical fluid does in reality not pervade the substance of glas; yet it is still difficult to concieve, how6 such a subtil fluid may be forced out from one side of a very thick pane of glass by a similar quantity of electrical fire trown upon the other surface, and yet that it does not pass thro any substance of glass, however thin, without breaking it. Is there some other fact or illustration, besides those to be found in your public writings, by which it may be made more obvious to our understanding, that electrical fire either does not enter at all the very substance of glas and yet may force from the opposit surface an equal quantity; or that it enters realy the pores of the glas on the positive side, and yet that it can not pervade the thinnest lamella of glas without breaking it? Is there any comparative illustration or exemple in nature, by which it may be made clear, that a fluid throw’n upon one surface of any body may force out the same fluid from the other surface without passing thro this substance?

I should wish to be informed, how you account for these phenomena, and to recieve you answer upon one or other when you have made up your mind about it, without waiting for the solution of the rest.

If you could communicate to me some short hints, which may occur to you about the most convenient manner of constructing gun powder magazines, the manner of preserving the powder from moisture and securing the building in the best manner from the effects of lightning, you would oblige me. Whatever may occur to you on this head, will be very acceptable. It seems to me very imprudent to heap up immense stores of that terrifying ingredient in stony vaulted buildings in the time of piece, when there is no danger of any combustible matter being thrown upon it, and more so to place several of such storehouses so near one an other as may endanger them from being all blown up, when one should happen to be set on fire by what ever accident it may be. Mr. Le Roy did not keep his word in showing me your advise upon this.

You know, that his Imperial Majesty has intrusted me with the direction of such repositories for as far as regards the danger from lighning. Since this important trust was put upon me, I have thought it my duty to consider this matter with more attention as I used to do before. I have allready a good provision of reflexions, which I intend to lay before the public, as soon as I shall find my self disposed to the undertaking of putting them in good order.

Permitt me to trespass a little more on your time, and to beg you to lay aside, for a few hours, the heavy wight of public affaires, your country has entrusted you with, to fulfill your intended sceem to determine by a well adapted experiment, what metals are the best and readyest conductors of heat. You have allready entrusted me with the account of the method you imagined as decisive for the determination of this point. But, having no right to make any use of this knowledge I am impatient to be informed of its success.7

As you never refused me some hours of philosophical conversation, whenever I have the pleasure of being with you; I may with as much confidence sollicit you to bestow now and than an hour in answering by writing to some philosophical questions, and thus steal from your political occupations consecrated only to the service of your own country, some hours for the benefit of whole mankind. I can commit no indiscretion in endeavouring to prevent, that such of your philosophical notions, as never are or never would have be known to others, may not be lost to the world. Your ennemies even, I trust, would not grudge at my corresponding with you on such subjects, tho in the middel of that political convulsion, which continues still to shake the very foundations of the mightyest empire, which ever existed on the surface of the earth, and which embitters the minds of many against those, who happened to have a great share in this awfull revolution of human affaires.

Lettres directed to my name au soins de mr. devroom marchand sur le marché au beur(?) a Bruxelles, will come to right.

One of the best and most skillfull electricians I ever saw, is a young gentleman here, 19 years old, the son of a rich banker, whose name is Walkiers. He does scarce meddle with any thing but Electricity, and his father encourages this particular taste. His electrical machine far excells every one I ever saw, his battery is the strongest, that I ever met with. He has a genius for contriving new experiments, and understands thoroughly the theory. He has a most sensible conductor upon the house, which is affected very often by distant clouds or even without clouds. I expect great thinks from him, the more so, as I am [torn: one word illegible] natural knowledge can make but slow progress in the hand of those, who doe not pursue one single object with ardour, and leave allmost every other object aside.8

I made some experiments with this young gentleman on purpose to discovre the law, by which are produced the direction of the burrs upon cards and of the impressions and holes in leaves of tin foil, laid between cards, when a strong blast of an electrical explosion is directed thro them. I observed that those burrs and impressions had no regular direction, when the pack of cards was equaly pressed on bothe sides between the two nobs of metal which serve [to] convey the electrical explosion thro them. The stream was allso allways divided in different branches by passing thro these cards and pieces of tin foil, as on some there appeared two three or even more burrs and impressions, which had a contrary direction even on the same piece. Mr. Walkiers had allready made very accurate observations on this head, and found constantely that the direction of these burrs and impressions is allways towards that side where was the least pression. He produced realy these burrs and impressions on what ever side he pleased. This seems to demonstrate, that they produced by the explosion of the body happening at the moment this rapid fire makes its way thro it, the parts of the body taking the direction towards the weakest resistance.

I am with great esteeme Dear frend Your most obedient humble servant and faithfull frend

J. IngenHousz

Endorsed: Dr. Ingenhauss Philosophy

[Note numbering follows the Franklin Papers source.]

3Ingenhousz wrote “who”. BF underlined the word and corrected it.

4For Ingenhousz’s visit to Paris, and BF’s interest in his recent work, see XXXI, 121–4, 140n, 360. We do not know for how many months Ingenhousz stayed, nor whether he accepted BF’s offer of lodging, but the two men spent a considerable amount of time together. In addition to discussing electricity and the conductivity of metals, mentioned in this letter, they evidently also spoke about BF’s idea for a new stove (Ingenhousz to BF, Oct. 2, 1782, APS; XX, xvii–xviii, 251; XXVII, 506–7), and his theories on the causes and cure of smoky chimneys (which he finally wrote at Ingenhousz’s urging: Smyth, Writings, IX, 317, 413–43). At some time during 1780, perhaps inspired by a conversation at Passy, Ingenhousz invented his “new” electrical machine: inexpensive, portable, and constructed primarily of unbreakable parts. Ingenhousz, Nouvelles expériences et observations sur divers objets de physique (Paris, 1785), pp. 99–116, pl. I; W.D. Hackmann, Electricity from Glass: the History of the Frictional Electrical Machine 1600–1850 (Alphen aan den Rijn, Netherlands, 1978), p. 140.

5Carlo Barletti, Analisi d’un nuovo fenomeno del fulmine ed osservazioni sopra gli usi medici della elettricità (Pavia, 1780). Barletti, whose conclusions were anti-Franklinist, analyzed the phenomenon of how a recent lightning bolt had perforated the weather vane on a Cremonese church. Ingenhousz had reviewed the work with BF during his visit at Passy (Ingenhousz to BF, Aug. 20, 1782, APS). See Antonio Pace, Benjamin Franklin and Italy (Philadelphia, 1958), pp. 31–4; and for the scientific issues, J.L. Heilbrun, Elements of Early Modern Physics (Berkeley, Los Angeles, and London, 1982), pp. 213–18.

6Corrected by BF from “who”.

7Back in Vienna several months later, Ingenhousz did perform this wellknown experiment that now bears his name, although when he published the results he explained that it had been BF’s idea entirely, and all the credit belonged to “ce grand homme.” In early 1780, he wrote, BF had shown him all the preparations; he admired the experiment, and BF generously suggested that they perform it together. To Ingenhousz’s disappointment, BF’s “occupations continuelles” prevented their carrying it out. When Ingenhousz left Paris for Vienna, in July (he must have returned to France after writing the present letter), BF gave him all the equipment, telling him to perform the experiment at his leisure. See “Sur la différence de la célérité avec laquelle la Chaleur passe à travers les différens Métaux,” published in Nouvelles expériences et observations …, pp. 385–6. Ingenhousz finished the experiment around Dec. 5, 1780, when he reported the results to BF (APS).

8Charles-Louis Walckiers de St. Amand (1760–1787) distinguished himself four years later by inventing a large and powerful endless-band electrical machine that was tested by the Académie royale des sciences to its satisfaction. He presented his memoir to the Académie on Jan. 31, 1784, and BF was appointed to the committee that investigated it: Procés-verbaux, tome CIII, fol. 3. See also Hackmann, Electricity from Glass …, p. 140.

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