To Jacques Barbeu-Dubourg
ALS (incomplete draft): American Philosophical Society; incomplete translated extract: printed in Jacques Barbeu-Dubourg, ed., Œuvres de M. Franklin … (2 vols., Paris, 1773), 1, 321.
London, May 28 [-June 1]. 1773
I have received your Favour of the 13th Instant with several Packets of the Sheets. I have examined more of them, and hope to finish examining the rest before next Post, when I shall send you what Remarks have occur’d to me, towards furnishing your Errata.5
I much like the Letters you propose to insert, as written from you to me; and am oblig’d to you for them, as they will adorn my Work. An Answer to one of them went in Tuesday’s Packet; but I am afraid ’tis written with too serious an Air. Mould it as you please.6 Some Observations on the others may soon follow. At present I confine myself, to what you seem most desirous of having immediately, my Remarks on the Translation of the Papers relating to the Powder Magazines.7 The Difficulty lies in the technical Terms used by Builders. To explain these, I must try to make a little Sketch of one of the Magazines.
aa is what in my Papers is called the Ridge of the House, and what appears you would call in French Sommet, ou faîte, and not corniche, as that would go along under the Eaves, as at bb.
The Shaded part from a to a, represents the bent Plate of Lead 22 Inches wide which covers the Ridge, from End to End, 11 Inches on each side, to prevent the Entrance of Rain where the Slates meet at top. This Plate of Lead, which in English we call a Coping, I suppose you would call Plaque or chaperon perhaps and not entablement. c is the Wall. d the Conductor [in margin: extending above the Ridge, but well united with the Plate of Lead at a].
Thus I imagine you would say at the Beginning of Section 2d of the Letter to Major Dawson, (but in better French than mine) “Que le batiment qui a une plaque [ou chaperon] de plomb le long du Sommet [ou faîte] peut etre garanti, &c. communiquant avec cette plaque [ou chaperon]” &c.8 And at the End of the same Section; instead of le plomb qui couvre la corniche, say, la plaque du plomb qui couvre le sommet du comble. In the 3d Section, where mention is made of corniches revetues de plomb, perhaps it may be right instead of corniches to say, faîtes, ou sommets. And near the End, instead of entablements to say plaques, and instead of corniche, to say faîte, ou sommet. But as I am not Sure that I understand your Term arcboutans, I have endeavoured to give you the Form of these 4 Roofs, by a Sketch, wherein ab is the Ridge covered with Lead; ca and da are what we call the Hip-Joints, or Joinings of the Sloping Roof of the End with the sloping Roof of the Sides, which Joinings are also covered with Lead, to prevent the Entrance of Rain where the Slates meet. In this Form of Roof, the Proposal is, that the Iron Conductor should rise from the Wall e, as high as f, and thence extend its Arms to c and d. Thus the pointed Rod being erected at a would communicate with the Iron Conductor by means of the leaden Coping on the Hip Joints ac and ad.
In the Note after the Letter to Major Dawson, I would omit the Words à faire le frais du reste. The Idea of the Board being only this that they should be better justified in the Public Opinion, if they obtain’d the Sentiment of the Royal Society in favour of the Project, than if they acted upon the Advice of a single Person. As to the Expence, it was entirely in their own Power.
In the Report of the Committee near the Beginning of the second Paragraph for entablement de plomb, I suppose it should be plaque de plomb; and in the same line, for corniche, say faîte, or sommet du comble. Again in the 4th Paragraph, for entablement de plomb le long des goûtiêres, perhaps it might be, plaques de plomb le long les jointures du toit, jusques les goutieres, qui sont aussi de plomb, d’ou descendent, &c. I see my French must be abominable, but I hope you will understand it better than my English. Near the End of the 7th Paragraph, for corniche read sommet twice. In the 8th Parag. for grosseur read roideur, for corniche read sommet, and perhaps for l’entablement, read plaque; but I begin to think I do not rightly comprehend the meaning of your Word entablement; and that it may be proper in this Place. Towards the End of the 9th Paragraph for étendûë sur le comble, &c. read, étendûë sur le toit, [or, au travers du toit] avec la plaque de plomb du sommet, cette plaque de plomb étant absolument semblable a celle du sommet. In Paragraph 10. for corniche, read faîte, twice. All the rest seems to be right.
I suppose you have Copies of the Translations, you sent me, and that therefore I need not return them, as they would swell the Packet. I am, ever, with Love to Mrs. Dubourg, Your affectionate humble Servant
P.S. June 1. [I] wish with you, that some Chymist, (if he is at the same time an Electrician, so much the better) would, from the excellent Hints in your Letter,9 work on Glass with your Views. With a thorough Knowledge of that Substance as to its electric Qualities, we might go to work with greater Certainty in making our own Experiments, and in repeating those made by others in different Countries; which latter have I think, often succeeded differently, by the Use of different kinds of Glass, and thereby occasioned Misunderstandings and a Contrariety of Sentiments.
There is another Desideratum in Glass, that it should not be liable to break through when highly charg’d in the Leiden Experiment. In 20 Bottles discharg’d together I have known 8 so destroy’d, in 35, 12. The Loss on these Occasions is very discouraging to Electricians that would accumulate a large Force, necessary for some Experiments. What the Cause is, of this Rupture, has not yet been explained.1 The first Thought naturally is, that the Positive Electricity accumulated on one Side of the Glass, bursts through to supply the Deficiency on the other and restore the Equilibrium. But I conceive this cannot be the Case, when I consider, that where a Number of Bottles are so united that they may be charg’d and discharg’d together, the Bursting of one alone would discharge the whole Number; and therefore, that if it depended on some Weakness in the Glass, it is not probable that 8 should have precisely the same degree of Weakness, so as all to break at the same Instant, but that the weakest would break first and thereby secure the rest. That when a certain Effect is to be produced, by the whole Quantity passing in the destin’d Circuit, as the Melting of a Wire for Instance, if the Charge instead of passing in the Circuit should burst thro’ the Sides of the Bottles the intended Effect must fail, which however does not happen. For these Reasons, I suspect that there is in the Substance of the Glass either some little Air Bubble, or some Particle of unvitrified Sand or Salt, into which a Quantity of the Electric Fluid may be forced during the Charge, and there confin’d, till the general Discharge, when the Force being suddenly taken off, its elasticity acts on the confining Glass from which it cannot so soon escape and therefore bursts it. This I offer only as a Conjecture for others to examine.
The Globe I had which could not be excited, tho’ from the same Glass house with others that were excellent, was not out of the same Pot.2 The common Glass made there was a little Greenish, and work’d up chiefly for Windows and Bottles. But the Workmen once attempted to make a Pot of White Glass, and the above-mentioned Globe was out of that Pot. The Glass prov’d not of a clear white, was therefore not lik’d, and therefore they gave over that Attempt. I suspected that there was too much Salt in the Composition; but I am ignorant of those matters.
Your Para Tonnerre is ingeniously contrivd.3 And tho’ the Chance is small that any one Person walking abroad shall be struck by Lightning, yet as it sometimes happens, and some may think the Chance, small as it is, worth guarding against, I know not how they can do better than use your Contrivance. Perhaps [remainder missing.]4
5. The promised letter was presumably either the missing one of June 22 or that of the 29th below.
6. See above, under May 25. Dubourg clearly refrained from “moulding” the letter.
7. The letter to Dawson and the report of the Royal Society’s committee on the Purfleet magazine (above, XIX, 154–6, 262–5) were printed in Dubourg, Œuvres, 1, 280–7.
8. Dubourg had written (p. 280) “que le batiment qui a un entablement de plomb le long de la corniche … peut etre garanti … communiquant avec cet entablement …” In his errata he changed entablement to chaperon and corniche to faitière. The suggestions that follow he embodied in the text, improving on BF’s French in the process. Brackets in this paragraph are in the original draft.
9. Of March 25 above.
1. See above, XVIII, 181.
2. See above, V, 521.
3. It is described in Dubourg’s letter above, April 1.
4. The printed extract, which begins with this paragraph, gives more of the sentence but breaks off in the middle of it: “Peut-être pourriez-vous simplifier encore votre instrument, et vous contenter de faire adapter à un parasol ordinaire vos. …” Dubourg here appended the following note:
“J’ai fait en conséquence, non-seulement au Paratonnerre, mais encore à la lettre qui l’annonçoit, un petit changement dont l’objet n’est pas assez intéressant pour en rendre compte ici plus au long; mais j’ai cru devoir persister à mettre tout ce qu’il y a de métallique en-dessus, pour tranquilliser d’autant plus les esprits prévenus de terreurs paniques, qu’on ne peut pas déraciner en un jour.
“J’ai fait faire ce Paratonnerre, par un de mes voisins, qui l’a tres-bien exécuté à mon gré. (Le Sieur Bairin de la Croix, Ingénieur du Cabinet de Physique et d’Optique du Roi, demeurant rue Copeau, à Paris).”