To Benjamin Franklin from Julien-David Le Roy, [10–11 April 1784]
From Julien-David Le Roy
L:1 American Philosophical Society
This is the first known letter to Franklin from Julien-David Le Roy, one of the three brothers of Franklin’s close friend and neighbor Jean-Baptiste. Franklin had met the brothers during his first visit to Paris in 1767.2 Julien-David, though best known as an architect, was also an expert on ancient ship design and navigation. He had begun studying lateen (triangular) sails in the 1760s, and presented his first paper on the subject in 1770.3 In 1782, he conducted a series of experiments designed to prove the advantages of using ancient sail designs on modern vessels. On September 24 of that year, with Franklin as a witness, he sailed a small boat rigged with lateens down the Seine from Paris and performed dexterous maneuvers in front of the Hotel de Valentinois. Julien-David described those trials in a work published at the end of 1783, Les Navires des anciens, in which he paid homage to Franklin as “le pere de tant de découvertes.”4
Franklin began a written response to what he called Le Roy’s “learned Writings on the Navigation of the Antients” in February, 1784, proposing to offer his own thoughts on sail design. Before having completed those thoughts, however, he put the letter down, and only resumed it during his voyage to Philadelphia in August, 1785. As the weeks wore on and more ideas occurred to him, Franklin expanded his letter to Le Roy into the paper now commonly known as “Maritime Observations,” which he submitted to the American Philosophical Society upon his arrival.5
Les Navires des anciens contained an appendix in which Le Roy wrote a series of speculations on how balloons could be useful in a maritime context: to save shipwrecked sailors, to improve naval maps, to explore ocean currents, and even to function as sails.6 In the spring of 1784 he wrote a memoir that expanded on those ideas, attempting in part to lend his expertise to the problem of how to steer balloons. He sent that memoir to Franklin under cover of the present letter.
[April 10–11, 1784]7
Monsieur,
Vos profondes connoissances dans la Physique et dans les Arts, le génie également Simple et Sublime qui vous en a fait tirer des résultats si utiles et si nouveaux, et l’intérêt que vous prenez à mes recherches sur la Marine; m’enhardissent à vous Soumettre quelques idées que j’ai eues sur les moyens de diriger l’Aérostat.8
Ces moyens different essentiellement les uns des autres. Je n’aurai l’honneur, Monsieur, de vous en proposer qu’un petit nombre, parceque, d’après vos principes, j’ai rejetté tous ceux qui se présentant à mon esprit, ne m’ont pas paru marqués au caractere de Simplicité qu’on observe dans les inventions les plus utiles aux hommes./.9
Addressed: A Monsieur Frankclin, / Ambassadeur et Ministre plénipotentiaire / des Etats Unis de L’Amerique.
1. The letter and the enclosed memoir are in a secretarial hand. Le Roy made minor changes to the text of the memoir, and at the bottom of its final page added the date “11 avril 1784.” At the end of the summer Le Roy submitted to BF a second memoir (described below); it is in the hand of the same secretary who wrote the first memoir, with the exception of the final five pages, which were written by Le Roy. We are indebted to Abigail E. Shelton of the APS for identifying Le Roy’s handwriting and to Prof. Christopher Drew Armstrong for confirming it.
2. XV, 82–3; XXIX, 634n.
3. Christopher Drew Armstrong, Julien-David Leroy and the Making of Architectural History (London and New York, 2012), pp. 242–5, 254n; Le Roy, “Premier memoire sur la marine des anciens,” Histoire de l’Académie royale des inscriptions et belles-lettres for 1770–72, XXXVIII (1777), 542–97. BF’s copy of the latter is at the APS.
4. Julien-David Le Roy, Les Navires des anciens, considéréspar rapport à leurs voiles, et à l’usage qu’on en pourroit faire dans notre marine (Paris, 1783), pp. 87–91. The experiment was witnessed by at least one other member of BF’s circle, [Philip?] Keay (XXV, 725n), whom the author considered knowledgeable about naval matters: Julien-David Le Roy, Nouvelles recherches sur le vaisseau long des anciens … (Paris, 1786), p. 29; Julien-David Le Roy to BF, June 20, 1786 (APS). We have no record of when Le Roy gave BF a copy of Navires des anciens, but suspect it was in mid-December, around the same time that he sent a copy to the Royal Society of London: Phil. Trans., LXXIV (1784), 503. BF’s copy is now at the APS.
5. BF’s draft of “Maritime Observations” is at the Library of Congress. His initial dateline read “Passy, Feb. [blank] 1784”. After finishing the MS he added lines above and below that dateline in a different ink: “Began at” / “but finished at Sea. Aug. 1785”. Because the bulk of the paper was written in August, 1785, we will publish it under that date.
6. “Observations Sur la Machine Aërostatique, relatives à la Marine & à la Géographie,” in Navires des anciens, pp. 225–39.
7. Although Le Roy added the date of April 11 at the bottom of his first memoir, as noted above, the second memoir is entitled a continuation of the letter written on April 10, 1784.
8. The enclosure, “Différentes idées Sur la maniere de diriger l’Aérostat,” is 17 pages and divided into four sections. In the first section, Le Roy addresses the urgent problem of how to protect balloonists in case of crash landings on land and in water. He suggests giving balloons the shape of a cone to increase air resistance during an unplanned descent. He also recommends making the gondola detachable, so that it can serve as a boat when landing on water. In the following sections, he offers on three methods of steering balloons: with a harnessed flock of trained birds, a fan-like paddle, and a set of windmill blades. These proposals are illustrated in two professionally drawn plates, the first of which is shown on the facing page. (For more information, see the List of Illustrations.)
9. Sometime after Aug. 12, Le Roy submitted to BF what he called a continuation of his earlier memoir, entitled “Sur divers moyen de diriger Les Aerostats” (27 pp. including one plate of professionally drawn illustrations and a crude pencil sketch of an unidentified apparatus). It was written in two stages. The first part, in the hand of Le Roy’s secretary, concerns the near-disastrous balloon experiment by the Robert brothers and Meusnier at Saint-Cloud on July 15 (for which see the July 15 entry in BF’s journal, [June 26–July 27]). Le Roy criticizes the oblong shape of the balloon and its all but useless paddles and rudder. Still concerned about balloonists’ safety during falls, he dismisses parachutes designed by Blanchard as ineffective and instead proposes encasing the lower half of the globe in a frame resembling an inverted umbrella. As an alternative to a rudder at the tail of the gondola, Le Roy would install a windmill propeller. Rather than an oblong shape, he proposes a cylinder with cones tapering to a point at either end, or else two cones attached at their circular bases. In a final section, handwritten by Le Roy, he recounts a discussion he had on Aug. 12 with a physicist (identified in the margin as “Mr. Testu”) and imagines an improved method of managing atmospheric pressure during flight.
At some point Le Roy had his secretary make a fair copy of a revised version of the memoirs, cover letters, and plates. Beneath the title of the first memoir, which begins with a variant of the cover letter published here, Le Roy added the date “du 10 Avril 1784”. Beneath the title of the second memoir, he added “du 5 Septembre”. We do not know for whom the packet was intended; the MS is now at the National Library of Scotland. Le Roy deleted from the first memoir the section about harnessing trained birds, and they are likewise omitted from the illustrations. In a postscript, he admitted that the method was too complicated. Le Roy also added a footnote to the section on windmill blades stating that subsequent to writing the original memoir, he learned from BF about previous uses of windmill blades to move bodies on water. To the second memoir, Le Roy added three final paragraphs that relate to the illustrations.
Julien-David Le Roy’s Designs for Improving Hot-Air Balloons