To Jean Baptiste LeRoy
Paris Apr. 3. 1789.
I return you with many thanks the Volume with D. Bernoulli’s paper which I have read with great satisfaction. I observe that the proposition of M. Bernoulli differs from Mr. Rumsey’s in several essential points. 1. His Water was to be raised by man: Rumsey’s by elastic vapour. 2. Bernoulli’s water was to act on an inclined plane: Rumsey’s on a direct one. 3. Bernoulli’s was to act by it’s specific gravity only: Rumsey’s by a forcing pump. These three differences are important. The 4th. is not so, to wit Bernoulli’s vessel was to be moved by the direct action of the water: Rumsey’s by it’s reaction. I have the honour to be with great and sincere esteem Dear Sir Your most obedt. humble servt.,
The entry in SJL does not make it clear whether this letter is addressed to Julien David LeRoy (1728–1803), architect and writer on navigation and maritime subjects, or to his brother, Jean Baptiste LeRoy (1720–1800), a physician, an experimenter in electricity, and editor of the Journal de physique, both of whom were known to TJ and also to Franklin; it was evidently addressed to the latter, to whom TJ introduced James Rumsey in Mch. 1789 and with whom he was in correspondence concerning Rumsey’s steamboat and other inventions (LeRoy to TJ, 30 Apr. 1789). It was to the former that Franklin sent his famous “Maritime Observations” in the form of a letter—a miscellaneous “nautical budget” that also animadverted upon (and suggested an improvement in) the jet-propelled boat proposed by Daniel Bernoulli (1700–1782), a distinguished mathematician of the well-known Dutch family of scientists and holder of different professorships at Basel, where his father and uncle had preceded him (text of Franklin’s letter, as to a “Mr. Adolphus le Roy,” is in Amer. Philos. Soc., Trans, ii , 294–329, especially p. 308). In 1753 the Académie des Sciences awarded Bernoulli its prize for his treatise “Recherches Sur la maniere la plus avantageuse de suppléer à l’action du Vent sur les grands Vaisseaux, soit en y appliquant les Rames, soit en y employant quelqu’autre moyen que ce puisse être. Fondées Sur une nouvelle Théorie de l’économie des forces et de leurs effets.” This was first published as No.3 in Recueil des pieces qui ont remporté des prix de l’Académie Royale des Sciences, depuis leur fondation. Tome Septieme. Qui contient une partie des pieces de 1751, 1752, 1753, 1759, 1760 et 1761 (Paris, 1769). The Editors are indebted to Mrs. Gertrude D. Hess, Assistant Librarian of the American Philosophical Society, for identifying this as the volume with Bernoulli’s paper that LeRoy had lent to TJ. Bernoulli’s scheme and the method proposed by Rumsey (see note to LeRoy to TJ, 30 Apr. 1789) have been compared by scholars (e.g., A. Wolf, History of Science, Technology, and Philosophy in the Eighteenth Century, p. 570), but never more succinctly than in the present letter. TJ owned a copy of Bernoulli’s Hydrodynamica, Basel, 1738 (Sowerby, description begins E. Millicent Sowerby, comp., Catalogue of the Library of Thomas Jefferson, 1952–1955, 4 vols. description ends No. 3742).