PITOT, HENRI

(b. Aramon, Languedoc, France, 3 May 1695; d. Aramon, 27 December 1771)hydraulics.

Pitot was the son of Antoine and Jeanne Julien Pitot. He was born into a patrician family of Aramon, a small town between Avignon and Nîmes. His scholarly career began inauspiciously. In his youth he felt such extreme repugnance against any form of study that his parents, in despair, let him begin a military career, which lasted only briefly. His chance discovery of a geometry text in a Grenoble bookstore led him to return home and spend some three years studding mathematics and astronomy.

In September 1718 Pitot set out for Paris. He was introduced to Réaumur, and won his goodwill. Réaumur advised him on his further studies and let him use his library, and through him Pitot began, at first informally, the association with the Académie de Sciences that was to last more than twenty years. In 1723 Pitot became Réaumur’s assistant in the chemical laboratory of the Academy, a position that Pitot filled without neglecting his original interest in geometry. He was promoted adjoint mécanicien in 1724 and in 1733 became pensionnaire géomètre. In 1740 Pitot accepted an invitation from the Estates General of Languedoc to supervise the draining of swamps in the lower parts of the province. After the successful completion of that task, he became director of public works of one of the three districts of the province and superintendent of the Canal du Languedoc (now Canal du Midi). He lived in Montpellier until his retirement in 1756, when he returned to Aramon. In 1738 he married Marie-Léonine de Saballoua; their only surviving child, a son, was later attorney general in Montpellier.

Pitot’s scientific career was both theoretical and practical. During his two decades at the Paris Academy he published a variety of papers dealing with astronomy, geometry, and mechanics, especially hydraulics. The papers offered competent solutions to minor problems, arrived at by elementary mathematics, and without lasting significance. From 1740 to 1756, he was active as a civil engineer. At least two significant engineering projects of his survive—the road bridge attached to the first level of the Pont du Gard, the famous Roman aqueduct near Nîmes, and the aqueduct that supplies drinking water to the city of Montpellier.

Pitot’s only book, La théorie de la manoeuvre des vaisseaux (Paris, 1731), dealt with a subject of much contemporary interest (books on it had been published in 1689 by Bernard Renau, in 1714 by Johann I Bernoulli, and in 1749 by Leonhard Euler), and was well received; it was translated into English and earned him membership in the Royal Society of London.

Pitot is also remembered for his invention of a simple instrument for measuring the velocity of flowing fluids and of moving ships, which he reported in “Description d’une machine pour mesurer la vitesse des eaux courantes, et le sillage des vaisseaux,” in Mémories de l’Académie royale des sciences, 34 (1735), 363–373. The device consisted in principle of a simple glass tube, the end of which was bent at right angles. It was inserted into a river in such a way that the opening faced upstream. Since the water level in the tube rose considerably above that of the river, Pitot reasoned that the difference at the level was equal to the height from which water had to fall to acquire the velocity prevailing at the location of the tube’s opening. In other words, the device permitted the determination of the local velocity of fluids directly; that is, without clock and yardstick, and even at locations deep below the surface. The instrument was quickly accepted, and it has remained, under the name “Pitot tube,” one of the basic experimental tools of fluid dynamics.

BIBLIOGRAPHY

I. Original Works. Apart from La théorie de la manoeuvre des vaisseaux (Paris, 1731), Pitot published (virtually all in the Histoire et mémoires de l’Academie royale des sciences) a considerable number of papers that are listed in Poggendorff, II (1863), 459.

II. Secondary Literature. The basic source to all later biographical efforts is Grandjean de Fouchy, “Éloge de M. Pitot”, in Histoire de l’Académie royale des sciences, 73 (Paris, 1774), 143–157. Discussions of Pitot’s contributions to mathematics and hydraulics are Pierre Humbert, “L’oeuvre mathématique d’Henri Pitot”, in Revue d’histoire des scienes et de leurs applilcations,6 (1953), 322–328; and René Chevray, “A Man of Hydraulics: Henri de Pitot (1695–1771),” in Journal of the Hydraulics Division, American Society of Civil Engineers, 95 (1969), 1129–1138.

Otto Mayr