Du Buat, Pierre-Louis-Georges

(b. Tortizambert, Normandy, France, 23 April 1734; d. Vieux-Condé, Flanders [now part of Nord, France], 17 October 1809)

hydraulics.

Born in the manor of Buttenval, the second son of a minor nobleman, Du Buat was in all probability educated at Paris, where he became a military engineer at the age of seventeen. By 1787 he had risen to the rank of colonel, which he then resigned to accept appointment as lieutenant du roi. His earliest assignments were canal, coastal, harbor, and fortification works in the north of France.

In 1758 Du Buat married a native of Condé (near Valenciennes, on the Belgian border), by whom he eventually had eleven children. On the death of his older brother in 1787, he inherited their late father’s title of count; but with the advent of the Revolution he lost titles and properties and was forced in 1793 to flee with his family to Belgium, then Holland, and finally Germany. In 1802 he returned to Vieux-Condé, and a portion of his estate was restored to him.

Du Buat began his hydraulic studies in 1776, and by 1779 he had published the first edition of his major work, Principes d’hydraulique, copies of which are now quite rare. This was enlarged in 1786 to two volumes, the first of which was analytical and the second experimental; it is supposed to have been translated into English (no copy can be found) as well as German. A posthumous edition of three volumes appeared in 1816, the third volume (Pyrodynamique) having been written during his exile. All three editions carried essentially the same prefatory remarks reviewing the state of the art—in particular those many important topics about which little or nothing was known; portions of the discourse are often quoted in subsequent works because of their continued relevance.

The analytical part of Du Buat’s writings was perhaps more effective than that of such contemporaries as Jean Charles Borda and Charles Bossut, for he dealt extensively with matters of boundary resistance, velocity distribution, underflow, overflow, and backwater. It was in experimental work that he excelled. The results of his 200 separate tests on flow in pipes, artificial channels, and natural streams were to be used by engineers for generations. Even more original was his treatment of immersed bodies. He showed that tests in air and in water could be correlated in terms of the relative density of the resisting medium, and calculated, for example, the size of a parachute required to break the fall of a man of a given weight. He was also the first to demonstrate that the shape of the rear of a body is as important in controlling its resistance as is that of the front.

Du Buat also made 100 measurements on the distribution of pressure around bodies and sought through his findings to develop a new form of Henri Pitot’s “machine” for the measurement of velocity. The basis for his conclusion that the force exerted upon a stationary body by running water is greater than that required to move the same body at the same relative speed through still water (Du Buat’s paradox) is not clear from his writings—i.e., whether the cause is the uneven velocity distribution or the turbulence of the flow. Du Buat is called by some the father of French hydraulics, although at least partial credit should go to several of his contemporaries—not to mention Edmé Mariotte, more than a century his senior.

BIBLIOGRAPHY

Du Buat’s major work was Principes d’hydraulique. ouvrage... (Paris, 1779); 2nd ed. entitled Principes d’hydraulique vérifiés..., 2 vols. (Paris, 1786); 3rd ed. entitled Principes d’hydraulique et de pyrodynamique, 3 vols. (Paris, 1816).

On Du Buat and his work, see H. Rouse and S. Ince, History of Hydraulics (New York, 1963), pp. 129–134; and B. de Saint-Venant, “Notice sur la vie et les ouvrages de Pierre-Louis-Georges, comte du Buat,” in Mémoires de la Société impériale des sciences de Lille, 3rd ser., 2 (1865), 609–692.

Hunter Rouse