Pambour, François Marie Guyonneau De
PAMBOUR, FRANçOIS MARIE GUYONNEAU DE
(b. Noyon, France, 1795)
Pambour attended the École Polytechnique (1813–1815) and upon being commissioned he entered the artillery; later he transferred to the general staff. His principal contributions were to the theory and practice of steam engines and steam locomotives.
His Théorie de la machine à vapeur, which went through several editions and translations, had a fundamental and mathematical approach such as might be expected from an applied physicist rather than a practical engineer. As late as 1876 the work was authoritatively referred to as “the most celebrated treatise of Pambour … published in 1844, then far superior to other works and still in many respects one of the best standards on the subject.” In his definitive treatise, R. H. Thurston frequently refers to Pambour’s work in the highest terms. He points out that much of his original work has been “demonstrated anew by a certain number of modern writers who appear to ignore the works of Pambour.” Pambour was certainly not a mere empiricist. His original researches were reported in papers communicated to Comptes rendus of the Academy of Sciences. In addition to his treatise on the steam engine, he wrote an equally successful practical work, Traité théorique et pratique des machines locomotives (1835).
Despite his productivity, Pambour was never a member of the Academy. A candidate for the Section de Mécanique in 1837, 1840, and 1843, he failed to be elected, quite possibly as a result of scientific differences with Poncelet, Probably intensified by a personal clash. There was a polemic between Pambour and Poncelet’s protégé, Morin, over the choice of “frictional coefficients” for calculating the work of piston expansion. This quantity relates the volumes occupied by a unit weight of steam in the boiler and in the cylinder. According to the older theory of Poncelet and Morin, the ratio can be determined by a constant coefficient. In the new theory of Pambour, the coefficient is no longer constant, but varies with operating conditions. Pambour’s denunciation of Poncelet’s earlier work elicited a sharp response. Not only was Pambour rejected by the Academy, but his name does not appear in the École Polytechnique, Livre du centenaire, which includes biographical sketches of considerably less distinguished graduates.
Pambour’s most important contribution to the theory of the steam engine dealt with the calculation of the work obtained under a given set of operating conditions. An earlier treatment, developed by Poncelet and Morin, calculated the work of expansion by the use of Boyle’s law but did not take into account the drop in steam temperature upon expansion. Pambour, on the other hand, assumed that the steam remained saturated throughout the engine; and since the temperature of saturated steam varies with pressure, Boyle’s law is quite incapable of representing this situation. Instead, Pambour used an empirical formula that involved two experimentally determined constants. He assumed various pressure situations between the boiler and the cylinder and with his formula calculated the work for these cases. The assumption that steam is saturated during expansion is not used today; the Rankine cycle—where the expansion is from superheated steam into wet steam— has replaced Pambour’s scheme. The improvement over the assumption of Boyle’s law was tremendous and represented a major advance. Clapeyron used Pambour’s formula in his 1851 lectures but recognized the shortcomings inherent in the assumption that the steam was “dry.”
There are forty-four papers by Pambour on the steam engine in Comptes rendus hebdomadaires des séances de l’Académie des sciences,4–21 (1837–1845). His subsequent interest in hydraulic turbines was reflected in seventeen papers in vols. 32–75 (1851–1872). Théorie de la machine à vapeur appeared in French (Brussels, 1837; Paris, 1839, 1844; Liège, 1847, 1848), in English (London, 1839; Philadelphia, 1840), and in German, with intro. by A. L. Crelle (Berlin, 1849).
On Pambour’s candidature at the Academy, see Comptes rendus,4 (1837), 556; 10 (1840), 504; and 17 (1843), 1310.
On Pambour and his work, see James Renwick, Treatise on the Steam Engine, 3rd ed. (New York, 1848), pref.; R. S. McCullock, Treatise on the Mechanical Theory of Heat and Its Application to the Steam Engine (New York, 1876), pp. 24, 261–263; R. H. Thurston, Traité de la machine à vapeur, I (Paris, 1893), 260; and F. Zernikow, Die Theorie der Dampfmaschinen (Brunswick, 1857), 14–23.