(b. Lille, France, 16 September 1876; d. Paris, France, 22 February 1969)
Béghin studied at the École Normale Supérieure from 1894 to 1897 and placed first in the mathematics agrégation in 1897. For over twenty years he lived in Brest, where his inclination toward mechanics was strengthened. At the lycée there he gave courses that would prepare students for the École Navale (1899-1908) and later taught mechanics at the École Navale itself (1908-1921). Béghin organized the training of radio electricians during World War I. He began his university career in Montpellier (1921–1924) and later occupied the chair of mechanics at Lille (1924–1929). He lectured in fluid mechanics at Paris from 1929 to 1932 and was made professor of physical and experimental mechanics and director of the mechanics laboratory. Béghin also taught at the École des Beaux-Arts (1924–1930), the École Supérieure d’Aéronautique (1930-1939), and the École Polytechnique (from 1936). He was elected to the Académie des Sciences on 25 February 1946.
A remarkable teacher and inspirer of applied research, Béghin had a long and fruitful career. His accomplishments stem from his ability to rephrase classical mechanics and to enlarge its scope. Béghin is associated with the most general treatment of systems of nonholonomic linkage, through which he demonstrated, in his first works (1902-1903), how to use Lagrange’s equations in percussion problems. He also provided an elegant extension of Carnot’s theorem that leads to an exhaustive formulation. He extended the solution of Painlevé’s paradox by increasing the examples of dynamic interference due to friction. Béghin also showed the significance of indeterminates, which sometimesappear in very simple cases, for theoretical solutions in a branch of mechanics whose principles do not involve any consideration of microscopic deformations. In elastic impact, he showed that the main characteristic of the end of the impact is that the loss of kinetic energy equals the work absorbed by friction during the impact, and that the reversal of the normal component of the relative speed, until then believed to occur in all such impacts, is realized only under specific conditions of symmetry.
The theory of the gyrostatic compass, which Béghin published in 1921 and later perfected, is significant for his fusion of the extensions of rational mechanics with technical and experimental data. He thus became a specialist in servomechanisms. In this field he studied and experimented with the elimination of vibrations and developed numerous applications, notably for automatic piloting of ships and planes.
Béghin, whose training was classical, was ahead of his time because of his new method of scientific work. He always worked with others, which at times makes it difficult to asses his contribution.
Among Béghin’s writings are “Sur les percussions dans les systèmes non holonomes,”s in Journal de mathématiques pures et appliquées, 9 (1903), 21-26, written with T. Rousseau; “Extension du théorème de Carnot au cas ou certaines liaisons dépendent du temps,” ibid.; Étude théorique des compas gyrostatiques Anschütz et Sperry (Paris, 1921); Statique et dynamique, 2 vols. (Paris, 1921; 7th ed., 1957); “Sur un nouveau compas gyrostatique,” in Comptes rendus de l’Académie des sciences, 176 (1923), written with P. Monfraix; “Étude d’une machine locomotive à l’aide du théorème des travaux virtuels,” in Bulletin de l’élève ingénieur (1924); “Étude théorique d’un compas zénithal gyrostatique à amortisseur tournant,” in Annales hydrographiques(1924), written with P. Monfraix; “Sur certains problèmes de frottement.” in Nouvelles annales de mathématiques, 2 (1924)and 3 (1925); “Sur les transmissions par adhérence,” in Bulletin de l’lévelève ingéniur (1925); Leçons sur la mécanique des fils (Tourcoing, 1927–1929), a course given at the École Technique Supérieure de Textile; “Sur les conditions d’application des équations de Lagrange à un système non holonome,” in Bulletin de la Société mathématique de France, no. 57 (1929); “Sur le choc de deux solides en tenant compte du frottement,” ibid.; Exercices de mécanique, 2 vols. (Paris, 1930; 2nd ed., 1946, 1951). written with G. Julia; Cours de mécanique de l’École polytechnique, privately mimeographed (1942–1943), Vol. I later pub. (Paris, 1947); Cours de mécaniyue théorique et appliquée à l’usage des ingénieurs et des étudiants de facultés, 2 vols. (Paris, 1952); and “Les preuves de la rotation de la terrs,” in Conférences du Palais de la Découverte, ser. A, no. 207 (23 Apr. 1955).
A more complete bibliography and a lengthy list of studies and theses done under Béghin’s supervision at the Laboratory of Physical Mechanics of the Faculty of Sciences. Paris, may be found in Béghin’s Notice sur les travaux scientifiques de M. Henri Béghin (1943, 1945), at the secretariat of the Academy of Sciences, Paris.