Cossert, Eugène Maurice Pierre

(b. Amiens, France, 4 March 1866; d. Toulouse, France, 31 May 1931)

geometry, mechanics, astronomy.

Cosserat first studied at Amiens. When he was seventeen, he was accepted at the École Normale Superieure. His scientific career was spent in Toulouse: he was assigned to the observatory in 1886, became professor of differential calculus at the Faculty of Sciences in 1896 and of astronomy in 1908, and was director of the observatory from 1908 until his death. A reserved, kindly man and a diligent worker, Cosserat was one of the moving forces of the University of Toulouse for thirty-five years. He was a membre non-résident of the Académie des Sciences (1919) and a corresponding member of the Bureau des Longitudes (1923).

For the first ten years Cosserat divided his time between his duties at the observatory, where he made equatorial observations of double stars, planets, and comets, and his research in geometry. His doctoral thesis (1888), which deals with an extension of Plucker’s concept of the generation of space by means of straight lines, considers the infinitesimal properties of space created by circles. The congruences and complexes of straight lines are the main subject of his later works, in which he remained a disciple of Darboux.

In studying the deformation of surfaces Cosserat was oriented toward the theory of elasticity and the general problem of continuous mediums. These studies were done between 1885 and 1914 in collaboration with his older brother François, who was chief engineer of the Service des Ponts et Chaussées. François was the main participant in tests on synthesis and philosophical concepts, the mathematical framework of the research being furnished by Eugène.

The most practical results concerning elasticity were the introduction of the systematic use of the movable trihedral and the proposal and resolution, before Fredholm’s studies, of the functional equations of the sphere and ellipsoid. Cosserat’s theoretical research, designed to include everything in theoretical physics that is directly subject to the laws of mechanics, was founded on the notion of Euclidean action combined with Lagrange’s ideas on the principle of extremality and Lie’s ideas on invariance in regard to displacement groups. The bearing of this original and coherent conception was diminished in importance because at the time it was proposed, fundamental ideas were already being called into question by both the theory of relativity and progress in physical theory.

The Toulouse observatory participated in the international undertaking of formulating the Carte du Ciel. Having become director, Cosserat organized the important work of meridian observations, photography, and computation of positions in order to make systematic determination of the proper motions of the stars. He personally supervised the details of these operations, including the computations, and was completely occupied with this task for the last fifteen years of his life.

Cosserat was particularly concerned with accuracy: he used his original research, which later appeared as notes in the now-classic works of Darboux, Koenigs, Appell, and Chwolson. Thus, although his name seldom appears in modern works, his influence on them was far-reaching.

BIBLIOGRAPHY

I. Original Works. In geometry and analysis, Cosserat’s main works were published in Annales de la Faculté des sciences de Toulouse: “Sur le cercle considéré comme élément générateur de l’espace,” 3 (1889), E1-E81, his doctoral thesis; “Formes bilineaires,” ibid., M1-M12; “Courbes algebriques dans le voisinage d’un de ses points,” 4 (1890), O1-O16; “Congruences de droites et la théorie des surfaces,” 7 (1893), N1-N62; “Déformations infinitésimales d’une surface flexible et inextensible,” 8 (1894), E1-E46; and “Travaux scientifiques de T. J. Stieljes,” 9 (1895), [1]-[64]; in Mémoires de l’Academie des sciences de Toulouse: “Classe de complexes de droites,” 4 (1892), 482–510; and “Théorie des lignes tracées sur une surface.” 7 (1895), 366–394; in Comptes rendus de l’Académie des sciences, some twenty notes (1888–1908), most notably “Sur les courbes algebriques à torsion constante et sur les surfaces minima…,” 120 (1895), 1252–1254; and “Sur la théorie des èquations aux dérivées partielles du deuxième ordre,” in G. Darboux, Leçons sur la théorie des surfaces, IV (Paris, 1896), 405–422.

In mechanics he wrote, with his brother François: “Théorie de l’ésasticite,” in Annales de la Faculté des sciences de Toulouse, 10 (1896), II-Ill6; “Note sur la cinématique d’un milieu continu,” in G. Koenigs, Leçons de cinématique (Paris, 1897), pp. 391–417; “Note sur la dynamique du point de du corps invariable,” in O. Chwolson, Traité de physique, I (Paris, 1906), 236–273; “Note sur la théorie de l’action euclidienne,” in P. Appell, Traité de mécanique rationnelle, III (Paris, 1909), 557–629; and “Note sur la théorie des corps déformables,” in O. Chwolson, Traité de physique, II (Paris, 1909), 953–1173, also published separately (Paris, 1909).

In astronomy he wrote “Sur quelques étoiles dont le mouvement propre annuel dépasse 0˝5,” in Comptes rendus de l’Académie des sciences, 169 (1919), 414–418; and “Déterminations photographiques de positions d’etoiles,” in Annales de l’Observatoire de Toulouse, 10 (1933), 1–306.

II. Secondary Literature. On Cosserat or his work, see P. Caubet, “E. Cosserat: set vues générales sur I’astronomie de position,” in Journal des observateurs, 14 (1931), 139–143; and L. Montangerand, “Éloge de Coserat,” in Annales de l’Observatoire de Toulouse, 10 (1933), xx-xxx.

Jacques R. LÉvy