Langevin, Paul

Born Jan. 23, 1872, in Paris; died there Dec. 19, 1946 (remains transferred to the Pantheon). French physicist and public figure. Member of the Paris Academy of Sciences (1934), honorary member of the Academy of Sciences of the USSR (1929), and member of the London Royal Society. Son of C. P. Langevin.

P. Langevin graduated from the Ecole de Physique et Chimie Industrielles in 1891 and the Ecole Normale in Paris in 1897. Upon graduation from the latter, he received a stipend from the city of Paris and worked for one year at the Cavendish Laboratory in Cambridge under J. J. Thomson, whom he considered to be, along with P. Curie and L. Brillouin, his mentor. After his return to France, he taught at the University of Paris. In 1902 he began working at the Collège de France (professor from 1909); at the same time, beginning in 1905, he occupied the chair at the Ecole de Physique et Chimie Industrielles vacated by the departure of P. Curie. Langevin became director of this school in 1925 and reorganized it into an institution of higher learning in 1926.

The scientific activities of Langevin, who for decades was considered to be the leader of physics in France, developed in various directions. His earliest work dealt with the study of ionization in gases, which constituted the subject of his dissertation (1902). Proceeding from the kinetic theory of gases, he developed the theory of motion of charged ions in gases and demonstrated that heavy positive ions are formed during ionization along with light negative ions. He introduced the concept of the probability of recombination and developed methods for the determination of ion mobility. His most important works are devoted to the theory of magnetic phenomena. On the basis of electronic concepts, he developed (1903–05) the statistical theory of diamagnetic and paramagnetic phenomena and interpreted the laws of magnetism, which were determined experimentally by Curie; he also developed (1910) the theory of double refraction in electric and magnetic fields. This work represented the first attempt to apply statistical physics to the study of magnetic properties of matter. The statistical method developed by him subsequently found wide application.

Langevin made significant contributions to the development of the dynamics of electrons (1904) and to the development of various problems in the theory of relativity and relativistic electrodynamics. Langevin also dealt with the theory of Brownian motion and other problems of theoretical physics. Louis de Broglie wrote his dissertation on the wave nature of matter under Langevin’s direction. Of greatest significance in applied physics was Langevin’s proposal concerning the use of piezoquartz for the generation of ultrasonic oscillations, which was utilized by Langevin and his co-workers for underwater signalization and detection (location of submarines) during World War I.

Langevin’s public activities were of great progressive value. He was an active member of the League of the Rights of Man, founded in 1898. One of the founders of the Circle of Friends of New Russia (1919), he advocated the development of cultural ties with the Soviet Union. In 1920 he fought for amnesty for those involved in the mutiny in the French fleet in the Black Sea (1919). In the 1930’s he actively supported the Popular Front. A pacifist, he headed the Antifascist Vigilance Committee of Intellectuals (from 1934). He founded (1939) and directed the progressive sociopolitical journal La Pensée. On Mar. 20, 1940, he appeared before a military tribunal to defend 44 Communist deputies who had been illegally arrested. Langevin was arrested in October 1940 by the fascist German occupiers and deported in December 1940 to Troyes, where he lived under police surveillance. In May 1944, Langevin fled to Switzerland with the help of the Resistance. Upon his return to liberated France in September 1944, he joined the Communist Party. Langevin was elected chairman of the France-USSR Society in 1946.