Langevin, Paul

(1872-1946)

   physicist

   Paul Langevin, who is credited with the first successful development of sonar, as well as the development of a modern theory of magnetism, was born in Paris. He attended the École Lavoisier and École de physique et de chimie industrielles, and also the École normale superiéure, where he studied with the noted physicist jean perrin. Additionally, Langevin studied at Cambridge University under the leading British physicist, J. J. Thompson, and at the sorbonne under pierre curie. He held professorships in physics at the Collège de France (1904) and at the Sorbonne (1909). Langevin's work on ionized gases led him to studies of magnetism and the properties of magnetic fields. in 1911, he proposed a theory to support Pierre Curie's work on paramagnetic gases, and his studies later influenced the Danish physicist Niels Bohr in that scientist's development of the structure of the atom. During World War I (1915), Langevin worked on developing a method for detecting submarines by echolocation (later known as "sonar"), and he also found a method for measuring ultrasonic sound waves. In 1938, he developed a method for slowing fast neutrons. This would later be used by physicists who attempted to develop atomic reactors. During World War II, Langevin was an outspoken critic of Nazi Germany, and was imprisoned in a concentration camp after the German invasion of France (1940). He escaped to Switzerland (1944) and, returning to Paris after the war, assumed the post of director of the Collège de France. Langevin was named to the Academy of Sciences in 1934.