Paul Langevin (1872-1946), French physicist. Langevin was educated in France, before spending a year at the Cavendish laboratory in Cambridge, UK. His main work was in the field of paramagnetism, which is the mild attraction of materials to magnetic fields. He deduced a formula correlating paramagnetism with absolute temperature. During the First World War he worked on the use of ultrasonic waves in submarine detection, research which would later culminate in the development of sonar.