Paul Langevin

Studying under Pierre Curie at the ESPCI in Paris and J.J. Thomson at the Cavendish Laboratory in Cambridge, Langevin became professor of physics at the Collège de France. In 1905, he published his modern electronic theory of magnetism, and in 1908, the Langevin equation.

During World War I, utilizing Pierre Curie's piezoelectric quartz crystals, Langevin invented the first ultrasonic sonar (ASDIC), emitting high-frequency acoustic pulses to detect submerged German submarines, founding modern medical ultrasound. An outspoken anti-fascist, he was arrested by the Gestapo in 1940 and escaped to Switzerland.