Born Mar. 28, 1865, in Mulhouse; died Oct. 24, 1940, in Lyon. French physicist. Member of the Paris Academy of Sciences (1926).
Weiss studied at the University of Zürich (1883-87) and at the Ecole Normale in Paris (1888-92). From 1899 he was a professor at the University of Lyon; and from 1903, at the Swiss Federal Polytechnic School in Zürich. From 1918 to 1940 he was a professor in Strasbourg. His major works deal with magnetism. In 1907, Weiss stated a hypothesis on the existence of internal interaction in ferromagnetic materials leading to spontaneous magnetization. He developed a phenomenological theory of ferromagnetism and also theoretically predicted and experimentally studied the anomaly of heat capacity and the magnetocaloric effect of ferromagnets. Weiss also discovered the law for the temperature dependence of the susceptibility of ferromagnets above the Curie point (the Curie-Weiss law). In 1911 he concluded that atoms have magnetic moment, which he termed magneton. Weiss constructed powerful electromagnets and numerous devices for magnetic and electrical measurements.