Pierre Ernest Weiss (25.03.1865-24.10.1940) was a French physicist and a member of the Paris Academy of Sciences (1926). He was born in Mulhouse. In 1883-87 he studied at the University of Zurich. In 1889—1902 he was professor at the University of Lyon, in 1902—18 at the Zurich Polytechnic and in 1918 —40 at the University of Strasbourg, where he was director of the Institute of Physics.
His research was in the field of magnetism. He developed a phenomenological theory of ferromagnetism, predicted and investigated the anomaly of the heat capacity and the magnetocaloric effect in ferromagnets, and established (1907) the law of the dependence of the magnetic susceptibility of paramagnets on temperature above the Curie point (the Curie–Weiss law). He was the author of the hypothesis (1907) that an internal interaction exists in ferromagnets which gives rise to spontaneous magnetisation (regions of spontaneous magnetisation, or Weiss domains). He predicted (1911) the existence of a quantum of magnetic moment, which he called the magneton. In 1918, together with A. Piccard, he discovered the magnetocaloric effect.