Perrin, Jean Baptiste (zhäN bätēstˈ pĕrăNˈ) [key], 1870–1942, French physicist. From 1910 to 1940 he was professor at the Univ. of Paris, and in 1941 he came to the United States. Perrin specialized in the Brownian movement of particles. For his work on the discontinuous structure of matter and for his discovery of the equilibrium of sedimentation (which permitted an accurate calculation of the size of atoms), he received the 1926 Nobel Prize in Physics. He is noted also for his work on X rays and cathode rays. His works include Atoms (1903, tr. 1923). His son, Francis Henri Perrin, 1901–92, became a director of the French atomic energy commission when it was established in 1946. In 1951, Perrin took over as the organization's high commissioner of atomic energy, following Frédéric Joliot-Curie's dismissal.