Gregory Breit (born 14.07.1899) is an American physicist and a member of the National Academy of Sciences (1939). He was born in Nikolaev. He graduated from Johns Hopkins University (1920). In 1921-29 he worked at Leiden and Minnesota universities and at the Carnegie Institute of Technology. In 1929 — 34 he was professor at New York University, in 1934—47 at the University of Wisconsin, in 1947—68 at Yale University, and in 1968 — 74 at the University of Buffalo. His research concerned nuclear physics, the study of nuclear structure and of the properties of nuclear forces, scattering theory, quantum theory, quantum mechanics, quantum electrodynamics, the theory of accelerators and high-energy physics. He developed (1933) the first quantum-mechanical theory of the Hanle effect. In 1936, with E. Condon and R. Present, he put forward the hypothesis of the isotopic invariance of nuclear forces, drawing attention to the equivalence of the “proton — neutron” and “proton — proton” forces; together with E. Wigner he proposed the dispersion formula for nuclear reactions (the Breit-Wigner formula), and with E. Condon he developed the first theory of proton-proton scattering. With I. Rabi he was the first to point out that the spins and magnetic moments of nuclei can be measured by studying the deflection of atomic beams. He gave an explanation (1947 — 48) of the anomalous magnetic moment of the electron. He was one of the pioneers of accelerator technology. The B. Franklin Medal (1964), the National Medal of Science (1967), the T. Bonner Prize (1969).