John Hasbrouck Van Vleck (13.03.1889-27.10.1980) was an American theoretical physicist and a member of the National Academy of Sciences (1935). He was born in Middletown. He graduated from the universities of Wisconsin (1920) and Harvard (1922). In 1923-28 he worked at the University of Minnesota, in 1928 —34 he was professor at the University of Wisconsin and in 1935 — 69 at Harvard. His research was in the field of the quantum theory of atomic structure, magnetism, the theory of valence, the study of atomic and molecular spectra, and ferromagnetic and ferrimagnetic resonance. He was one of the creators of the modern ideas about the magnetism of matter. He developed the quantum-mechanical theory of diamagnetism and paramagnetism (1926 — 28), obtained the paramagnetic addition to the diamagnetic susceptibility of asymmetric atoms and molecules, called Van Vleck paramagnetism (1927), and extended the theory of the crystal (ligand) field. He gave a detailed treatment of antiferromagnetism (1941) and a thermodynamic theory of the molecular field for antiferromagnets, extended Heisenberg's model of localised spins and proposed an effective spin Hamiltonian. He constructed (1940 — 41) the theory of the spin-lattice relaxation of paramagnetic ions in crystals due to the spin-orbit interaction and to the modulation of the crystal field by lattice vibrations (the Kronig–Van Vleck mechanism). He predicted the phonon bottleneck effect in the spin-lattice relaxation of paramagnetic ions at low temperatures, and introduced the concept of spin temperature in the problem of the dynamic polarisation of nuclei. He discovered a new type of anisotropic interaction connected with the spin-orbit interaction of electrons, and constructed a microscopic theory of magnetic anisotropy. Nobel Prize (1977). A member of many academies of sciences and scientific societies. President of the American Physical Society (1952-53). The A. Michelson (1963) and I. Langmuir (1965) medals, the National Medal of Science (1967) and others.