Jeans, James Hopwood (11.09.1877–16.09.1946) was an English physicist and astrophysicist and a Fellow of the Royal Society (1906). Born in London. Graduated from the University of Cambridge (1900) and worked there in 1901–04 and 1910–12; in 1905–09 he was professor at Princeton University, in 1923–44 a research associate at the Mount Wilson Observatory (USA), and in 1924–29 and 1934–39 professor at the Royal Institution (London).
His main work in physics concerned the kinetic theory of gases and the theory of thermal radiation. His book “The Dynamical Theory of Gases”, which ran through several editions (the first in 1904), was widely read in its day. In the theory of the thermal radiation of a black body he used Rayleigh's method of the equal distribution of energy and derived in 1905 a formula for the energy density (the Rayleigh–Jeans law). Built on classical physics, this formula proved inapplicable to the whole radiation spectrum; it agreed with experiment only for long wavelengths. Jeans also worked on quantum theory, the mathematical theory of electricity and magnetism, theoretical mechanics and relativity.
Jeans's astrophysical research was in the field of the equilibrium figures of rotating fluid bodies, the structure and evolution of stars and of stellar systems, and the origin of the Solar System. In the 1920s and 1930s his cosmogonic hypothesis of the origin of our planetary system became widely known. According to this hypothesis the Solar System was formed when another star, passing close to the Sun, tore out of it a cigar-shaped filament of matter which, breaking into pieces, gave “life” to the planets. The Soviet scientist N. N. Pariysky showed this “catastrophic hypothesis” to be untenable.
Jeans was one of the leaders of the Cambridge school of modern physical idealism. He wrote many popular science books.
The Royal Medal (1919), the B. Franklin Medal (1931) and others.