Josef Stefan was appointed lecturer in mathematical physics at Vienna in 1858 and became a professor there in 1866. In 1866 he bacame director of the Physical Institute at Vienna.
He showed empirically, in 1879, that total radiation from a blackbody is proportional to the fourth power of its absolute temperature. Boltzmann, one of his students, showed in 1884 that this Stefan-Boltzmann law could be demonstrated mathematically. Stefan then applied it to determine the approximate temperature of the surface of the Sun. He also did important work on heat conduction in fluids and the kinetic theory of heat.
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Bron: http://www-history.mcs.st-andrews.ac.uk/history/Mathematicians/Stefan_Josef.html