An Austrian physicist, whose original contributions ranged over several important fields, including the kinetic theory of gases, hydrodynamics and in particular, radiation, Stefan was born on March 24, 1835 at St. Peter near Klagenfurt and died on January 7, 1893 in Wien.
Stefan was educated at the University of Wien, receiving his doctor of philosophy in 1858, then became Privatdozent in Mathematical Physics, in 1863 Professor Ordinarius of Physics and in 1866 Director of the Physical Institute. He was a distinguished member of the Academy of Sciences Wien, of which he was appointed secretary in 1875. Before Stefan's work, G. R. Kirchhoff had already described the perfect radiator as the "Perfect Black Body", namely, one that absorbed all the radiation that fell on it and reflected none, but emitted radiation of all wavelengths. Stefan showed empirically in 1879 that the radiation of such a body was proportional to the fourth power of its absolute temperatures, a relationship known as the "Stefan and Boltzmann" law after it had been deduced by L. Boltzmann in 1884 from thermodynamic considerations.
In the year 1891 Stefan published his work on the formation of ice in the Polar Seas, giving a special solution of this nonlinear conduction problem with phase change (the more general solution being due to F. Neumann).