Boltzmann, Ludwig (lŏtˈvĭkh bôltsˈmän) [key], 1844–1906, Austrian physicist, b. Vienna, educated at Univ. of Vienna. He began teaching (1869) at Graz Univ. In 1873 he became mathematics professor at Vienna and then physics professor at Graz (1876), Munich (1890), Vienna (1895), and Leipzig (1900). Boltzmann made important contributions to the kinetic theory of gases and to statistical mechanics—the Boltzmann constant, which relates the mean total energy of a molecule to its absolute temperature, is used widely in statistics and is named for him. Working independently, he demonstrated a law on blackbody radiation that had been stated by the Austrian physicist Josef Stefan; hence the law is sometimes known as the Stefan-Boltzmann law.
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