Josef Stefan
Josef Stefan (Slovene Jožef Štefan) was a physicist, mathematician, and poet from the Austrian Empire. Born on March 24, 1835, in St. Peter near Klagenfurt to a modest Slovenian family, he showed talent early and pursued math and physics in Vienna from 1853. He earned his habilitation in mathematical physics in 1858 and spent much of his career at the University of Vienna, becoming Director of the Physical Institute in 1866 and Vice-President of the Vienna Academy of Sciences. He died in Vienna on January 7, 1893.
Stefan is best known for Stefan’s law, also called the Stefan–Boltzmann law. It states that the total energy radiated by a black body is proportional to the fourth power of its temperature. He first derived this in 1879, and in 1884 his student Ludwig Boltzmann extended the idea to grey bodies (real, imperfect emitters). Stefan also studied heat conduction, evaporation, diffusion, and the flow of matter caused by evaporation (now called Stefan flow). He contributed to the theory of moving boundaries, known as Stefan problems.
He helped advance the understanding of electromagnetism and the kinetic theory of heat, and he corrected some earlier calculations about electrical currents and the skin effect. Stefan even estimated the Sun’s surface temperature, arriving at about 5,430°C, which was an important early result.
Stefan published around 80 scientific papers and mentored notable scientists such as Ludwig Boltzmann, Marian Smoluchowski, and Johann Josef Loschmidt. He received the Lieben Prize in 1865 and, besides science, wrote poems in Slovene. His legacy lives on in many scientific terms and institutions, including the Jožef Stefan Institute in Slovenia.
This page was last edited on 3 February 2026, at 14:08 (CET).