Josef Stefan (or Jožef Štefan) (March 24, 1835 to Jan 7, 1893) Stefan was an Austrian physicist and mathematician of Slovenian ethnicity. When young he considered entering the Catholic priesthood as a member of the Benedictine order, but his interest in physics led him into scientific research instead. His most famous discovery was the Stefan-Boltzmann Law (also called Stefan’s Law), which states that the energy radiated by a “black body” is proportional to the fourth power of its absolute temperature: j = σ T4, where the coefficient σ is called the Stefan-Boltzmann constant. (The great physicist Boltzmann was Stefan’s student.) Stefan made many other contributions on topics including heat conduction, diffusion, evaporation, and phase transitions. These contributions are reflected in the large number of physics concepts named after him, including Stefan flow, Stefan problem, Stefan equation, Stefan formula, and Stefan number. Also named after him is the famous Institut Jožef Štefan, the largest research center in Slovenia.