Jozef Stefan discovers the Stefan–Boltzmann law

Background. Josef Stefan, a Carinthian Slovene physicist of the Austrian Empire, is credited with originating Stefan's law. The law describes the intensity of thermal radiation emitted by matter, stating that total radiation from a black body is proportional to the fourth power of its thermodynamic temperature. This empirical finding was based on Tyndall's experimental measurements.

Empirical Derivation. Stefan deduced the proportionality to the fourth power of absolute temperature in 1877 using Tyndall's experimental data. He published this relationship in the article 'Über die Beziehung zwischen der Wärmestrahlung und der Temperatur' in the Bulletins from the sessions of the Vienna Academy of Sciences. This work established the empirical basis for what is now known as Stefan's law.

Legacy and Naming. The law is named for Josef Stefan, who empirically derived the relationship, and Ludwig Boltzmann, who derived the law theoretically in 1884. While Stefan's work was empirical, Boltzmann's later theoretical derivation extended the law to apply to grey-body emissions, leading to the combined name Stefan–Boltzmann law.