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# Joseph Stefan

Joseph Stefan (Slovene Jožef Stefan) (March 24, 1835 - January 7, 1893) was a Slovene mathematician, physicist and poet.

 Nekaj bode zmeraj še ostalo, There always something will remain, da ne bomo vedeli, zakaj? that we shall not know, why? Jožef Stefan, Naturoznanske poskušnje (The Science of Nature trials), 1859

Stefan was born in an outstkirt village St. Peter[?] (Slovene Sveti Peter) near Klagenfurt (Slovene Celovec) in Austria-Hungary (now in Austria) to father Aleš (Aleksander) Stefan, born in 1805 and mother Marija Startinik, born 1815. Parents got married when Jožef was eleven. Stefans were modest family. Father was a milling assistant and mother served as a maidservant. Stefan's father died in 1872 and mother almost ten years earlier in 1863.

Stefan attended elementary school in Klagenfurt, where he showed his talent and there they recommended him to continue his schooling, so in 1845 he went to Klagenfurt gymnasium. He experienced the revolutionary year of 1848, as a thirteen-year-old boy, which inspired him to be sympathetic toward Slovene literary[?] production.

When he had finished gymnasium as the best student in his class he thought for a while joining the Benedictine order but he soon abandoned his idea, because his great interest for physics prevailed, and left for Vienna in 1853 to study mathematics and physics. His professor of physics in gymnasium was Karel Robida who wrote the first Slovene physics textbook. Stefan then graduated in mathematics and physics at the University of Vienna in 1857. During his student years, he also wrote and published a number poems in Slovene. He taught physics at the University of Vienna, was Director of the Physical Institute from 1866, Vice-President of the Vienna Academy of Sciences and member of several scientific institutions in Europe.

He published nearly 80 scientific articles, mostly in the Bulletins of the Vienna Academy of Sciences and he is best known for originating a physical power law in 1879 stating that the total radiation from a blackbody j* is proportional to the fourth power of its thermodynamic temperature T:

$j^{\star} = \sigma T^{4}$

The law was later in 1884 derived theoretically in the frame of the thermodynamic by Ludwig Boltzmann and hence known as the Stefan-Boltzmann law. Boltzmann treated a heat engine with the light as a working matter. This law is the only physical law of the nature named after one Slovene physicist. Today we derive the law from the Planck's Law of Radiation:

$j^{\star} = \int_{0}^{\infty} \left( {dj^{\star}\over d\lambda} \right) d\lambda$

and is valid only for ideal black objects. With his law Stefan determined the temperature of the Sun's surface and he got a value of 5430 °C. This was the first sensible value for the temperature of the Sun.

Stefan provided the first measurements of the thermal conductivity of gases, treated evaporation and among others studied diffusion, heat conduction[?] in fluids. For his treatise on optics he received the Richard Lieben award from the University of Vienna. Based on his calculations of diffusion, modern meteorologists have found a flow between the droplets of water and ice crystals, today named Stefan's flow[?].

Very important are also his electromagnetic equations[?], defined in vector notation, and works in the kinetic theory of heat. He was among the first physicists in Europe who fully understood Maxwell's electromagnetic theory and one of the few outside of England who widened it. He calculated inductivity of a coil with a quadratic cross-section, and he corrected Maxwell's miscalculation. He also researched a phenomenon where high-frequency electric current is higher on the surface of conductor than in its interior.

In mathematics the Stefan's tasks[?] with movable boundary is well known. Stefan solved such a task when he was calculating how quickly a layer of an ice on the water grows.

He died in Vienna, Austria-Hungary.

His life and work is extensively studied by physicist Janez Strnad.

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