Stefan J
NAME: Stefan, Josef
ACHIEVEMENT(S): Stefan-Boltzmann Law.
NICKNAME/ALIAS: None
DATE/PLACE OF BIRTH: 24 March 1835, at Klagenfurt, Austria
DATE/PLACE/AGE AT DEATH: 7 January 1893, in Vienna, Austria. Aged 57
DISCIPLINE: Physicist
FIELD: Physics
LANGUAGE: Austrian
PARENTS: ?
SIBLINGS: ?
SPOUSE: ?
CHILDREN: ?
EDUCATION: Klagenfurt Gymnasium, to 1853; University of Vienna, 1853-57
MAJOR WORK: ?
LIFE AND TIMES: After graduation Stefan spent a year working as a teacher while working with <worked with> Ludwig* on the flow of water through tubes. In 1858 he was appointed junior lecturer at the University of Vienna, rising to professor of higher mathematics and physics in 1863.
He held this position for the rest of his life, and also became Director of the Institute for Experimental Physics at Vienna (founded by <directed institute of> Doppler* in 1850) in 1866.
During the 1870s, Stefan's work at Vienna was concerned with the kinetic theory of gases, particularly diffusion.
He also studied electromagnetic induction and thermomagnetic effects, advanced a theory of magnetism, and worked on optical interference phenomena, capillarity, and the thermal conductivity of gases. His most famous achievement (the discovery of the radiation law) came in 1879.
As early as 1740 it had been known that Newton's law of cooling (the rate of cooling of a hot body is proportional to the difference in temperature between the body and its surroundings) while OK up to 50C, was incorrect for large temperature differences. Many experimenters had during the 18th and 19th centuries discovered that the amount of heat given out by a very hot body is far greater than expected by Newton's law.
In the 1860s the Irish physicist John Tyndall had measured the amount of radiant heat produced by a platinum wire heated to varying degrees of incandescence by an electric current. Tyndall had found that over the greatest range, from about 525C up to about 1200C, the intensity of radiation increased by 11.7 times.
Analyzing Tyndall's results, Stefan realized that this increase in intensity was equal to the ratio of the absolute temperature raised to the fourth power, and from this deduced his radiation law, which states that the total energy radiated in a given time by a given area of a body, E, is equal to sigma]T[to the power of]4, where T is the absolute temperature and [sigma] is a proportionality constant now known as the Stefan constant. Stefan confirmed the validity of this result over wide temperature ranges.
In 1884, one of Stefan's former students, <taught> Boltzmann* gave a theoretical explanation of Stefan's law based on thermodynamic principles and James Clerk Maxwell's kinetic theory. It was Boltzmann who established that Stefan's law held only for perfect black bodies (theoretical surfaces that absorb all incident heat radiation), and that Stefan had in fact been able to derive the law only because platinum approximates to a black body.
Using the law (later verified by the German physicists <his law verified by> Pringsheim* and Otto Lummer in 1896 and now known as the Stefan-Boltzmann Law) Stefan was able to make the first accurate calculation of the surface temperature of the Sun (approximately 6000C).
During the 1880s, Stefan made several other contributions to physics, his accurate measurements of the conductivity of gases helping to confirm <confirmed theory of> Maxwell's* kinetic theory.
He also made studies on heat conduction in fluids, on ice formation, on dissolving, and on the relationship between surface tension and evaporation.
Finally, he published many works on acoustics, and presided over the International Conference on Musical Pitch held in Vienna in 1885, which established standard pitch at 435 cycles per second for central and eastern Europe.
In the same year, Stefan was appointed vice-president of the Imperial Academy of Sciences, a post he held until his death.
ASSESSMENT: The Stefan-Boltzmann Law was a major discovery in physics.
EXTRA CONNECTIONS: His work related to that of physicist <work related to> Planck*
ONELINER: Josef Stefan, 19th-century physicist
BIBLIOGRAPHY:
DSB, EB