STEFAN, Jožef (Joseph)

S.’s childhood was marked with poverty, heavy physical work and appurtenance to Slovenian minority. As an excellent student at grammar school in Klagenfurt and later of mathematics and physics at the University of Vienna (1853-1858), he was also very active in the literary field, writing poems in the Slovenian language and publishing them in many newspapers.
After achieving habilitation, he decided to engage in scientific work and he began working at the Physical Institute. From then on he lived in Vienna and devoted his life to research, teaching, scientific and organizational work. In 1860 he was elected correspondent member and in 1866 a regular member by the Austrian Academy of Sciences. In 1863 he was the youngest university professor in Austria. As Director of Physical Institute (from 1866 on), S. dealt with all areas of physics: mechanics, optics, acoustics, magnetism and electricity.
In the field of mechanics he cooperated with K. Ludwig in the study of liquids and explored the vibration of elastic rods and strings. He also took interest in the diffusion in liquids and gases, he challenged Ernst→Mach thesis and unlike him defended the atomic structure of matter. In the field of acoustics he invented a method for determining the speed of sound in gases and solids. In 1885 he as Vice President of the Academy of Sciences chaired the International Conference on acoustics. In optics he was mainly interested in the polarization of light, interferences and the development of methods for measuring the wavelength of light. His most significant contributions were in the field of thermostatic: he researched the thermal conductivity of gases and developed a device for their experimental determination. This focused his attention on the field of radiation. In 1879 he originated the physical power law named after him which states that the total radiation from a black body is proportional to the fourth power of its thermodynamic temperature. The constant in a mathematical formula of this law is called the S.‘s constant. With his law S. determined the temperature of the Sun's surface and he calculated a value of around 6000 °C.
In 1884 Ludwig →Boltzmann theoretically justified the law of his teacher and predecessor. Therefore, the law is often named after the both scientists as S.-Boltzmann law. After S. and →Boltzmann, Max Planck and Albert Einstein also took interest in the study of radiation and it has led them to further discoveries.
In his late years S. was dealing primarily with electricity and magnetism. He made an important contribution to the thermodynamics and was among the first physicists in Europe who fully understood Maxwell's electromagnetic theory. He also researched a phenomenon called the skin effect, which is still named after him, where high-frequency electric current is greater on the surface of a conductor than in its interior. In addition to his scientific theory, S. is also known as an inventor of thermoelectric engines and defining the maximum electromagnetic power and he was also a good organizer. In 1883 S. acted as co-founder of Electrical Association in Vienna and was its chairman until 1886. This association nowadays awards the S. medal for outstanding achievements in the field of theory and practice of electrical engineering. In 1883 he as a president led the scientific committee to the International Electricity Exhibition in Vienna. In the meantime he managed an international group of eminent scientists, which, inter alia, developed a modern electrical measurement technique
at the University of Vienna in one of the best equipped physical laboratories in the world. S.‘s last paper is dedicated to the study of electromagnetic waves. He belongs to the last generation of scientists who dealt with all areas of their profession. S. is considered the founder of the Austrian physical school which had a significant impact on all the successor states of Austria-Hungary. The most important Slovenian Physical Institute is named after him.