Joseph Stefan
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Josef Stefan ( sl, Jožef Štefan; 24 March 1835 – 7 January 1893) was an ethnic
Carinthian Slovene Carinthian Slovenes or Carinthian Slovenians ( sl, Koroški Slovenci; german: Kärntner Slowenen) are the indigenous minority of Slovene ethnicity, living within borders of the Austrian state of Carinthia, neighboring Slovenia. Their status of ...
physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate caus ...
, mathematician, and poet of the
Austrian Empire The Austrian Empire (german: link=no, Kaiserthum Oesterreich, modern spelling , ) was a Central-Eastern European multinational great power from 1804 to 1867, created by proclamation out of the realms of the Habsburgs. During its existence, ...
.


Life and work

Stefan was born in an outskirt village of St. Peter (Slovene: ; today a district of
Klagenfurt Klagenfurt am WörtherseeLandesgesetzblatt 2008 vom 16. Jänner 2008, Stück 1, Nr. 1: ''Gesetz vom 25. Oktober 2007, mit dem die Kärntner Landesverfassung und das Klagenfurter Stadtrecht 1998 geändert werden.'/ref> (; ; sl, Celovec), usually ...
) in the
Austrian Empire The Austrian Empire (german: link=no, Kaiserthum Oesterreich, modern spelling , ) was a Central-Eastern European multinational great power from 1804 to 1867, created by proclamation out of the realms of the Habsburgs. During its existence, ...
(now in Austria) to father Aleš (Aleksander) Stefan, born in 1805, and mother Marija Startinik, born 1815. His parents, both ethnic Slovenes, married when Josef was eleven. The Stefans were a modest family. His father was a milling assistant and his mother served as a maidservant. Stefan's mother died in 1863 and his father in 1872. Josef was their only child. Stefan attended elementary school in Klagenfurt, where he showed his talent. They recommended to him to continue his schooling, so in 1845, he went to . As a thirteen-year-old boy, he experienced the revolutionary year of 1848, which inspired him to be sympathetic toward Slovene literary production. After having graduated top of his class in high school, he briefly considered joining the
Benedictine Order , image = Medalla San Benito.PNG , caption = Design on the obverse side of the Saint Benedict Medal , abbreviation = OSB , formation = , motto = (English: 'Pray and Work') , foun ...
, but his great interest in physics prevailed. He left for Vienna in 1853 to study
mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
and
physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
. His professor of physics in the gymnasium was
Karel Robida Karel may refer to: People * Karel (given name) * Karel (surname) * Charles Karel Bouley, talk radio personality known on air as Karel * Christiaan Karel Appel, Dutch painter Business * Karel Electronics, a Turkish electronics manufacturer * Gr ...
, who wrote the first Slovene physics textbook. Stefan then earned his
habilitation Habilitation is the highest university degree, or the procedure by which it is achieved, in many European countries. The candidate fulfills a university's set criteria of excellence in research, teaching and further education, usually including a ...
in
mathematical physics Mathematical physics refers to the development of mathematics, mathematical methods for application to problems in physics. The ''Journal of Mathematical Physics'' defines the field as "the application of mathematics to problems in physics and t ...
at the
University of Vienna The University of Vienna (german: Universität Wien) is a public research university located in Vienna, Austria. It was founded by Duke Rudolph IV in 1365 and is the oldest university in the German-speaking world. With its long and rich histor ...
in 1858. During his student years, he also wrote and published a number of poems in Slovene. Stefan 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 died in
Vienna en, Viennese , iso_code = AT-9 , registration_plate = W , postal_code_type = Postal code , postal_code = , timezone = CET , utc_offset = +1 , timezone_DST ...
, Austria-Hungary. His life and work have been extensively studied by the physicist
Janez Strnad Janez Strnad (March 4, 1934 – November 28, 2015) was a Slovene physicist and popularizer of natural science. Life and work Strnad was born in Ljubljana, Kingdom of Yugoslavia (now Slovenia). He received a degree at the University of Ljub ...
.


Work

Stefan published nearly 80 scientific articles, mostly in the Bulletins of the Vienna Academy of Sciences. He is best known for originating Stefan's law in 1879, a
physical Physical may refer to: *Physical examination In a physical examination, medical examination, or clinical examination, a medical practitioner examines a patient for any possible medical signs or symptoms of a medical condition. It generally co ...
power law In statistics, a power law is a Function (mathematics), functional relationship between two quantities, where a Relative change and difference, relative change in one quantity results in a proportional relative change in the other quantity, inde ...
stating that the total
radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
from a
black body A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The name "black body" is given because it absorbs all colors of light. A black body ...
is proportional to the fourth power of its
thermodynamic temperature Thermodynamic temperature is a quantity defined in thermodynamics as distinct from kinetic theory or statistical mechanics. Historically, thermodynamic temperature was defined by Kelvin in terms of a macroscopic relation between thermodynamic wor ...
''T'': : j^ = \sigma T^ He derived this law from the measurements of the French physicists Dulong and
Petit Petite or petite may refer to: *Petit (crater), a small, bowl-shaped lunar crater on Mare Spumans * ''Petit'' (EP), a 1995 EP by Japanese singer-songwriter Ua * Petit (typography), another name for brevier-size type *Petit four * Petit Gâteau *P ...
. As both incident radiation and blackbody emission are always equal, this equation applies equally to the temperature of any ideal body subject to incident radiation across its surface. In 1884, the law was extended to apply to grey-body emissions by Stefan's student
Ludwig Boltzmann Ludwig Eduard Boltzmann (; 20 February 1844 – 5 September 1906) was an Austrian physicist and philosopher. His greatest achievements were the development of statistical mechanics, and the statistical explanation of the second law of thermodyn ...
and hence is known as
Stefan–Boltzmann law The Stefan–Boltzmann law describes the power radiated from a black body in terms of its temperature. Specifically, the Stefan–Boltzmann law states that the total energy radiated per unit surface area of a black body across all wavelengths ...
. Boltzmann treated a
heat engine In thermodynamics and engineering, a heat engine is a system that converts heat to mechanical energy, which can then be used to do mechanical work. It does this by bringing a working substance from a higher state temperature to a lower state ...
with light as a working matter. This law is the only physical law of nature named after a Slovene physicist. Today, the law is derived from
Planck's law In physics, Planck's law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature , when there is no net flow of matter or energy between the body and its environment. At ...
of black-body radiation: : j^ = \int_^ \left( \right) d\lambda With his law, Stefan determined the temperature of the Sun's surface, which he calculated to be . This was the first sensible value for the temperature of the Sun. Stefan provided the first measurements of the
thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...
of gases, treated
evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...
, and among others studied
diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
,
heat conduction Conduction is the process by which heat is transferred from the hotter end to the colder end of an object. The ability of the object to conduct heat is known as its ''thermal conductivity'', and is denoted . Heat spontaneously flows along a te ...
in
fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
s. For his treatise on
optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...
, the University of Vienna bestowed the
Lieben Prize The Ignaz Lieben Prize, named after the Austrian banker , is an annual Austrian award made by the Austrian Academy of Sciences to young scientists working in the fields of molecular biology, chemistry, or physics. Biography The Ignaz Lieben Pri ...
on him. Because of his early work in calculating evaporation and diffusion rates, flow from a droplet or particle that is induced by evaporation or sublimation at the surface is now called the Stefan flow. Very important are also his electromagnetic equations, defined in
vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...
notation, and works in the
kinetic theory Kinetic (Ancient Greek: κίνησις “kinesis”, movement or to move) may refer to: * Kinetic theory, describing a gas as particles in random motion * Kinetic energy, the energy of an object that it possesses due to its motion Art and ente ...
of heat. Stefan was among the first physicists in Europe who fully understood
Maxwell's Maxwell's, last known as Maxwell's Tavern, was a bar/restaurant and music club in Hoboken, New Jersey. Over several decades the venue attracted a wide variety of acts looking for a change from the New York City concert spaces across the river. Ma ...
electromagnetic theory In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...
and one of the few outside England who expanded on it. He calculated inductivity of a coil with a quadratic cross-section, and he corrected Maxwell's miscalculation. He also researched a phenomenon called the
skin effect Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor and decreases exponentially with greater depths in the co ...
, where high-frequency
electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...
is greater on the surface of a conductor than in its interior. In mathematics, the
Stefan problem In mathematics and its applications, particularly to phase transitions in matter, a Stefan problem is a particular kind of boundary value problem for a system of partial differential equations (PDE), in which the boundary between the phases can m ...
s or Stefan's tasks with movable boundary are well known. The problem was first studied by Lamé and Clapeyron in 1831. Stefan solved the problem when he was calculating how quickly a layer of
ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...
on water grows ( Stefan's equation).


Eponymous terms

In physics, several concepts are named after Joseph Stefan. In particular: *
Stefan–Boltzmann law The Stefan–Boltzmann law describes the power radiated from a black body in terms of its temperature. Specifically, the Stefan–Boltzmann law states that the total energy radiated per unit surface area of a black body across all wavelengths ...
*
Stefan–Boltzmann constant The Stefan–Boltzmann constant (also Stefan's constant), a physical constant denoted by the Greek letter ''σ'' (sigma), is the constant of proportionality in the Stefan–Boltzmann law: "the total intensity radiated over all wavelengths inc ...
σ * Stefan adhesion *
Stefan problem In mathematics and its applications, particularly to phase transitions in matter, a Stefan problem is a particular kind of boundary value problem for a system of partial differential equations (PDE), in which the boundary between the phases can m ...
* Stefan's equation * Stefan's formula * Stefan flow *
Stefan number The Stefan number (St or Ste) is defined as the ratio of sensible heat to latent heat. It is given by the formula \mathrm = \frac, where * ''cp'' is the specific heat, ** cp is the specific heat of solid phase in the freezing process while cp ...
* Stefan tube *
Maxwell–Stefan diffusion The Maxwell–Stefan diffusion (or Stefan–Maxwell diffusion) is a model for describing diffusion in multicomponent systems. The equations that describe these transport processes have been developed independently and in parallel by James Clerk Max ...
The
Jožef Stefan Institute The Jožef Stefan Institute (IJS, JSI) ( sl, Institut "Jožef Stefan") is the largest research institute in Slovenia. The main research areas are physics, chemistry, molecular biology, biotechnology, information technologies, physics, reactor ph ...
was also named after him.


References


External links


"Josef Stefan: His life and legacy in the thermal sciences,"
''Experimental Thermal and Fluid Science'', Volume 31, Issue 7, July 2007,s 795–803, by John C. Crepeau *
Extended biography of Josef Stefan
by John C. Crepeau {{DEFAULTSORT:Stefan, Josef 1835 births 1893 deaths Slovenian physicists Austrian physicists Austrian male poets Slovenian poets Slovenian male poets Carinthian Slovenes Fluid dynamicists Scientists from Klagenfurt Slovene Austro-Hungarians 19th-century Austrian poets Austro-Hungarian mathematicians 19th-century male writers Rectors of universities in Austria