Rudolf Hermann Arndt Kohlrausch (November 6, 1809 in

Göttingen Göttingen (, , ; nds, Chöttingen) is a university city in Lower Saxony, central Germany, the capital of the eponymous district. The River Leine runs through it. At the end of 2019, the population was 118,911. General information The ori ...

– March 8, 1858 in

Erlangen Erlangen (; East Franconian: ''Erlang'', Bavarian: ''Erlanga'') is a Middle Franconian city in Bavaria, Germany. It is the seat of the administrative district Erlangen-Höchstadt (former administrative district Erlangen), and with 116,062 inha ...

) was a German

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 cau ...

Biography

He was a native of

, the son of the Royal Hanovarian director general of schools Friedrich Kohlrausch. He was a high-school teacher of mathematics and physics successively at

Lüneburg Lüneburg (officially the ''Hanseatic City of Lüneburg'', German: ''Hansestadt Lüneburg'', , Low German ''Lümborg'', Latin ''Luneburgum'' or ''Lunaburgum'', Old High German ''Luneburc'', Old Saxon ''Hliuni'', Polabian ''Glain''), also called ...

, Rinteln,

Kassel Kassel (; in Germany, spelled Cassel until 1926) is a city on the Fulda River in northern Hesse, Germany. It is the administrative seat of the Regierungsbezirk Kassel and the district of the same name and had 201,048 inhabitants in December 2020 ...

and

Marburg Marburg ( or ) is a university town in the German federal state (''Bundesland'') of Hesse, capital of the Marburg-Biedenkopf district (''Landkreis''). The town area spreads along the valley of the river Lahn and has a population of approximat ...

. In 1853 he became an associate professor at the

University of Marburg The Philipps University of Marburg (german: Philipps-Universität Marburg) was founded in 1527 by Philip I, Landgrave of Hesse, which makes it one of Germany's oldest universities and the oldest still operating Protestant university in the wor ...

, and four years later, a full professor of physics at the

University of Erlangen A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. Universities typically offer both undergraduate and postgraduate programs. In the United States, th ...

Research

In 1854 Kohlrausch introduced the relaxation phenomena, and used the

stretched exponential function The stretched exponential function f_\beta (t) = e^ is obtained by inserting a fractional power law into the exponential function. In most applications, it is meaningful only for arguments between 0 and +∞. With , the usual exponential function ...

to explain relaxation effects of a discharging

Leyden jar A Leyden jar (or Leiden jar, or archaically, sometimes Kleistian jar) is an electrical component that stores a high-voltage electric charge (from an external source) between electrical conductors on the inside and outside of a glass jar. It ty ...

(capacitor). In 1856, with Wilhelm Weber (1804–1891), he demonstrated that the ratio of

electrostatic Electrostatics is a branch of physics that studies electric charges at rest ( static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for ...

to electromagnetic units produced a number that matched the value of the then known

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit fo ...

. This finding was instrumental towards Maxwell's conjecture that

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 t ...

is an

electromagnetic wave In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) ...

. Also, the first usage of the letter "c" to denote the speed of light was published in an 1856 paper by Kohlrausch and Weber.

Family

He was the father of physicist Friedrich Kohlrausch.

Published works

* ''Elektrodynamische Maaßbestimmungen : insbesondere Zurückführung der Stromintensitäts-Messungen auf mechanisches Maass'' (with Wilhelm Weber) 1857.OCLC
Elektrodynamische Maaßbestimmungen

Notes

References

"The evolution of applied harmonic analysis"
by Elena Prestini
PhysicsWorld
"Blast from the Past" *

External links

* 1858 deaths 1809 births Scientists from Göttingen 19th-century German physicists University of Erlangen-Nuremberg faculty University of Marburg faculty {{Germany-scientist-stub