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Gustav Robert Kirchhoff (Born: 12 March 1824 in Königsberg, East Prussia (now Kaliningrad, Russia) Died: 17 Oct 1887 in Berlin, Germany) was a student of Gauss. He taught at Berlin (an unpaid post) from 1847, then at Breslau. In 1854 he was appointed professor of physics at Heidelberg where he collaborated with Bunsen.

He was a physicist who made important contributions to the theory of circuits using topology and to elasticity. Kirchhoff's Laws, announced in 1854, allow calculation of currents, voltages and resistances of electrical circuits extending the work of Ohm. His work on black body radiation was fundamental in the development of quantum theory.

His work on spectrum analysis led on to a study of the composition of light from the Sun. Kirchhoff was the first to explain the dark lines in the Sun's spectrum as caused by absorbsion of particular wavelengths as the light passes through a gas. This started a new era in astronomy.

In 1875 he was appointed to the chair of mathematical physics at Berlin. Disability meant he had to spend much of his life on crutches or in a wheelchair. His best known work is the four volume masterpiece Vorlesungen über mathematische Physik (1876-94).

Source: http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Kirchoff.html

Gustav Robert Kirchhoff (b. March 12, 1824, Königsberg, Prussia [ now Kaliningrad, Russia ] d. Oct. 17, 1887, Berlin, Ger.), German physicist who, with the chemist Robert Bunsen, firmly established the theory of spectrum analysis (a technique for chemical analysis by analyzing the light emitted by a heated material), which Kirchhoff applied to determine the composition of the Sun.

In 1845 Kirchhoff first announced Kirchhoff's laws, which allow calculation of the currents, voltages, and resistances of electrical networks. Extending the theory of the German physicist Georg Simon Ohm, he generalized the equations describing current flow to the case of electrical conductors in three dimensions. In further studies he demonstrated that current flows through a conductor at the speed of light.

In 1847 Kirchhoff became Privatdozent (unsalaried lecturer) at the University of Berlin and three years later accepted the post of extraordinary professor of physics at the University of Breslau. In 1854 he was appointed professor of physics at the University of Heidelberg, where he joined forces with Bunsen and founded spectrum analysis.

They demonstrated that every element gives off a characteristic coloured light when heated to incandescence. This light, when separated by a prism, has a pattern of individual wavelengths specific for each element. Applying this new research tool, they discovered two new elements, cesium (1860) and rubidium (1861).

Kirchhoff went further to apply spectrum analysis to study the composition of the Sun. He found that when light passes through a gas, the gas absorbs those wavelengths that it would emit if heated. He used this principle to explain the numerous dark lines (Fraunhofer lines) in the Sun's spectrum. That discovery marked the beginning of a new era in astronomy.

In 1875 Kirchhoff was appointed to the chair of mathematical physics at the University of Berlin. Most notable of his published works are Vorlesungen über mathematische Physik (4 vol., 1876-94; "Lectures on Mathematical Physics") and Gesammelte Abhandlungen (1882; supplement, 1891; "Collected Essays").

Source: Britannica Online

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