Kirchhoff, Gustav Robert

Kirchhoff, Gustav Robert (gs`täf rō`bĕrt kĭrkh`hôf), 1824–87, German physicist. He served as professor of physics at the universities of Breslau (1850–54), Heidelberg (1854–74), and Berlin (from 1875). He is known especially for his work with the spectroscope in association with R. W. Bunsen, with whom he discovered the elements cesium and rubidium, and for his explanation of the Fraunhofer lines in the solar spectrum. He also did important research in electricity (he formulated Kirchhoff's laws) and thermodynamics.

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Kirchhoff, Gustav Robert

(born March 12, 1824, Königsberg, Prussia—died Oct. 17, 1887, Berlin, Ger.) German physicist. Kirchhoff's laws (1845) allow calculation of the currents, voltages, and resistances of electrical networks (he was the first to show that current flows through a conductor at the speed of light) and generalized the equations describing current flow to three dimensions. With Robert Bunsen, he demonstrated that every element emits coloured light when heated at wavelengths specific to it, a fact that is the basis of spectrum analysis. They used this new research tool to discover cesium (1860) and rubidium (1861), and began a new era in astronomy when they applied it to the spectrum of the sun.

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Kirchhoff, Gustav Robert 

Born Mar. 12, 1824, in Königsberg; died Oct. 17, 1887, in Berlin. German physicist. Member of the Berlin Academy of Sciences (1874) and corresponding member of the St. Petersburg Academy of Sciences (1862).

Kirchhoff graduated from the University of Königsberg in 1846. He was a professor at the universities of Breslau (1850) and Heidelberg (1854). In 1875 he was appointed to the chair of mathematical physics at the University of Berlin.

Kirchhoff’s scientific works were devoted to optics, electrodynamics, mechanics, and other areas. In 1847 he solved the problem of the distribution of currents in electric networks (seeKIRCHHOFF’S LAWS). He had also done research in discharge of capacitors and induction of currents. In mechanics he was primarily concerned with questions of deformation, equilibrium, motion of elastic bodies, and fluid flow. His Vorlesungen über matematische Physik (Lectures on Mathematical Physics, 1874–94) played an important role in the development of theoretical physics.

In 1854 Kirchhoff and R. W. Bunsen began studying the spectra of flames colored by vapors of metallic salts. As a result, they created the foundations for spectrum analysis, which, after the completion of their work (1859–61), was introduced into practice in chemical investigations. With the aid of this new method they discovered cesium (1860) and rubidium (1861). In 1859, Kirchhoff formulated one of the basic laws of thermal radiation (seeKIRCHHOFF’S RADIATION LAW) and introduced the concept of a black body into physics. In 1860 he discovered the rule for reversal of spectral lines and was the first to explain correctly the dark lines of the solar spectrum (Fraunhofer lines), proposing the probable chemical composition of the solar atmosphere.

WORKS

Vorlesungen über mathematische Physik, vols. 1–4. Leipzig, 1874–94.
Gesammelte Abhardlungen. Leipzig, 1882.
Untersuchungen über das Sonnenspektrum und die Spektren der chemischen Elemente. Berlin, 1861–62.

REFERENCES

Stoletov, A. G. Gustav Robert Kirkhgof, sobr. soch., vol. 2. Moscow-Leningrad, 1841.
Gornshtein, T. N. “Kirkhgof i ego issledovaniia no teplovomu izlucheniiu.” Tr. In-ta istorii estestvoznaniia i tekniki, 1960, issue 34, pp. 110–56.
Agassi, J. “The Kirchhoff-Planck Radiation Law.” Science, 1967, vol. 156, no. 3771, pp. 30–37.