Kirchhoff
NAME: Kirchhoff, Gustav Robert
ACHIEVEMENT(S): Spectroscopy
NICKNAME/ALIAS: None
DATE/PLACE OF BIRTH: 12 March 1824, at Königsberg, Prussia, Germany
DATE/PLACE/AGE AT DEATH: 17 October 1887, in Berlin, Germany. Aged 63
DISCIPLINE: Physicist
FIELD: Physics
LANGUAGE: German
PARENTS: ?
SIBLINGS: ?
SPOUSE: Clara Richelot (d. 1869), married 1847; Luise Brommel, married 1872
CHILDREN: Two sons and two daughters from first marriage
EDUCATION: University of Konigsberg, to 1847
MAJOR WORK: 'Lectures on Mathematical Physics', 1876-94
LIFE AND TIMES: While still a university student, Kirchhoff made his first important contribution to physics (on the conduction of electricity) when in 1845-47 he extended <extended law of> Ohm's* Law [which states that the current flow through an electrical conductor is directly proportional to the potential difference (voltage), and inversely proportional to the resistance] to the cases of closed circuits and of electrical conductors in a three-dimensional network.
From this generalization, Kirchhoff derived what are now known as ‘Kirchhoff's laws,’ that allow the calculation of the current, voltage or resistance at any point in an electrical network.
In 1850, Kirchhoff was appointed extraordinary professor of physics at the University of Breslau, where the following year he was joined by the chemist <collaborated with> Bunsen*, with whom he formed a lasting friendship.
In 1852, Bunsen moved to the University of Heidelberg, and two years later Kirchhoff followed him there as professor of physics. At Heidelberg Kirchhoff continued his electrical investigations, and in 1857 showed theoretically that an oscillating current is propagated in a conductor of zero resistance at the speed of light. This discovery would prove important for the development in the 1860s of the electromagnetic theory of light by <laid ground for> Maxwell*.
Meanwhile, during the 1850s Bunsen's technician Peter Desdega constructed the first Bunsen burner, with which Bunsen and Kirchhoff began to investigate the distinctive colours that metals and their salts produce in a flame.
It was Kirchhoff who realised that accurate identification could be achieved by using a prism to produce spectra of the coloured flames. As a result, in the late 1850s Bunsen and Kirchhoff collaborated on the development of the <developed> spectroscope*, and in 1860 demonstrated that every element when heated to incandescence gives off a characteristic coloured light which, when separated by a prism, has a pattern of individual wavelengths, or set of spectral lines, specific for each element.
In 1860, Bunsen and Kirchhoff announced the discovery of a fourth metal, cesium, in the series of alkaline earths, and the following year a new metal, rubidium, was discovered by Bunsen. During this period they also made important improvements in the construction of spectroscopes, adding a third tube with a scale and a reflection prism to provide a standard spectrum to compare against an unknown spectrum.
Using a spectroscope employing four prisms, in 1869 Kirchhoff obtained a much broadened solar spectrum in which he was able to identify a large number of terrestrial elements.
During these investigations, in 1859, he noticed that certain dark lines in the Sun's spectrum, which had been seen by <continued work of> Fraunhofer* in 1814, were intensified if the sunlight passed through a sodium flame. (This observation had in fact been made ten years earlier by <anticipated by> Foucault*, but had not been followed up).
Kirchhoff almost immediately came to the correct conclusion that the sodium flame was absorbing light from the sunlight of the same colour that it emitted, and explained that the Fraunhofer lines are due to the absorption of light by sodium and other elements present in the Sun's atmosphere.
Concluding that the dark lines crossing the Sun's spectrum indicate the presence in the Sun's atmosphere of certain elements in the vapor state, he was able to work out that the vapors in the chromosphere (the red gaseous envelope around the Sun, outside the
photosphere) are cooler than the lower photosphere of the Sun and that they absorb their own characteristic wavelengths from the Sun's spectrum according to his newly-discovered law:- that a substance which emits light of a certain wavelength at a given temperature will also absorb light of the same wavelength at that temperature.
He concluded that some of the wavelengths emitted are absorbed by the vapors in the chromosphere as the Sun's light passes through them, producing the dark lines. From this he was able to identify the elements in the Sun's atmosphere fromthe Fraunhofer lines. The technique opened up a whole new era of astronomy.
Kirchhoff continued to develop the theoretical aspects of this work, and in 1859 he announced another important law:- that the ratio of the emission and absorption powers of all material bodies is the same at a given temperature and a given wavelength of radiation produced.
From this, in 1862 Kirchhoff then derived the concept of a perfect black body - one that would absorb and emit radiation at all wavelengths. This work was continued in the1890s by <laid ground for> Pringsheim* and Otto Lummer, and would prove fundamental to the development of quantum theory.
Aside from these achievements, Kirchhoff was also known as an excellent teacher, counting among his students the Russian chemist <taught> Mendeleyev* and the Dutch physicist <taught> Onnes*.
In 1875, Kirchhoff was appointed to the chair of mathematical physics at the University of Berlin. Illness forced him to retire in 1886.
Kirchhoff also made important contributions to theoretical physics, especially in analytical dynamics; in the theory of vibrating plates; in the propagation of sound in tubes; and to the theory of light diffraction.
ASSESSMENT: He was undoubtedly one of the outstanding physicists of the century.
EXTRA CONNECTIONS: Worked with <worked with> Runge*, <worked with> Caro* and <worked with> Liebig*.
Influenced <influenced> Einstein*
<his technique used by> Crookes* used the spectroscope to discover thallium.
Spectroscopy made possible the observation of the <work affected that of> Doppler*-<work affected that of> Fizeau* effect.
He knew <knew> Kuhne*
His work was anticipated by <anticipated by> Plucker*
He taught <taught> Planck*
<his technique used by> Vierordt* and <his technique used by> Winkler* used his technique
ONELINER: GR Kirchhoff, who developed spectroscopy
BIBLIOGRAPHY:
DSB, EB
Dict. Biog of Physicists