The American Cyclopædia (1879)/Kirchhoff, Gustav Robert

KIRCHHOFF, Gustav Robert, a German physicist, born in Königsberg, March 12, 1824. In 1845 he published an essay on the passage of the electric current through planes. He graduated at Königsberg in 1846, and in 1848 began lecturing in Berlin on mathematical physics, and published several elaborate articles on electrology. In 1850 he was appointed lecturer on experimental physics at Breslau, and in 1854 professor of natural philosophy at Heidelberg, which chair he still occupies (1874). Between 1850 and 1858 he published numerous articles on magnetism, electricity, heat, and the tension of vapors; and in 1859 he made the discovery which has rendered him famous, the cause of Fraunhofer's lines in the solar spectrum. Euler a century ago, and in later years Talbot, Miller, Wheatstone, Foucault, Angström, Balfour Stewart, and Tyndall, had all been very close upon the discovery; but Kirchhoff (in Poggendorff's Annalen, vol. cix., p. 275), was the first to propound and demonstrate the law: &ldquo;The relation between the power of emission and the power of absorption of one and the same class of rays is the same for all bodies at the same temperature.&rdquo; This was the basis of his invention in 1860, in conjunction with R. W. Bunsen, of the new method of qualitative chemical analysis called spectrum analysis. (See .) He published Untersuchungen über das Sonnenspectrum und die Spectren der chemischen Elemente, which contains his views of the physical constitution of the sun (Berlin, 1861; 3d ed., 1866); and with Bunsen, Chemische Analyse durch Spectralbeobachtung (Vienna, 1861). He and Bunsen together, by means of spectrum analysis, discovered two new metals, cæsium and rubidium. In 1870 Kirchhoff became a foreign member of the Berlin academy of sciences; and subsequently the Prussian order pour le mérite, the highest honor of its kind in Germany, was conferred upon him. Recently he has begun the publication of what is designed to be an elaborate work on mathematical physics. The first part bears the title, Vorlesungen über analytische Mechanik, mit Einschluss der Hydrodynamik und der Theorie der Elastizität fester Körper (Leipsic, 1874).