SCHMIDT, GERHARD CARL NATHANIEL

(b. London, England, 5 July 1865; d. Münster, Germany, 16 October 1949) physical chemistry.

Although born in England, Schmidt was of German ancestry. From 1886 he obtained his higher education at Tübingen, Berlin. Strasbourg, Greifswald, and Basel. In 1891, under Georg Kahlbaum’s guidance, he received the Ph.D. at Basel. Schmidt’s subsequent work on solutions, mixtures, and adsorption led to a lifelong interest in physical chemistry. In 1895 he received a Dozentur in Eilhard Wiedemann’s small but exceptionally lively institute at the University of Erlangen. Schmidt often worked closely with Wiedemann himself; he studied luminescence, phosphorescence, and photoelectric phenomena. During a brief excursion into another area in late 1897 or early 1898, he made the discovery for which he is most famous—the radioactivity of thorium. (Marie Curie soon made the same discovery independently.)

Schmidt made this discovery while examining “many elements and compounds” in an effort to determine whether any of the rays that were emitted bore a resemblance to those that Henri Becquerel had found emerging from uranium and uranium compounds. He located only one such element, thorium, and immediately conducted absorption, ionization, reflection, refraction, and polarization studies to determine the characteristics of its rays. Having combined a misinterpretation of Becquerel’s with one of his own, Schmidt concluded that thorium rays most resembled Röntgen rays—a conclusion that soon required revision in view of the researches of Marie Curie and Ernest Rutherford.

In 1900 Schmidt became professor ordinarius of physics at the Forstakademie in Eberswalde but soon moved to Erlangen as professor extraordinarius (1901–1904). He then went to Königsberg as professor ordinarius and director of the physical institute (1904–1908) and finally to Münster, where he occupied the chair once held by Hittorf, whom Schmidt admired and commemorated in several addresses. Schmidt retired from this post in 1935.

During these years, Schmidt studied canal-ray and cathode-ray phenomena, the electrical conductivity of salt vapors, solid electrolytes, adsorption, passivity, and luminescence. He was unusually vigorous and healthy until the last year of his life, when he fractured his hipbone and was hospitalized. Shortly after he was released, he suffered a stroke and died.

BIBLIOGRAPHY

I. Original Works. Schmidt’s writings include “Ueber die von den Thorverbindungen und einigen anderen Substanzen ausgehende Strahlung,” in Annalen der Physik, 65 (1898), 141–151; “Wilhelm Hittorf,” Schriften der Gesellschaft zur Förderung der West-fälischen Wilhelms-Universität zu Münster, no. 4 (1924); and “Eilhard Wiedemann,” in Physikalische Zeistschrift,29 (1928), 185–190.

II. Secondary Literature. On Schmidt and his work, see Lawrence Badash, “The Discovery of Thorium’s Radioactivity,” in Journal of Chemical Education, 43 (1966), 219–220. For obituary notices see A. Kratzer, Physikalische Blätter,6 (1950), 30; and K. Kuhn, Naturwissenschaftliche Rundschau, 4 (1951). 41. Schmidt’ portrait is in J. A. Barthm Deutsche Senioren der Physik (Leipzig, 1936).

Roger H. Stuewer