Hallwachs, Wilhelm Ludwig Franz

(b. Darmstadt Germany, 9 July 1859;) d. Dresden, Germany, 20 June 1922)

physics.

Hallwachs was one of the pioneers of modern physics. An experimental physicist, he laid the foundations for research on photoelectric processes. He received his education at the universities of Strasbourg and Berlin, earning his doctorate in 1883 under A. A. Kundt at Strasbourg. He was then an assistant to Friedrich Kohlrausch at Würzburg from 1884 to 1886 and, from 1886 to 1888, to G. H. Wiedemann at Leipzig, where he qualified as lecturer in 1886. In 1888 he again became an assistant to Kohlrausch, this time at Strasbourg, and married the latter’s daughter Marie in 1890. He became professor of electrical engineering in 1893 and of physics in 1900 at the Technische Hochschule in Dresden. During his teaching career he introduced and fostered the study of engineering physics.

Hallwachs constructed electrical measuring devices and built, among other things, a quadrant electrometer and a double refractometer of high precision. At Leipzig in 1888 he investigated, following the model of Heinrich Hertz’s studies, photoelectric activity, establishing that through absorption of ultraviolet light, negatively charged metal plates discharge and uncharged metal plates become positively charged. This process, which is called the photoelectric effect or Hallwachs effect, forms the basis for the physics of the photoelectric cell and was theoretically interpreted in 1905 in Einstein’s work on light quanta.

Hallwachs interrupted his photoelectric investigations and, beginning in 1890, worked with Kohlrausch on electrolytic questions. After 1904, when he was able to return to photoelectricity, he determined the value of the photoelectric work function, photoelectric fatigue, and related phenomena. He became the leading expert in this field, summarizing its development to 1914 in his treatise “Die Lichtelektrizität.”

BIBLIOGRAPHY

I. Original Works. A bibliography is in Poggendorff, IV, 572, and V, 489, and in Wiener’s obituary (see below). Hallwachs wrote about 50 scientific papers. The most important are “Ueber den Einfluss des Lichtes auf electrostatisch geladene Körper,” in Annalen der Physik und Chemie, n.s. 33 (1888), 301–312; “Ueber die Electrisierung von Metallplatten durch Bestrahlung mit electrischem Licht,” ibid., n.s. 34 (1888), 731–734; “Ueber den Zusammenhang des Electricitätsverlustes durch Beleuchtung mit der Lichtabsorption,” ibid., n.s. 37 (1889), 666–675; and “Die Lichtelektrizität,” in Erich Marx, ed., Handbuch der Radiologie, III (Leipzig, 1916), 245–563. Hallwachs was the coeditor, with A. Heydweiller, K. Strecker, and O. Wiener, of F. Kohlrausch, Gesammelte Abhandlungen, 2 vols. (Leipzig, 1910–1911).

II. Secondary Literature. The main biography is O. Wiener, “Wilhelm Hallwachs,” in Berichte über die Verhandlungen der Sächsischen Akademie der Wissenschaften zu Leipzig, Math.-phys. Kl., 74 (1922), 293–316, with bibliography on 313–316; abridged version in Physikalische Zeitschrift, 23 (1922), 457–462. See also A. Hermann, in Neue deutsche Biographie, VII (l966), 565–566. For information on Hallwachs’ work, see Erich Marx, “Anhang: Entwicklung der Lichtelektrizität von Januar 1914 bis Oktober 1915,” in Marx’s work cited above.

Hans-GÜnther KÖrber