Hankel, Wilhelm Gottlieb

(b. Ermsleben, Harz, Germany, 17 May 1814; d. Leipzig, Germany, 17 February 1899)

physics, chemistry.

Hankel belongs among the older nineteenth-century physicists who typically represented the classical scientist. The son of a choirmaster and teacher, he was greatly interested in practical questions even as a child. After graduating from the Gymnasium at Quedlinburg, he studied at the University of Halle under Johann Schweigger. In 1835 he was an assistant in the physics laboratory and, in 1836, a teacher at the newly founded Realschule of the Frankische Stiftung in Halle. In 1838 he married the daughter of a farmer from near Halberstadt; in 1839 they had a son, Hermann, who became famous as a mathematician. Also in 1839 Hankel earned his doctorate with a dissertation on the electricity of crystals, and in 1840 he qualified to lecture in chemistry at the University of Halle.

In 1842–1843 a severe case of pleurisy forced Hankel to give up his work in the chemistry laboratory, and he turned his attention completely to physics, a decision that he had not made previously out of respect for his teacher Schweigger. In 1847 he obtained a professorship in physics at the University of Halle and, in 1849, a similar position at the University of Leipzig, which he held until 1887.

As an experimenter Hankel investigated primarily piezoelectric and thermoelectric phenomena in crystals and became a pioneer in this specialized field. His thorough observations and measurements were based on the use of new, more reliable measuring instruments which he himself constructed or improved. In 1850 he developed a new electrometer of high sensitivity and low self—capacity, which was utilized in conjunction with a microscope. In his researches Hankel discovered the relationship in crystals between pyroelectric properties and the rotation of the plane of polarization of light. He drew attention to crystal structure and to crystals with and without inversion centers, thereby clarifying the peculiarities of their electrical properties. Moreover, he investigated the thermoelectric currents between metals and minerals as well as the photoelectricity of fluorite and the actinoelectricity of quartz. In addition, Hankel carried out more precise determinations of the galvanic electromotive series. He also studied electricity in flames and gas formation. He reduced his observations on atmospheric electricity, through the use of a torsion balance, to values of the system of absolute measurement by an experimental method (comparison of a known electrostatic field with the atmospheric electrical field) which was complicated but quite exact for the period (1858). In 1856 he wrote a thorough critique of the instruments used until then in studying atmospheric electricity.

Hankel proposed a new theory of electricity which postulated, instead of action at a distance, the existence of variously oriented rotational motions in a single fluid: ether. The theory excited little enthusiasm when it was announced and now merits only historical interest as one in a series of ultimately fruitless efforts to reduce electrodynamics to mechanics.

BIBLIOGRAPHY

I. Original Works. Hankel wrote sixty-two scientific papers, most of them published in Berchte über die Verhandlungen der K. Sächsisehen Gesellschaft der Wissenschaften zu Leipzig and in Annalen der Physik und Chemie. About twenty-five dealt with the pyroelectricity of crystals. A bibliography may be found in Poggendorff, I, 1011; III, 581–582 and IV, 580.

His scientific papers include “De thermo-electricitate crystallorum” (Halle, 1839), his doctoral dissertation, extracts from which were published as “Ueber die Thermo-Elektricität der Krystalle,” in Annalen der Physik und Chemie, 49 (1840), 493–504, and 50 (1840), 237–250; and as “Nachtrag zu der Thermo-Elektricität des Topases,” ibid., 56 (1842), 37–58; “Ueber die Construction eines Elektrometers,” ibid., 84 (1851), 28–36; “Ueber die Messung der atmosphärischen Elektricität nach absolutem Maasse,” ibid., 103 (1858), 209–240; “Maassbestimmungen der elektromotorischen Kräfte,” ibid., 115 (1862), 57–62, and 126 (1865), 286–298; “Neue Theorie der elektrischen Erscheinungen,” ibid., 126 (1865), 440–466, and 131 (1867), 607–621; “Ueber die thermoelektrischen Eigenschaften des Bergkrystalle,” ibid., 131 (1867), 621–631; “Ueber einen Apparat zur Messung sehr kleiner Zeiträume: ibid., 132 (1867), 134–165; “Ueber die actino- und piezoelectrischen Eigenschaften des Bergkrysialles und ihre Beziehungen zu den thermoelectrisehen,” ibid., n.s. 17 (1882), 163–175; “Neue Beobachtungen über die Thermo- und Actinoelektricität des Bergkrystalles…” ibid., 19 (1883), 818–844; “Endgültige Feststellung der auf den Bergkrystallen an den Enden der Nebenaxen bei steigenden und sinkenden Temperaturen auftretenden Polaritäten,” ibid., 32 (1887), 91–108; “Das elektrodynamische Gesetz ein Punktgesetz,” ibid., 36 (1889), 73–93; and “Die galvanische Kette,” ibid., 39 (1890), 369–389.

Hankel’s books include Grundriss der Physik (Halle, 1848). He also translated into German D. F. J. Arago’s Notices biographiques, 3 vols. (Leipzig, 1856), and his Astronomie populaire, 2nd ed., 4 vols, (Leipzig, 1865). In addition, he edited Arago’s Sämmtliche Werke, 16 vols. (Leipzig, 1854–1860).

II. Secondary Literature. See C. Neumann, “Worte zum Gedächtnis an Wilhelm Hankel” in Berichte über die Verhandlungen der K. Sächsischen Gesellschaft der Wissenschaften zu Leipzig. Math.-phys. Kl., 51 (1899), Ixii-lxvi; and P. Drude. “Wilhelm Gottlieb Hankel,” ibid., Ixvii–lxxvi.

Hans-GÜnther KÖrber