(b. Stuttgart, Germany, 1 December 1845; d. Göttingen, Germany, 11 June 1915)
Riecke received his early education in Stuttgart and in 1866 entered the University of Tübingen to study mathematics under Carl Neumann, son of Franz Neumann, the great theoretician. He also studied experimental physics with E. Reusch, who whetted his interest in theoretical studies in crystal physics. This combination of experimental and theoretical work was to be a hallmark of Riecke’s later work. He completed his undergraduate studies in 1869 and took a teaching post in mathematics at a school in Stuttgart.
At the beginning of 1870 Riecke was offered a state scholarship to continue his studies at the University of Göttingen. He had hardly begun this work when he was conscripted to serve in the Franco-Prussian War. The following year he returned to Göttingen to study mathematics with Clebsch and experimental physics with W. Weber and Kohlrausch. In May 1871, under Weber’s guidance, he completed his dissertation on the magnetization numbers of iron in weak magnetic fields.
In 1873 Riecke was called to Göttingen as extraordinary professor of physics; and in 1881 he became ordinary professor, taking over Weber’s laboratory and institute. When W. Voigt was named ordinary professor of theoretical physics (1883) at Göttingen, he and Riecke were promised a new physics institute. Although this institute did not actually begin functioning until 1905, Riecke carried out, under difficult conditions, both experimental and theoretical studies over a wide range of areas in physics and physical chemistry during his forty-five-year tenure at Göttingen. His competence in physics is reflected in his textbook. Lehrbuch der Physik (1896), which went through five editions. In 1899 Riecke became the first editor of the journal Physikalische Zeitschrift; he continued his close association with the journal until his death, Even at the age of seventy he remained an active worker in physics. His last work, published posthumously in June 1915, was a rigorous mathematical résumé of particle physics and line spectra in which he concentrated on Bohr’s theory of series spectra in hydrogen and helium.
Early in his career Riecke studied ferromagnetism and showed (1871) that in the presence of weak magnetic fields the magnetization numbers for iron are not independent of the strength of the external field, as had been assumed by Franz Neumann. About 1885 Riecke conducted theoretical and experimental researches in hydrodynamics and later, about 1890, undertook theoretical studies in thermodynamics, concentrating on the concept of thermodynamic potentials, which he applied to problems in physical chemistry. Noteworthy among these studies was one, in 1893. in which he analyzed muscle contraction in living organisms by using thermodynamic potentials.
The chief thrust of Riecke’s research was related to the revival and establishment of granular theories of electricity and crystal structure. The particulate nature of electricity had been proposed by Weber but had been under severe attack during the 1860’s and 1870’s. It was largely through the efforts of Helmholtz that the granular theory of electricity was revived in the 1880’s. Helmholtz had stressed the fact that if one accepts the hypothesis that matter is atomistic, then one must also accept an atomistic conception of electricity, Riecke sought to confirm this atomic hypothesis of electricity: with the aid of (1) Geissler tubes, (2) studies of atmospheric electricity and the motion of electrified particles in the electromagnetic field. (3) mathematical and experimental studies on the behavior of crystals, and (4) researches in the metallic state and electrical conduction in metals. His researches in these areas were not done serially but were intertwined, stretching over the period 1880–1915.
The most noteworthy of his results in Geissler tubes was the identification of negatively charged particles projected from the cathode; and he demonstrated that this charge is the same regardless of the metal from which the cathode is constructed (1899), Riecke’s analysis of the motion of electrified particles in electromagnetic fields (1902) had direct application to the theory of the aurora. Also, he made important contributions to the molecular theory of pyroelectric and piezoelectric phenomena in tourmaline and quartz (1891, 1914). But his most important and influential researches were undoubtedly on the theory of conduction in metals and a granular theory of the properties of metals.
Riecke’s major paper on this subject was published in 1898. He envisaged the metal as being composed of neutral atoms bound together in a lattice. Provision was made for ionization of some of these atoms to explain positive metal ions and negative electrons. The properties of the metal were accounted for by hypothesizing relationships between the two types of charged particles and their environment. The theory attempted to analyze electrical conduction; heat conduction; the Wiedemann-Franz ratio; various contact effects (including the Peltier effect, contact potentials, and the Thompson effect); various phenomena associated with the presence of an external magnetic field (including the Hall effect, the Nernst effect, and the Ledue effect); and electrical and thermal conductivity in alloys.
Riecke’s basic assumption was that the space between molecules contained not only negative but also positive particles. Each metal molecule was capable of discharging both positive and negative charges by collision. The discharged ions then drifted in straight lines until they came under the influence of metal molecules still bound in the lattice, under the influence of which the ions were bent into circular paths of various sizes. Thus the charges would move randomly through the metal. The model was that of a gas; and Riecke assumed that the average speed of the particles was proportional to the square root of the absolute temperature, thus making it possible to apply the mathematical techniques of the kinetic theory of gases to the properties of metals.
The chief success of the theory, the accurate prediction of the Wiedemann-Franz ratio, was shortlived since soon after Riecke produced his theory it was shown that the ratio of the thermal conductivity to the electrical conductivity for most metals is not strictly proportional to the temperature. Nevertheless, Riecke had broken new ground. Drude and Lorentz followed with more successful variants of the Riecke theory, which themselves were eventually supplanted in 1927 and 1928 by the Sommerfeld theory utilizing nonclassical, Fermi-Dirac statistics.
I. Original Works. Many of Riecke’s papers were published in both the Göttingen Nachrichten and the Annalen der Physik. Where such duplication exists the more easily accessible Annalen der Physik has been cited. His papers include “Ueber die elektrischen Elementargesetze,” in Annalen der Physik, 11 (1880), 278–315; “Ueber die sogenannte unipolare Induction,” Ibid., 413–432; “Ueber die Bewegung eines elektrischen Teilchens in einem homogenen magnetischen Felde und das negative elektrische Glimmlicht,” Ibid., 13 (1881), 191–194; “Messung der vom Erdmagnetismus auf einen drehbaren linearen Stromleiter ausgeübten Kraft,” Ibid., 194–204; “Beiträge zur Lehre vom inducirten Magnetismus,” Ibid., 465–507; “Ueber die elektromagnetische Rotation einer Flüssigkeit,” Ibid., 25 (1885), 496–511; and “Ueber die Pyroelektricität des Turmalins,” Ibid., 28 (1886), 43–80; and 40 (1890), 264–306.
Subsequent writings are “Ueber elektrische Ladung durch gleitende Reibung,” Ibid., 42 (1891), 465–482; “Das thermische Potential für verdbrinten Lösungen,” Ibid., 483–501; “Thermodynamik des Turmalins und mechanische Theorie der Muskelcontraction,” 49 (1893), 430–458; “Moleculartheorie der piëzoelectrischen und pyroelectrischen Erscheinungen,” Ibid., 459–486; “Der Satz vom thermodynamischen Potential beim Gleichgewichte eines heterogenen Systems mit Anwendung auf die Theorie von van der Waals und das Gesetz des Siedepunktes,” 53 (1894), 379–391; “Zur Lehre von der Quellung,” Ibid., 564–592; “Ueber die Vertheilung der freien Elektricität in Innern einer Geissler’schen Röhre,” Ibid., 63 (1897), 220–233; “Zur Theorie des Galvanismus and der Wärme,” 66 (1898), 353–389, 545–581; “Ueber den Reactionsdruck der Kathodenstrahlen,” Ibid., 954–979; and “Ueber die Vertheilung von freier Elektricität an der Oberfläche einer Crooks’schen Röhre,” Ibid., 69 (1899), 788–800.
Later writings include “Zur Kinetik der Serienschwingungen eines Linienspektruns,” Ibid., 1 (1900), 399–413; “Ueber das Verhältnis der Leitfähigkeiten der Metalle für Wärme and für Elektricität,” Ibid., 2 (1900), 835–842; “Ueber charakteristische Curven bei der elektrischen Entladung durch verdünnte Gase,” Ibid., 4 (1901), 592–616; “Ist die metallische Leitung verbunden mit einem Transport von Metallionen?” in Physikalische Zeitschrift, 2 (1901), 639; “Ueber die Zerstreuung der Electricitat in abgeschlossenen Räumen,” in Göttingen Nachrichten (1903), 1–16, 32–38; “Ueber näherungweise gestättige Ströme zwischen plan-parallelen Platten,” Ibid., 336–343; “Ueber einige Eigenschaftcn des Radiumatoms,” ibid. (1907), 163–170; “Ueber die Bewegung der α-Ionen,” in Annalen der Physik, 27 (1908), 797–818; “Zur Theorie des Interferenzversuches von Michelson,” in Göttingen Nachrichten (1911), 271–277; “Zur molekularen Theorie der Piezoelektrizität des Turmalins,” in Physikalische Zeitschrift, 13 (1912), 409–415; and “Bohrs Theorie der Serienspektren von Wasserstoff and Helium,” Ibid., 16 (1915), 222–227.
II. Secondary Literature. E. T. Whittaker, A History of the Theories of Aether and Electricity, 2 vols. (New York, 1960), esp. I, chap. 11. An obituary notice by W. Voigt appears in Physikalische Zeitschrift, 16 (1915), 219–221.