Lummer, Otto Richard

(b. Gera, Germany, 17 July 1860; d. Breslau, Germany [now Wroclaw, Poland], 5 July 1925)

optics.

After completing his dissertation in 1884, Lummer became an assistant to Helmholtz; and in 1887 he followed the latter to the newly founded Physikalisch Technische Reichsanstalt (PTR) in Berlin. Helmholtz, revered teacher and his constani model, was for Lummer, as Gehrcke recalled, the “absolute standard as a research worker and as a man.” In 1889 Lummer became a member of the PTR, and in 1894 he was given the title of professor. Lummer did not qualify for lecturing until 1901, at the University of Berlin.

As early as 1849 Haidinger had announced the existence of interference fringes that occur on mica plates and that, unlike Newton’s rings, “do not move when the plates producing them are displaced.” These fringes of equal inclination, caused by interference between rays emerging after multiple internal reflections from a parallel-sided plate, were rediscovered (for the third time, after Haidinger and Mascart) by Lummer in 1884 in Helmholtz’ laboratory at the University of Berlin; they became known as Lummer fringes. Helmholtz, who had not perceived the phenomenon because of his nearsightedness, was not willing to accept the existence of the interference effects. He was soon convinced, however, and called Lummer’s dissertation “an unusually good work.”

Since Lummer fringes are the result of differences in path length of many wavelengths, Lummer arrived at the idea, in 1901, of developing the plane parallel plates into a spectroscope of the highest resolution. This device had the advantage of possessing greater resolving power than the interferometer produced in 1897 by Fabry and Perot. The considerable drawback of low luminous intensity, caused by the glancing incidence of the light, was eliminated in 1902 by Gehrcke, who cemented a prism to the plate with Canada balsam. The new apparatus, for which Lummer proposed the name Lummer-Gehrcke interference spectroscope, proved to be an excellent tool for spectroscopy and superior to the simple line grating.

At the PTR, Lummer had the task of working out the bases for a suitable international primary standard of luminosity. In 1889 he constructed, with Brodhun, an exact photometer, the Lummer-Brodhun cube. The new instrument fulfilled “through optical arrangements all the conditions of an ideal grease spot,” something that the previously employed real grease-spot photometer could not do. In photometry it became necessary to hold constant the light sources that were being compared. The existing bolometer was not exact enough for Lu miner’s needs. In 1892, with F. Kurlbaum, he constructed a surface bolometer, which superseded all the previous types. Lummer thus gradually approached the field in which he was to have his greatest successes: thermal radiation.

In 1898, after preliminary work concerning, among other things, the production of the blackbody, Lummer tackled the problem of determining the Kirehhoff function depending only on wavelength and temperature—that is, he was seeking the emissive power of the blackbody. With Pringsheim he confirmed Wien’s displacement law and also, with greater precision, Wien’s radiation law, which Wien had stated in 1896 and Paschen had experimentally ascertained. In 1900, however, Lummer and Pringsheim discovered the “nonvalidity” of this law, which they called the Wien-Planek spectral equation: It “is thereby demonstrated that the Wien-Planck spectral equation does not yield the blackbody radiation that we measured in the region of 12μ to 18μ.”

The competing team of Rubens and Kurlbaum verified this important result and derived from their measurements a conclusion that went even further: “The intensity of a monochromatic beam at high temperatures is proportional to the temperature.” This was the decisive stimulus leading to Planck’s radiation formula, which he communicated on 19 October 1900. Lummer and Pringsheim subsequently confirmed this law with great precision, thereby establishing an unassailable foundation for the emerging quantum theory.

In 1904 Lummer was appointed a full professor at the University of Breslau. At first it was not easy for this specialist in optics to cover the whole field of physics. But his lectures soon became, as Clemens Schaefer wrote, “revelations of a mind in which the divine spark glowed.”

BIBLIOGRAPHY

I. Original Works. Lummer’s writings include “Über eine neue Interferenzerscheinung an planparallelen Glasplatten and eine Methode, die Plan paralleliātat solcher Gläser zu prüfen (Inauguraldissertation),“in Annakn der Physik und Chemie, n.s, 23 (1884), 49-84; “Über eine neue Instrumentenkunde,” ibid., 513-548; “Photometrische Untersuchungen,” in Zeitschrift für Instrumentetikimde, 9 (1889), 41-50, 461-465; 10 (1890), 119-133; 12 (1892), 41-50, written with Eugen Brodhun; “Über die Herstellung eines FlöchenboIometers,” ibid,, 12 (1892), 81-89; “Über die Strahlung des absolut selwarzen Körpers und seine Verwirklichung,“in Naturwissenschaftliche Rundschau, 11 (1896), 65-68, 81-83, 93-95; “Die Vertheilung der Energie im Spectrum des schwarzen Körpers,” in Verhandlungen der Deutsche Physikalischen Geselhchaft, 1 (1899), 23-41, written with Ernst Pringsheim; “Le rayonnement des corps noirs,” in Rapports présentös au Congrös international de physique röuni à Paris en 1900, II (Paris, 1900), 41-99; Die Lehre von der strahlenden Energie (Optik) II, pt. 3 of Müllcr-Pouillet’s Lehrbuch der Physik und Meteorologie 10th ed. (Brunswick, 1909); and Grundlagenf Ziele und Grenzen der Leuehtiechnik (Munich, 1918).

II. Secondary Literature. See Ernst Gehrcke, “Erinnerungen an Lummer,” in Physikalische Blätter, 11 (1955), 315-317; Hans Kangro, Vorgeschichte des Planckschen Stralungsgesetzes (Wiesbaden, 1970), esp. pp. 192-200; Fritz Reiche, “Otto Lummer,” in Physikalische Zeitschrift, 27 (1926), 459-467; and Clemens Schaefer,“Otto Lummer zum 100. Geburtstag,” in Physikalische Blätter, 16 (1960), 373-381.

Armin Hermann