Hartmann, Johannes Franz

(b. Erfurt, Germany, 11 January 1865; d. Göttingen, Germany, 13 September 1936)

astronomy.

Hartmann was the son of Daniel Hartmann, a merchant, and Maria Sophia Hucke. He attended primary and secondary school in Erfurt, at which time his interest in astronomy began to develop. He continued his studies at Tübingen, Berlin, and Leipzig, where H. Bruns taught him the mathematics that were basic to his future work. Hartmann took the Ph.D. at Leipzig in 1891, then remained there to participate in making observations for the star catalog of the Astronomische Gesellschaft. He worked at the Leipzig observatory until 1896, interrupted by a period of some months that he spent at the observatory in Vienna.

In 1896 Hartmann went to the astrophysical observatory at Potsdam. He stayed there until 1909, receiving the title of observator in 1898 and of professor in 1902. At Potsdam, Hartmann was chiefly active in the fields of instrumentation and spectrography. The Potsdam observatory possessed a thirtytwo-inch refractor, but the preparation of its objective for use in the new technique of photographic observation had not been successful. Hartmann was assigned to investigate the problem; he derived a new interpolative dispersion formula and with it developed a new method for testing large objectives. This formula was later important in his spectroscopic investigations.

Hartmann’s other important work at Potsdam included the construction of a new spectrograph that employed a quartz prism and the investigation of the ultraviolet frequencies of previously unstudied stellar spectra. He also devised a spectrocomparator to expedite the evaluation of stellar spectra, as well as two photometric instruments, a microphotometer and a plane, or universal, photometer. His most significant work at this time, however, was the discovery of stationary calcium lines in the spectrum of δ Orionis (1904) through observing its radial velocity by the Doppler shift of its spectral lines. He thus proved the existence of interstellar matter for the first time.

Hartmann left Potsdam in 1909 to accept a position as director of the observatory and professor in ordinary at the University of Göttingen. The equipment of the observatory was obsolete and teaching was new to Hartmann; he therefore changed the emphasis of his work to concentrate on lecturing, writing, and the history of astronomy. The government of Argentina offered him the directorship of the La Plata observatory in 1911; he refused that offer, but accepted when it was repeated in 1921.

The observatory at La Plata was better equipped than the one at Göttingen, and Hartmann further improved its instrumentation. Most important, he reconstructed the thirty-two-inch reflector for the spectroscopic work which was urgently needed in southern skies. He also gave lectures in Spanish and made geophysical observations, primarily in the area of seismics. He further made a new determination of the solar parallax from the observations of the opposition of the asteroid Eros in 1931-1932.

In 1935 Hartmann returned to Göttingen, where he planned to spend his retirement evaluating scientific data. His health failed, however, and he died after a long illness. He was married to Maria Scherr; they had two sons and one daughter. He had been an active sportsman, and his interest in music continued until the end of his life.

BIBLIOGRAPHY

I. Original Works. Hartmann’s works include “Apparat und Methode zur photographischen Messung von Flächenhelligkeiten,” in Zeitschrift für Instrumentenkunde, 19 (1899), 97-103; “Interpolationsformeln für das prismatische Spektrum,” in Publikationen des Astrophysikalischen Observatoriums zu Potsdam, 12 (1902); “Das 80-cm. Objektiv des Potsdamer Refraktors,” ibid., 15 (1904); “Messungen der Linienverschiebungen in Spektrogrammen,” ibid., 18 (1906); “Spektrokomparator,” in Zeitschrift für Instrumentenkunde, 26 (1906), 205-217; “Tabellen für das Rowlandsche und für das internationale Wellenlängenspektrum,” in Abhandlungen der Königlichen Gesellschaft der Wissenschaften zu Göttingen, Mathematisch-Physikalische Klasse, 10 , no. 2 (1916), 1-78; “Die astronomischen Instrumente des Kardinals Nicolaus Cusanus,” ibid., no. 6 (1919), 1-56, with 12 tables. Hartmann also edited and wrote some parts of Kultur der Gegenwart, vol. III of Band Astronomie (Leipzig, 1921).

II. Secondary Literature. See P. Labitzke, “Johannes Hartmann,” in Vierteljahrsschrift der Astronomischen Gesellschaft, 72 (1937), 3-23. There is also an obituary of Hartmann in Monthly Notices of the Royal Astronomical Society, 97 (1937), 284-285.

Hans Christian Freiesleben