(b. Magdeburg, Germany, 17 August 1899; d. Göttingen, Germany, 6 March 1964)
Bartels was educated at the University of Göttingen, graduating Ph.D. in 1923 and then working in close association with the distinguished geomagnetician Adolph Schmidt for four years. He was head of the Meteorological Institute at the Fortliche Hochschule in Eberswalde from 1927 to 1941, professor of geophysics at the University of Berlin from 1941 to 1945, and professor of geophysics and director of the Geophysical Institute of the University of Göttigen from 1945 on. From 1956 he was also director of the Max Planck Institute of Aeronomy at Lindau and, from 1954 to 1957, president of the International Association of Geomagnetism and Aeronomy.
At the time Bartels began his research, the mathematical theory of statistics was emerging as a major scientific tool. Bartels saw how it could be used to improve the quality of inferences in important sections of geomagnetism. Accordingly, he developed rigorous statistical procedures that both served as a pattern in subsequent geomagnetic analyses and led to new results of much importance. He himself applied the procedures skillfully and fruitfully.
Bartels’ statistical analyses led him to make the first clear discrimination between the geomagnetic variations caused by wave and particle radiation from the sun, and from this to develop reliable measures, based on geomagnetic observations, of the two types of radiation. Some of the indexes he introduced in his treatment of geomagnetic variations came to be used internationally, e.g., a sensitive geomagnetic index of the influx of solar particles into the auroral region and his planetary indexes Kp. His procedures further enabled Bartels to elucidate features of tides in the earth’s atmosphere that are caused by the moon’s gravitational attraction. In investigating twenty-seven-day variations in geomagnetic activity, which are connected with the sun’s rotation, he was led to postulate the existence in the sun of certain magnetically active regions (M regions), which astronomers later connected with the development of sunspots. He also showed that the sun’s surface is never wholly active or wholly quiet.
Among Bartels’ works are “Statistical Methods for Research on Diurnal Variations,” in Terrestrial Magnetism and Atmospheric Electricity, 37 (1932), 291–302; “Twenty-Seven-Day Recurrence in Terrestrial Magnetic and Solar Activity, 1932–33,” ibid., 39 (1934), 201–202; “Random Fluctuations, Persistence and Quasi-persistence in Geophysical and Cosmical Periodicities,” ibid., 40 (1935), 1–60; “The Eccentric Dipole Approximating the Earth’s Magnetic Field,” ibid., 41 (1936), 225–250; “Geophysical Lunar Almanac,” ibid., 43 (1938), 155–158, written with G. Fanselau; “Harmonic Analysis of Diurnal Variations for Single Days,” ibid., 44 (1939), 137–156; “Some Problems of Terrestrial Magnetism and Electricity,” in J. A. Fleming, ed., Physics of the Earth VIII: Terrestrial Magnetism and Electricity (New York-London, 1939), pp. 385–430; “The Three-Hour-Range Index Measuring Geomagnetic Activity,” in Terrestrial Magnetism and Atmospheric Electricity, 44 (1939), 411–454; Geomagnetism, 2 vols. (Oxford, 1940, 1951, 1962), written with Sydney Chapman; “Geomagnetic Data on Variations of Solar Radiation, Part I—Wave-radiation,” in Terrestrial Magnetism and Atmospheric Electricity, 51 (1946), 181–242; “Geomagnetic and Solar Data” in Journal of Geophysical Research, 54 (1949), 295–299; “Geomagnetically Detectable Local Inhomogeneities in Electrical Conductivity Below the Surface,” in Nachtrichten. Akademie der Wissenschaften in Göttingen, 5 (1954), 95–100; “Solar Influences on Geomagnetism,” in Proceedings of the National Academy of Sciences, 43 (1957), 75–81; and “Discussion of Time-variations of Geomagnetic Activity Indices Kp and Ap, 1932–1961,” in Annales de géophysique, 19 (1963), 1–20.
Bartels was also editor of Vols. XLVII and XLVIII of Handbuch der Physik (Berlin, 1957).
K. E. Bullen