Julius Bartels was born August 17, 1899 in Magdeburg, Germany. He studied mathematics, physics and geography in Berlin and Göttingen. After achieving his PhD in 1923, Bartels worked as a postdoc with A. Schmidt at the Potsdam magnetic observatory. His early works dealt with statistical methods especially in atmospheric, geomagnetic and ionospheric tides.

In 1928, Bartels became professor in Eberswalde; in 1936, he became director of the Potsdam Geophysical Institute and full professor at Berlin university. Between 1931 and 1940, he also worked as a research associate at the Department of Terrestrial Magnetism at the Carnegie Institution (Washington D.C., U.S.A.) for longer periods of time. In 1946, J. Bartels became professor in Göttingen, and, in addition, he was director of the Institute for Physics of the Stratosphere at the Max-Planck-Institut für Aeronomie in Lindau, Germany from 1955 to 1964 (Today: Max Planck Institute for Solar System Research).

In 1940, Bartels and his friend S. Chapman published Geomagnetism, a standard work of geophysics until today. In many of his publications, Bartels developed, used and perfected statistical methods. With these statistical methods, he was able to disprove many widely accepted geophysical models on the one hand and develop some very useful and easy to apply geophysical indices on the other. Among these widely accepted and well known indices is the planetary geomagnetic Kp index.

Eliminating regular variations of the Earth's magnetic field, he showed the impact of the Sun's wave and particle radiation. He recognized that seizing this concept in numbers would form a powerful tool for scientists in the research of solar-terrestrial relations. Bartels knew well that this the Kp tables would only be accepted if they were presented in a clearly arranged and lucid manner. The striking success of the three-hourly geomagnetic Kp indices is also due to their brilliant representation in the Bartels musical diagram (musical scales).

Using only geomagnetic data and statistical methods, Bartels claimed the existence of M-regions on the sun that are responsible for geomagnetic activity. Not before 1973 - with the Skylab mission - was observational data of coronal holes gained. The claimed M-regions were identified as coronal holes, which are the source of the fast solar wind that intensifies geomagnetic activity.

Julius Bartels was one of the initiators of the International Geophysical Year (IGY, 1957). When he died March 6, 1964, he had contributed much to the reputation of geophysics worldwide.

The Solar-Terrestrial Sciences section of the European Geophysical Society (EGS) has established the Julius Bartels Medal in recognition of the scientific achievement of Julius Bartels. It is reserved for outstanding research in solar-terrestrial sciences.

Biographical information extracted from W. Dieminger, Julius Bartels (Nachruf), in Mitteilungen aus der Max-Planck-Gesellschaft 1-2, München 1964, and W. Kertz, Einführung in die Geophysik II, Mannheim 1971.