Ionospheric research in Germany prior to Karl Rawer

This brief historical review summarizes the work and achievements of German researchers on ionospheric problems before Karl Rawer started his scientific career in 1937.


Introduction -basic milestones towards ionospheric research
A necessary prerequisite of any ionospheric research was the unification of electricity and magnetism by James Clerk Maxwell (1873).Since electromagnetic waves played a fundamental role in this research their discovery by Heinrich Hertz in 1887 was another basic milestone (Dittmar-Ilgen, 2007).Similarly important was the work by Karl Ferdinand Braun who fundamentally improved earlier radio wave transmitters and introduced the cathode ray tube (Zenneck, 1955).
The first practical encounter of electromagnetic waves with the ionosphere constituted 1901 the trans-atlantic radio signal transmissions by Guglielmo Marconi (Beckmann, 1974) which earned him the Nobel Price 1909 (together with the just mentioned K. F. Braun).In order to explain Marconi's results Arthur Edvin Kennelly and Oliver Heaviside postulated 1902 a conducting layer in the upper atmosphere (Beckmann, 1974).For completeness it should be mentioned here that already C. F. Gauss speculated in 1838 about such a layer inspired by his geomagnetic field investigations.It took more than two decades before the existence of this layer was experimentally proven by Edward Victor Appleton (Appleton and Barnett, 1925).Only two years later, 1926, Robert Watson-Watt coined the term ionosphere (Beckmann, 1974).
In the following we will sketch the early ionospheric work in Germany by focussing on the scientists who performed it.

Jonathan Zenneck
The most important and influential ionospheric pioneer in Germany was certainly Jonathan Zenneck (1871Zenneck ( -1959)), Karl Rawer called him the "father of the German ionospheric physics".Zenneck first studied theology and natural sciences at the University of Tübingen from 1889 to 1894 and received a PhD in zoology.He almost decided to become a zoologist, but discussions with the above mentioned K. F. Braun aroused his interest in HF techniques and he became an assistant of Braun at the University of Straßburg from 1895-1905.During this time he performed his first experiments in wireless telegraphy in order to establish a maritime radio service at the shore of the North Sea in Cuxhaven.In 1905 he published a textbook on wireless telegraphy, the first of this kind in Germany.
In the same year he received a call as "außerordentlicher" Professor to the University of Danzig.His time there was short, already in 1906 he became Professor at the Technical University of Braunschweig. From 1907to 1911 (Goubau and Zenneck, 1932).
in München, at night after the end of the regular programme.Only one year later he and his collaborators (G.Goubau, and others, see below) established their own research station on top of the Herzogenstand, a mountain near München.They built a first type of ionosonde capable of pulse sounding as well as continuous transmitting, and used for the first time Braun's cathode ray tube for diagnosis (Fig. 1a and b).Among their research subjects were -measurements of echo height and its daily and seasonal variations, A detailed description of the life and work of Zenneck (Fig. 2), including a complete list of his publications is given in Schmucker (1999).

Zenneck's important PhD students and collaborators
One of Zenneck's oldest PhD student and collaborator was Johannes Plendl , Fig. 3a.After finishing his PhD in 1925 he developed devices for long-range short-wave communication with the German company Telefunken, and from 1927 on at the "Deutsche Versuchsanstalt für Luftfahrt".In 1934 he became Director of the section F ("Flugfunk") of the military (German air force) "Erprobungsstelle" (test facility) in Rechlin (about 200 km north of Berlin), developing radio beam guiding systems (System "Knickebein").He also established regular radio wave propagation forecasts in "Gruppe I" of this section, and installed W. Dieminger (see below) as head of this group.In 1947 he came to the US with the "Operation Paperclip", working at the Air Force Cambridge Research Laboratory.After his retirement in 1970 he returned to Germany (for more details, see Seiler, 2007).
Georg Goubau (1906Goubau ( -1980)), Fig. 3b, was Zennecks's main collaborator in establishing and operating the research station Herzogenstand.In 1939 he became full Professor at the University of Jena and was engaged in the development of microwave techniques.More about Goubau can be found in his obituary (Schwering, 1981).
A student of Zenneck, very influential for ionospheric research, was Walter Dieminger , Fig. 3c.After his PhD in 1935 he became the head of the radio wave propagation unit of the "Erprobungsstelle Rechlin" (Group I of Section F).His group was very successful in providing propagation forecasts for the Germany military, which during WW2, was spread over whole Europe.His successful work was acknowledged by the American, British, and French forces, and after the war all three tried to capture his group.The British were successful and under the command of (the science officer) Roy Pigott (and with support from Apple-  ton) Dieminger's group was brought to the British sector, to Lindau/Harz (Gerwin, 1981).As a consequence of their important scientific achievements Dieminger's group became a member of the Kaiser-Wilhelm-Gesellschaft (KWG) in 1946.After the KWG was dissolved 1951 and re-established as Max-Planck-Gesellschaft, Dieminger became the Director of the Max-Planck-Institut für Aeronomie in Lindau and    of URSI.For more details about Dieminger, see Hartmann (2001).
Rudolf Eyfrig (1911Eyfrig ( -2011) ) was, after his PhD in 1937, an important collaborator of Zenneck at the research station Herzogenstand.After the war he was Director of the Ionospheric Research Office of the Deutsche Bundespost.Most of Eyfrig's publications are listed in Beckmann (1974).
Hans Rukop (1883Rukop ( -1958)), Fig. 3d, was not a PhD student of Zenneck, but of Richard Mie at the University of Greifswald.However he joined Zenneck during his time in Danzig and followed him to München in 1913 were both continued their successful scientific collaboration.His speciality was the development of vacuum tubes.Later Rukop became the Director of vacuum tube production at the Telefunken company (Blumentritt, 1955).

Other important German ionospheric scientists
Karl Försterling (1885Försterling ( -1960)), Fig. 4a, received his PhD at the University of Göttingen in 1909, since 1938 he was professor for theoretical physics at the University of Köln (Scheffczyk, 2011).He performed fundamental theoretical work on radio wave propagation mainly with Hans Lassen .Lassen published in 1926 his famous radio wave dispersion formula, known as Appleton-Lassen-Equation.
Hans Ernst Mögel (1900Mögel ( -1944) ) worked with Hans Barkhausen at the Technical University of Dresden and received his PhD there in 1927.After that he became the leader of the trans-continental wireless station Beelitz (south of Berlin) operated by Transradio a branch of Telefunken (Fritz Traxler, personal communication, 2011).In 1930 he published his famous paper about the absorption of radio waves in the D region during solar flares (sudden ionospheric disturbance, SID, Mögel, 1930).Although the American scientist John Howard Dellinger published similar results five years later in 1935 the corresponding phenomenon is called Mögel-Dellinger Effect. Karl Willy Wagner (1883-1953), Fig. 4b, received his PhD at the University of Göttingen in 1910 and was appointed Professor at the Technical University of Berlin in 1927.In the year 1930 he founded the Heinrich-Hertz-Institut in Berlin where important work on radio wave propagation and ionospheric investigations were performed in the following decades.Wagner was a participant in the International Polar Year 1932/33, and conducted important ionospheric investigations in Tromsö together with Harang and Appleton.More details about his work and life together with a complete list of his publications can be found in Frühauf (1956).His colleague Willy Stoffregen (1909Stoffregen ( -1987) ) a talented engineer and scientist developed the equipment for the measurements during the International Polar Year (Stoffregen, 1984).
Very little known in the scientific community is Bernhard Düll .He received his PhD at the University of Rostock 1932.He was a pioneer in establishing solarterrestrial relations, and published papers of solar influence not only on the ionosphere but also on weather and human mortality (see Halberg et al., 2013).
Very important for ionospheric research was Julius Bartels , Fig. 4c, although he mostly worked on geomagnetism.He received his PhD in 1923 at the University of Göttingen and then worked together with the famous geomagnetician Adolf Schmidt at the observatory of Potsdam.1928 he became Professor at Eberswalde and in 1936 Director of the Potsdam Magnetic Observatory.From 1946 until his retirement he was Professor for Geophysics at the University of Göttingen, and1955-1964 simultaneously Director of the Max-Planck-Institut für Stratosphärenphysik (section of the Max-Planck-Institut für Aeronomie, see previous section).His two-volume book "Geomagnetism" (together with Sidney Chapman) was and still is a widely referenced standard textbook (Chapman and Bartels, 1940).More details can be found in his biography written by Kertz (1965).
Last not least Arnold Sommerfeld , Fig. 4d, should be mentioned here, in particular since Karl Rawer was very impressed by his knowledge, his teaching and his seminars.Sommerfeld studied in Königsberg where he received his PhD in 1891.After professorships at the University of Göttingen and the Technical University of Aachen, he became 1906 professor for theoretical physics at the University of München where he stayed until his retirement.He did not publish specific papers on ionospheric physics, but on radio wave propagation.He also was a friend and respected colleague of Zenneck and took part in many discussions on ionospheric problems.