Modern magnetospheric physics owes its initial development to two great pioneers: Sydney Chapman and Hannes Alfvén (Figure 1), who took very different and contrasting approaches to their research activities. This caused one of the most memorable controversies in space physics during the 20th century.
The controversy was initiated formally by Alfvén  when he criticized a paper by D.F. Martyn entitled, “The Theory of Magnetic Storms and Auroras,” published in Nature in 1951. Alfvén stated: “Dr. Martyns treatment is founded on Chapman-Ferraro's theory of magnetic storms. It is not my intention to review here the objections to this theory, objections which I believe to be fatal—nor is it worthwhile to discuss the curious super structure which Dr. Martyn tried to erect on this weak ground.” Alfven's objections will be described after briefly providing the background on which the Chapman-Ferraro theory was constructed. It may be mentioned at the outset that Chapman, together with T. G. Cowling, was well recognized by his publication of a classical treatise, “The Mathematical Theory of Non-Uniform Gases” in 1953; and also, with J. Bartels, of “Geomagnetism” in 1940, while Alfv´en established himself by the publication of an inspirational book,“Cosmical Electrodynamics” in 1950.