S. K. Runcorn’s Commentary

Abstract

I went to Manchester University as an assistant lecturer in September, 1946 to work on cosmic rays and in the first term helped G. D. Rochester and C. C. Butler to get working a cloud chamber triggered by Geiger counters with which later they made notable discoveries in elementary particle physics. However, in November P. M. S. Blackett gave a colloquium on his theory of the geomagnetic field and I recall how surprised I, and others were, that such a commonplace natural phenomenon as the Earth’s field had never been given an explanation which could stand up to the slightest critical evaluation. So many of us took Blackett’s proposal that the field was a new fundamental property of rotating matter seriously — Einstein’s efforts to unify gravitation and electromagnetism were much talked of — and we discussed possible experimental tests. Some did not: I think geophysicists were somewhat embarrassed that such an important problem had not been given the slightest attention. Stimulated by Bullard’s suggestion that Blackett’s theory might be tested because it would predict a different variation of the field with depth, I worked out a theoretical prediction (as did Chapman more exactly). We planned to test the theory by comparing the geomagnetic field at the surface and in deep mines. It was necessary to have quite a team and A. C. Benson and A. F. Moore and I carried through the experiment with the enthusiastic assistance of undergraduate students of whom F. J. Lowes and R. Hide gained their first interest in geophysics. Blackett’s theory stimulated much interest (see my contribution in Notes of the Royal Society). Meanwhile W. M. Elsasser had written the fundamental papers of the dynamo theory. Frank Lowes soon got interested in the complexities of the dynamo and soon showed the relevance of laboratory experiments, first to the secular variation and then to the main field. Model experiments are difficult to make relevant in geophysics and I heard Sydney Chapman say that W. Gilbert with his terella had made the only successful model experiment in geophysics. Lowes and Wilkinson have been more successful than most, e.g. throwing light on reversals. Had they believed more in their model they could have predicted the short term geomagnetic events before they were discovered in the geological record! I am hardly in a position to criticize as I wrote papers in the early 1960’s arguing for the existence of a lunar core but did not predict that the Apollo rocks would be magnetized: Velikovsky apparently has that achievement to his credit!