The Recurrence of Magnetic Storms

Abstract

IN recent communications to the French Academy of Sciences Prof. H. Deslandres (see NATURE, vol. 118, p. 71), the distinguished director of the Meudon Observatory, has described a tendency in magnetic storms to follow one another at intervals iT/6, where i is integral, T being the rotation period shown by sunspots. It is now, I think, generally agreed that there is a tendency to a repetition in magnetic conditions, whether disturbed or quiet, in what is described for brevity as the 27-day interval. Investigations (Phil. Trans. A, vol. 212, p. 75, and A, vol. 213, p. 245) which I made in 1912 and 1913 showed a tendency to recurrence in intervals which were multiples of T, but in none shorter. Supposing in accordance with modern ideas, as seems to have been first suggested by Kr. Birkeland, that magnetic storms are due to the discharge of ions from the sun, if such discharge, whether from sunspots or other approximately fixed limited areas, went on for a long time, a repetition of disturbance according to the solar rotation period is exactly what we should expect. But repetition at intervals submultiples of T would suggest a different explanation, namely, that the sun as a whole acts somewhat like an intermittent geyser. The subject seemed so important both to magneticians and astronomers that I have further considered it.