Nature 113, 105-112 (19 January 1924) | doi:10.1038/113105a0

Sun-spots as Magnets and the Periodic Reversal of their Polarity

GEORGE E. HALE

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THE revival of solar activity, now fairly begun after an interval of calm, prepares the way for a new attack on many classes of solar phenomena. Most important of these are the spots, of which the mode of origin and periodic variation in number and latitude are still unexplained. Recent observations at Mount Wilson, which have again shown the remarkable reversal of the magnetic polarity of sun-spots first detected at the opening of the last cycle of activity in 1912, now permit the formulation of the polarity law and help to define the conditions that must be recognised in any attempt to explain the constitution of the sun and other similar stars.