Sun-spots and Terrestrial Magnetism

Abstract

PROF. PIAZZI SMYTH will no doubt welcome from any quarter a satisfactory answer to his question about the discrepancy between Dr. Wolf's sun-spot period, 11.1 years, and the supposed 10.5 years' period for the magnetic needle. If Mr. Smyth will refer to Prof. Loomis's chart of magnetic oscillations given in Prof. Balfour Stewart's paper on the subject in NATURE (vol. xvi. p. 10), he will see that there are exactly seven minimum-periods from 1787 to 1871, the mean of which is twelve years; the mean of the seven corresponding maximum-periods is 11.8 years. The true magnetic declination-period is then the mean of these, viz., 11.9 years. In exactly the same manner I have found that the mean period of sun-spots is 11.9 years. The auroral displays also have the same period.