Magnetism and Sun-Spots

Abstract

WHEN Sir Edward Sabine was preparing his paper¹ “On Periodical Laws discoverable in the mean effects of the larger Magnetic Disturbances—No. ii.,” in which he discussed the magnetic observations made at the temporarily established Colonial observatories at Toronto and Hobarton, he found that there existed at these places, in the years 1843 to i 848, a progressive increase in amount both of magnetic disturbance and in extent of diurnal range of the declination magnet, the values of diurnal range for the year 1843 having become in 1848 increased by some 40 per cent., the Toronto values for these years being 8’˙90 and 12’˙11 respectively, and the Hobarton values 7’˙66 and 10’˙63. This was an altogether unlooked-for result, one that engaged his special attention, such increase of value from year to year in two quarters of the globe so widely separated as Toronto and Hobarton presumably indicating not simply a local effect, but one rather of cosmical character. He pointed out that as the sun must be recognised as at least the primary cause of all magnetic variations that conform to a law of local hours, as does the solar diurnal range, it seems not unreasonable to suppose that in the case of other magnetic variations we should look, in the first instance, to any periodical variation by which the sun is affected, to ascertain whether any coincidence of period or epoch is traceable. And he draws attention to the circumstance that, according to Schwabe's then recently-published table of frequency of solar spots, a minimum in number of spots occurred in 1843 and a maximum in 1848, with progressive increase in the intermediate years similar to that of the diurnal magnetic range during the same interval as shown by the Toronto and Hobarton observations. This led Sabine to infer the probable existence of a periodical variation in magnetism similar to that—one of about ten years—which Schwabe had detected in sun-spots from observations extending over a period of twenty-five years.