Sunspots and Terrestrial Magnetism¹

Abstract

FOR a long time it has been known that sunspot frequencies have had their counterpart on the earth in the disturbances exhibited by the magnetic elements on its surface. As the sunspot period is at least eleven years, and as the variations in sunspot phenomena in successive eleven-year periods are considerable, it follows that to get a comparison of normal means free from accidental effects, a large number of periods must be taken. The Kew magneto-graphs have been in almost continuous operation since 1858, and the connexion between sunspots and the absolute daily range of declination (the element most easily measured), for the first 42 years of their progress up to 1900 has already been discussed. The first of the memoirs under notice treats of the same phenomena and adds another 10 years to the comparison (1). The decade which is under discussion proved generally to be one of small magnetic disturbance and low sunspottedness. Anomalies were disclosed in 1903 and 1909, but were attributed to accidental magnetic disturbance enhancing what would otherwise have been normal years. The application of Wolf's formula, connecting magnetic range with sunspot numbers, also gives a small amplitude of the declination range corresponding to hypothetical zero sunspot numbers throughout the ten years.