Progress report of the committee on relations between terrestrial magnetism, terrestrial electricity, and solar activity

Abstract

Measures of Solar, Magnetic, and Electric Activity.—The compilation and computation of measures of solar activity, magnetic activity, and electric activity, based on all available data, have been continued by the Department of Terrestrial Magnetism. Thanks to the cooperation of Professor Wolfer of Zurich, we are promptly supplied with his relative sun‐spot numbers, which are published as soon as possible in the Journal of Terrestrial Magnetism and Atmospheric Electricity in order to make the data available to others. We have at present the final sun‐spot numbers through 1918 and the provisional ones complete from 1919 to March 1923, inclusive. From these data, it appears that for the present cycle, the minimum sun‐spot activity occurred in 1913, and an extraordinarily large maximum (103.9 for the mean of the year) in 1917; it is not yet possible to say whether the minimum has again been reached. The mean number for 1922 was 14.7, and the mean monthly numbers for January to March 1923 are, respectively: 5.3, 1.6, and 4.0. There has been no such high maximum as that of 1917 since 1870, when the mean number for the year was 139.1. For the first time since 1871 has the monthly mean number exceeded 150, as it did in August 1917, viz, 154.5.