Activity of the Earth's magnetism in 1915

Abstract

At the meeting of the International Commission for Terrestrial Magnetism held at Innsbruck in 1905 a resolution was adopted recommending that magnetic observatories classify each day according to its magnetic character as quiet, moderately disturbed, or severely disturbed, using the notation 0, 1, and 2 for this purpose. This recommendation has been adopted by different observatories, one after another, so that now nearly all of the prominent observatories are sending quarterly reports of the magnetic character of days to the Netherlands Meteorological Institute and that institution is publishing them, thus making the data available for all. While this method of characterization is necessarily rough and influenced by the personal equation of the observer, yet the mean of a large number of estimations (between 35 and 40 at the present time) gives a very good idea of the relative magnetic condition of the whole earth from day to day. It does not, however, give an absolute measure of the daily fluctuations of the earth's magnetism nor does it permit a comparison of conditions in different parts of the earth.