2. Results of the Makerstoun Observations, No. 1. On the Relation of the Variations of the Earth's Magnetism to the Solar and Lunar Periods

Extract

The observations from which the following results are deduced, were obtained during the years 1844 and 1845, by means of the bifilar magnetometer, described in the Makerstoun Observations for 1841 and 1842; they are corrected for temperature by a method previously described.

From the Observations for the year 1844, the diurnal variation of the horizontal force is found to consist of two maxima and two minima; the minimum occurs at 10^h 20^m A.M. (Makerstoun mean solar time is used throughout), the maximum at 5^h 30^m P.M.; a minimum occurs at 2^h 20^m A.M., and a maximum at 5^h 30^m, or 40^m A.M.: two inflexions occur in the mean curve between 3^h and 4^h P.M., and between 8^h and 9^h P.M. The periods of maxima and minima vary throughout the year, and the morning maximum is greater than the afternoon maximum in winter.