Page:Scientific Memoirs, Vol. 2 (1841).djvu/75

Rh Mean Fluctuation of the Magnetic Declination during the three years from 1834 to 1837.

In reference to the single observations, Ave may here mention the greatest fluctuations which have occurred in the course of three years, in the forenoon and afternoon declinations. The greatest forenoon fluctuation was on the 8th of October, 1835, when the declination was about 20′ 1″ greater than on the 7th of October; and the greatest afternoon fluctuation occurred on the 24th of April, 1836, when the declination was 13′ 0″ greater than on the preceding day. On the other hand, perfect equality either of the forenoon or of the afternoon declinations, for two successive days, is a circumstance which has frequently occurred. In the monthly mean fluctuations these extremes naturally come much closer together; nevertheless, the great dissimilarity of the single months in this respect is still very remarkable, since, according to the above general view, the mean fluctuation in the forenoon declination in March, 1837, amounted to 6′ 6″; in December, 1836, only to 1′ 11″.

Whether, in general, greater fluctuations prevail at one time of the day than at others, cannot be determined with certainty, from the results of our observations of 8 and 1  Both are nearly equal in mean fluctuation for the first year; in the two following years the forenoon fluctuations exceed in amount, but the difference in the final results from the three years, 3′ 31″ and 3′ 3″, is too small to allow of any conclusion being yet {{hws|esta|established}