Abstract
LONDON
Royal Society, March 3.—The following papers were read: “Results of the monthly observations of dip and horizontal force made at the Kew Observatory from April 1863 to March 1866, inclusive,” by Dr. B. Stewart. The author exhibited tabular statements of dip observations during six years, from which was deduced the existence of a semi-annual inequality, in virtue of which the dip is on an average 0′.27 lower in the six months from April to September, and 0′.27 higher in the six months from October to March than is due to its mean value. This result is in the same direction as that found by Sir E. Sabine for the six years ending March 1863, but is less in amount than the latter, that determined from the first six years exhibiting a range of 1′31, while that determined from last six years only exhibits a range of 0′.54. From the first six years Ave deduce a mean dip equal to 68° 20′.07, corresponding to middle epoch April 1, 1860, and from the latter six, a mean dip equal to 68° 6′.62, corresponding to middle epoch April 1, 1866, while the secular change deduced from the first series is 2′.00, and that deduced from the last series is 1′.92, the mean of these two values being 1′.96. If we apply this mean value of the secular change to the mean result corresponding to the epoch April 1, 1860, in order to bring it to the epoch April 1, 1866, we obtain—
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Societies and Academies . Nature 1, 517–522 (1870). https://doi.org/10.1038/001517a0
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DOI: https://doi.org/10.1038/001517a0