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Nature volume 50, pages 277278 | Download Citation



VARIATIONS OF LATITUDE.—Since 1885, the fifteen polar stars of which the apparent places are given in the Connaissance des Temps, have been regularly observed at Lyons Observatory. The materials thus obtained are used by M. F. Gonnessiat, in the Bulletin Astronomique (vol. xi. June and July 1894), for an investigation of the variations of latitude. The calculations show that from one maximum to the next the mean interval is 1.185 years; while the mean interval between two successive minima comes out as 1.178 years. In round numbers, therefore, the variation has a period of 1.18 years, that is, 431 days, which agrees with that found by Mr. Chandler. The mean amplitude of the oscillation is 0″.44. As to the annual variation, M. Gonnessiat is inclined to think that it has no real existence. He points out that one batch of observations discussed by Mr. Chandler, was like those made at Lyons, and hence refraction and errors of delineation introduce apparent annual changes in the results. In the case of observations made in the prime vertical by Horrebow's method, it is argued that refraction would show itself in the results, not only by its effects on the zenith distance of the same star in the course of a year, but also on the same day, when the connection between the groups observed is established. It is further remarked that the intensity of gravity, which determines the phase of the annual term, is far from being constant at any single place, and that its variation with the longitude does not appear to have been established. For these reasons M. Gonnessiat holds that it is necessary to exercise “une certaine reserve à l'égard du second terme de la formule de M. Chandler.”

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