Our Astronomical Column

Abstract

THE VARIATION OF LATITUDE AT PULKOVA. —Astronomische Nachrichten, No. 3112, contains two communications on the variation of the latitude at Pulkova, the first by Mr. B. Wanach, who discusses some old observations, and the second by Mr. S. Kostinsky, who has continued the former's recent observations made before July, 1891. During the years 1890 and 1891, Mr. Wanach obtained some very definite results with regard to this question by using the large Pulkova transit instrument in the Prime Vertical, and the object of the present discussion is to find out if any like result can be discovered. The observations used are those of W. Struve made between the years 1840-55, O. Struve 1858-9, Oom 1861-63, and Nyren 1879-82. If we employ those made in the years 1840˙42 it is at once noticed that to satisfy the conditions a variation in the height of the pole of ±o″˙1 has to be assumed, while the maxima and minima occur at different months of the year, the latter on September, 1840, May, 1841, March, 1842, and the former on January, 1841, September, 1841, and October, 1842. The observations from 1843˙63 present no direct fluctuations in the value of the mean pole height, but show that it remains constant or is proportional to the time during the whole period. Taking the values of the mean pole height for the years 1879-82, as obtained from a similar curve, it is found that a single sinus curve is not sufficient for the comparison; secondly, that the mean pole height is not the same as it was in 1841 and 1891, but is about o″˙15 greater; thirdly, that the chief maximum on March, 1881 coincides with the chief minimum on September, 1880, that is, exactly coincides with the phases of the pole height. It also happens that the series, which take more than two years, give only one distinct maximum and minimum (instead of two, as would be expected). Coming now to Mr. S. Kostinsky's work, whose observations were made by W. Struve's method with the aid of a large transit instrument by Repsold, the variation of latitude is clearly shown. With the aid of the curve, which accompanies the paper, the maximum of the latitude occurs on October 4, 1891. Owing to the observations not being quite complete, the epoch of minimum is uncertain, but the curve shows that it will take place somewhere before the end of the month of May 1892. Comparing this curve with that obtained by Mr. Wanach in the year 1891, we have for the dates of the greatest and least values of the latitude—