169 Vol. VIII. No. 4. APRIL, 1900. Whole No. 74. THE VARIATION OF LATITUDE AT NEW YORK, AND A DE- J. K. REES. FOR POPULAR ASTRONOMY. In 1892 the Columbia University Observatory completed its arrangements with Professor Em. Fergola, Director of the Royal Observatory at Capodimonte, Naples, for making a series of observations to study the variation of latitude. The Naples Observatory was selected because its latitude differed only 3 minutes of arc from that of the Observatory at Columbia. The regular Observatory of the University was then situated in the middle of the block bounded by 49th and 50th Streets and Madison and Fourth Avenues, New York City. This Observatory was on top of the library building of the University, and within 250 feet of the New York Central and New Haven Railroad tracks. In 1892, the trustees of the University purchased the new site on Morningside Heights, occupied at that time by the Bloomingdale Insane Asylum. The Director of the Observatory was able to interest the authorities of the Asylum, and although the property did not at once pass under the control of the trustees of Columbia, the Asylum trustees allowed the building of a little latitude Observatory on the grounds. The new site was further north than the old Observatory and also provided a place not disturbed by railroads. Here was erected in the fall of 1892 a small circular building of brick about twelve feet in diameter, having in its roof a proper slit for meridian observations. In the building was placed a zenith telescope built by Wanschaff, of Berlin, under the general direction of Dr. Albrecht, of Potsdam. Dr. Albrecht also consented to examine the instrument before it was shipped. The Wanschaff zenith telescope has an aperture of 80 millimeters, and a focal length of 1 meter. It is provided with two latitude levels. The illumination is electric. The instrument was in place and ready for observation about April 1st, 1893. Inasmuch as all of the officers connected with the Observatory were charged with daily work in the Uni versity, it made it impossible for one person to do all the work of observing. Moreover, during the summer the Astronomical Department conducts a summer class which occupies nearly the whole time of two of the three officers. It was decided, therefore, to divide the work of observing among three persons, and observations were made every clear night. During the first year and a half all observers lived about three miles away from the latitude Observatory, and it was necessary to make arrangements to sleep at the Asylum. Dr. Lyon, the superintendent of the Asylum, gave us every facility and comfort. Later on when the Asylum buildings were torn down to make way for the new University buildings, other arrangements had to be made. In December, 1895, the latitude Observatory had to be moved to make way for one of the University buildings. The new resting place was several hundred feet north and west of the first position, to which it was connected by a carefully executed survey. The two Observatories here and in Naples, being on very nearly the same parallel of latitude, were able to use the same stars. Four groups of stars were selected, seven pairs of stars in each group, and they were so arranged that the observations could be made for a determination of the constant of aberration by Küstner's method. The foregoing table gives the list of stars observed. From May 1st, 1893, to July 1st, '94, the observations were made every clear night. After the latter date it was decided to observe four clear nights each half month, whenever possible. All of the observations were made by J. K. Rees, H. Jacoby, and H. S. Davis. For the purpose of reduction our observations were divided into four series as follows: Series A. April 24, 1892 to July, 1894............................. 818 pairs by Rees. Jacoby. "Davis. "Rees. "Davis. This table shows the individual observers to have measured: |