Two volumes of proper motions have recently been received at the Observatory. Each has its particular scope. Nyren's "Proper Motions of 633 Stars," gives the computed values for a selected list of stars, nearly all of them being new, and mainly on this account nearly all of them of small size. Bossert's "Proper Motions of 5071 Stars/' includes all stars for which rehable values of proper motion of sensible amount have been computed, up to date. The Nyren catalog was prepared in order to furnish

more »

... the places and proper motions of the stars for a fundamental list, to be used in reducing the photographic measures of star places all over the sky. The aim was to provide at least one star, between fifth and seventh magnitude, on each photographic plate of 25 square degrees, between the north pole and 30 o south declination. From -30 o to the south pole the places and proper motions of the required stars are to be derived by Prof. Hough. A considerable proportion of the 1553 stars required for Nyren's list had already been discussed for proper motion, but there remained between 600 and 700 for which new values were to be computed. Some, for which the new computations were made, were later found among the other authorities, and for some of the stars there were not sufficient old observations to give rehable results for proper motion. The system adopted was that of the "New Fundamental Catalogue" of Dr. Peters, and ah the observations were reduced to this system, as far as possible* AU the stars were observed in recent years at the Poulkova Observatory, but owing to the break in the activities of that institution the results have been published in Volume 60 of the Swedish Academy of Sciences, for 1920. Ah available old catalogs have been employed in deriving the proper motions, going back more than a century, to those of Federenko, Piazzi and the Histoire Celeste. Often there were more than two dozen catalogs, from which observations could be obtained, for individual stars. Hah that number give a good determination. But for a few of the stars, observations were found in only three or four catalogs, and the resulting computed values are quite, uncertain, and sometimes of entirely doubtful character. The results of any combination of old observations depend, to a large extent, upon the respective weights assigned by the computor.