ASTEONOMY FOR 1889, 1890. 131 



The number of stars of which observations are recorded is 20,125; 

 so that when the stars enumerated in volume 2S of the Annals are reck- 

 oned, the total number of stars observed reaches 20,982. Measures 

 Lave also been made of 166 variable stars and of several planets and 

 satellites. In the " Harvard Photometry" the brightest stars were com- 

 pared solely with Polaris. lu the present observations A Ursie Minoris 

 was selected as the standard star, but the results are made to depend 

 upon a series of 100 circumpolar stars, the magnitudes of which were 

 frequently determined with the smaller instrument. 



FhotograpMc photometry. — The readiest and most effective means of 

 determining the magnitudes of stars from an examination of the disks 

 impressed on a sensitized film is a problem that has received much 

 attention recently, and contributions to the literature of the subject 

 have been made from the three observatories of Harvard, Stockholm, 

 and Potsdam. 



Professor Pickering gives in volume 18 of the Harvard Annals three 

 catalogues of magnitudes, embracing, on the whole, some 2,500 stars, 

 the first catalogue giving the photographic magnitudes of all the stars 

 brighter than the fifteenth magnitude within 1° of the pole; the second, 

 the magnitudes of many of the stars in the Pleiades ; and the third the 

 magnitudes of 1,131 stars generally brighter than the eighth magnitude 

 near the equator. 



The contribution from the Potsdam observatory is confined to the 

 discussion of the magnitudes of stars in tlie Pleiades as impressed on 

 plates taken with a chemically corrected object-glass by Dr. Scheiner, 

 and with the reflecting telescope of the Hereny observatory, supple- 

 mented by some photographs of the artificial stars in a Zollner photom- 

 eter. The principal results of the inquiry are twofold : first, that the 

 increase of the diameter of the star disk varies as the square root of 

 the time of exposure ; and secondly, that a simple linear relation exists 

 between the observed diameter and the magnitude. 



The third contribution to this subject is from Dr. Charlier, of Stock- 

 holm, who deduces a formula which expresses the connection between 

 the photographic brilliancy of a star and its photographed image in such 

 a manner as to insure a coincidence as far as possible between the pho- 

 tographic and photometric magnitudes. 



VARIABLE AND COLORED STARS. 



Ghandler^s catalogue of variable stars. — Chandler's admirable cata- 

 logue of variable stars has been adopted by Schoenfeld in the ephemer- 

 ides published in the Vierteljahrsschrift, and it also furnishes the data 

 for the ephemerides of the Anuuairedu Bureau des Longitudes and the 

 Observatory, and is thus formally recognized as the standard authority 

 ou variables. Mr. Chandler publishes in the Astronomical Journal 

 (No, 210) three tables supplementary to the catalogue, containing (1) a 

 list of new variables arranged as iij the original catalogue ; (2) a list of 



