ASTEONOMY FOR 1889, 1800. 131 



The number of stai's of which observations are recorded is 20,125; 

 no that when the stars enntnerated in vohune 2t«5 of the Aunals are reck- 

 oned, the total nimiber of stars observed reaches 20,1)82. Measures 

 have also been made of IGO variable stars and of several planets aud 

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

 [)ared solely with Polaris. In the present observations A Ursa' Minoris 

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

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

 frequently determined with the smaller instruuumt. 



Photographic phototnefry. — The readiest aud most effective means of 

 determining the maguitudes of stars from an examination of the disks 

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

 attention recently, aud contributions to the literature of the subject 

 have been anide from the three observatories of Harvard^ Stockholm, 

 aud 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 tbe stars in the Pleiades ; and the third the 

 maguitudes 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 the Pleiades as impressed on 

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

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

 mented by some photographs of the artificial stars iu 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 observ^ed diameter aud the magnitude. 



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

 holm, who deduces a f )rmula which expresses the connection between 

 the i)hotographic 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. 



Chandler^s cataloijue 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 Annuairedu Bureau des Longitudes and the 

 Observatory, and is thus formally recognized as the standard authority 

 on variables. Mr. Chandler publishes in the Astronomical Journal 

 (No. 21(1) three tables su[)i)lementary to the catalogue, containing (1) a 

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



