PORTION OF THE COSMOS. PHOTOMETRY. 79 



high antiquity so long ascribed to it, (between Autolycus of 

 Pitane and Timocharis, almost a century and a half, therefore, 

 before Hipparchus), we should possess in the astronomy 

 of the Greeks an indication of the time when the fixed stars 

 were not yet classed according to their relative brightness. 

 In the Catasterisms, in speaking of the stars which make 

 up a constellation, there is often a notice of the number of 

 those which are " brightest" or " largest" among them, while 

 others are said to be dark or little noticeable, ( 15 ) but 

 nothing is said of the stars in one constellation relatively to 

 those in another. According to Bernhardy, Baehr, and 

 Letronne, the Catasterisms are two centuries more modern 

 than the Catalogue of Hipparchus, and are a mere compila- 

 tion made without much care, an extract from the Poeticum 

 astronomicum ascribed to Julius Hyginus, if not from the 

 'E^ftj/e of the ancient Eratosthenes. The Catalogue of 

 Hipparchus, which we possess in the form given to it in the 

 Almagest, contains the first and important determination of 

 the classes of magnitude (degrees of brightness) of 1022 

 stars, or about l-5th of all the stars visible to the naked 

 eye in the whole heavens between the 1st and 6th magni- 

 tudes inclusive. Whether the estimations are exclusively 

 Hipparchus' s own, or whether they do not rather belong in 

 part to the observations of Timocharis or Aristyllus which 

 Hipparchus so often used, remains uncertain. 



This work formed the foundation on which the Arabians 

 and the whole of the middle ages continued to build ; and 

 even the habit which has been carried on into the 19th 

 century, of limiting the number of stars of the 1st magnitude 

 to 15 (Madler counts 18, and Rumker, after a careful exami- 

 nation of the southern heavens, above 20), is derived from 



