NUMBER OF THE FIXED STARS. 109 



star in Cassiopeia (November, 1572) led Tycho Brahe to 

 compose his catalogue of the stars. According to an ingen- 

 ious conjecture of Sir John Herschel,* the star referred to by 

 Pliny may have been the new star which appeared in Scorpio 

 in the month of July of the year 134 before our era (as we 

 learn from the Chinese Annals of the reign of "Wou-ti, of the 

 Han dynasty). Its appearance occurred exactly six years 

 before the epoch at which, according to Ideler's investiga- 

 tions, Hipparchus compiled his catalogue of the stars. Ed- 

 ward Biot, whose early death proved so great a loss to science, 

 found a record of this celestial phenomenon in the celebra- 

 ted collection of Ma-tuan-lin, which contains an account of 

 all the comets and remarkable stars observed between the 

 years B.C. 613 and A.D. 1222. 



The tripartite didactic poem of Aratus,t to whom we are 

 indebted for the only remnant of the works of Hipparchus 

 that has come down to us, was composed about the period of 

 Eratosthenes, Timocharis, and Aristyllus. The astronomical 

 non-meteorological portion of the poem is based on the ura- 

 nography of Eudoxus of Cnidos. The catalogue compiled by 

 Hipparchus is unfortunately not extant ; but, according to 

 Ideler,f it probably constituted the principal part of his work, 

 cited by Suidas, " On the arrangement of the region of the 

 fixed stars and the celestial bodies," and contained 1080 de- 

 terminations of position for the year B.C. 128. In Hippar- 

 chus' s other Commentary on Aratus, the positions of the stars, 

 which are determined more by equatorial armillse than by 

 the astrolabe, are referred to the equator by right ascension 

 and declination ; while in Ptolemy's catalogue of stars, which 

 is supposed to have been entirely copied from that of Hip- 

 parchus, and which gives 1025 stars, together with five so- 

 called nebulae, they are referred by longitudes and latitudes 



* Outlines, $ 831 ; Edward Biot, Sur les Etoilet Extraordinaire* ob- 

 servles en Chine, in the Connaissance des temps pour 1846. 



t It is worthy of remark that Aratus was mentioned with approba- 

 tion almost simultaneously by Ovid (Amor., i., 15) and by the Apostle 

 Paul at Athens, in an earnest discourse directed against the Epicureans 

 and Stoics. Paul (Acts, ch. xvii., v. 28), although he does not mention 

 Aratus by name, undoubtedly refers to a verse composed by him (Phccn., 

 v. 5) on the close communion of mortals with the Deity. 



\ Ideler, Untersuchungen fiber den Unsprung der Stemnamen, s. xxx. 

 xxxv. Daily, in the Mem. of the Astron. Soc., vol. xiii., 1843, p. 12 and 

 15, also treats of the years according to our era, to which we must refer 

 the observations of Aristyllus, as well as the catalogues of the stars com- 

 piled by Hipparchus (128. and not 140, B.C.) and by Ptolemy (138 

 AD.). 



