SEQUEL TO THE EPOCH OF HIPPARCHUS. 205 



mental question, Hipparchus undertook to construct 

 a Map of the heavens ; for though the result of his 

 survey was expressed in words, we may give this 

 name to his Catalogue of the positions of the most 

 conspicuous stars. These positions are described by 

 means of alineations ; that is, three or more such 

 stars are selected as can be touched by an apparent 

 straight line drawn in the heavens. Thus Hippar- 

 chus observed that the southern claw of Cancer, 

 the bright star in the same constellation which pre- 

 cedes the head of the Hydra, and the bright star 

 Procyon, were nearly in the same line. Ptolemy 

 quotes this and many other of the configurations 

 which Hipparchus had noted, in order to show that 

 the positions of the stars had not changed in the 

 intermediate time ; a truth which the catalogue of 

 Hipparchus thus gave astronomers the means of 

 ascertaining. It contained 1080 stars. 



The construction of this catalogue of the stars 

 by Hipparchus is an event of great celebrity in the 

 history of astronomy. Pliny 1 , who speaks of it with 

 admiration as a wonderful and superhuman task 

 (" ausus rem etiam Deo improbam, annumerare pos- 

 teris stellas") asserts the undertaking to have been 

 suggested by a remarkable astronomical event, the 

 appearance of a new star ; " novam stellam et aliam 

 in sevo suo genitam deprehendit ; ej usque motu, 

 qua die fulsit, ad dubitationem est adductus anne 

 hoc ssepius fieret, moverenturque et eae quas puta- 

 1 Hist. Nat. Lib. ii. (xxvi.) 



