INDUCTIVE EPOCH OF HIPPARCHUS. 201 



The distinctness with which Hipparchus con- 

 ceived this change of relation of the heavens, is 

 manifested by the question which, as we are told by 

 Ptolemy, he examined and decided ; that this mo- 

 tion of the heavens takes place about the poles of the 

 ecliptic, and not about those of the equator. The 

 care with which he collected this motion from the 

 stars themselves, may be judged of from this, that 

 having made his first observations for this purpose 

 on Spica and Regulus, zodiacal stars, his first suspi- 

 cion was that the stars of the zodiac alone changed 

 their longitude, which suspicion he disproved by the 

 examination of other stars. By his processes, the 

 idea of the nature of the motion, and the evidence 

 of its existence, the two conditions of a discovery, 

 were fully brought into view. The scale of the 

 facts which Hipparchus was thus able to reduce to 

 law, may be in some measure judged of, by recol- 

 lecting that the precession, from his time to ours, 

 has only carried the stars through one sign of the 

 zodiac ; and that, to complete one revolution of the 

 sky by the motion thus discovered, would require a 

 period of 25,000 years. Thus this discovery con- 

 nected the various aspects of the heavens at the 

 most remote periods of human history; and, ac- 

 cordingly, the novel and ingenious views which 

 Newton published in his chronology, are founded 

 on this single astronomical fact, of the Precession of 

 the Equinoxes. 



The two discoveries which have been described, 



