456 Proceedings of the Royal Iriah Academy. 



supposed that the sphere, in -^hich the stars seem to be fixed, has a 

 forward motion according to the succession of the signs. We have the 

 same also in Book in., chap. 2, near the beginning. This shoAVs 

 that Ptolemy took literally Hipparchus' language in the text of his 

 tractate, when he speaks of the forward motion of Spica Virginis, and 

 some other stars which he discusses, and that therefore he did not 

 take literally the title of that tractate. Ptolemy, who ought to 

 know, and doubtless did know, evidently believed that Hipparchus^ 

 opinion on the point in question was the same as his own, which 

 was that the phenomenon of the precession was produced by the 

 absolute, and not merely relative, progression of the stars. 



The tJiird argument is founded on an interesting temporary error of 

 Hipparchus, which was very soon coiTected by himself.^ Oidy a few 

 lines below the place last referred to, in the Almagest, we are told by 

 Ptolemy that when Hipparchus had examined only certain zodiacal 

 stars, and had observed their apparent progression, he supposed that 

 the extra-zodiacal stars did not participate in that progression. But 

 he could not possibly have supposed this had he believed in the retro- 

 gradation of the equinoctial points ; for that would give an apparent 

 progression to all the stars. He found afterwards, however, that the 

 stars outside the zodiac presei'ved their positions relatively to those 

 within it ; which, fi'om the sti'ong predisposition which he must 

 have had against the retrogression of the equinoctial points, would 

 mean for him that all the stars progressed together. 



It is submitted that these ai'guments, taken together, seem to make 

 it morally certain that Hippai'chus did not believe in. the actual 

 retro gradation of the equinoctial points. 



^ Mailin, ubi supra, p. 438, mentions tMs temporary en-or of Hipparclms ; 

 but, it is submitted, mates quite a -w-rong use of it, turning it into an argument to 

 favour tie contention of the members of Group B. Bailly, ubi supra, p. 108, also 

 seems to miss the point of it. 



