Close — Hipparchus and the Precession of the Equinoxes. 453 



us, we may perhaps be pardoned if we try to discover, for oiu'selves, 

 what reasons there may be which might lead to a settlement thereof. 



"We shall find that there are three arguments, of very different 

 kinds, which, it is submitted, lead undeniably to the conclusion that 

 Hipparchus considered that he had discovered the progression of the 

 stars, and not the retrogression of the equinoctial points. 



The first a/rgument is drawn from what we must believe to have 

 been the state of Hipparchus' mind respecting the question of the 

 immobility of the Earth. There can be no doubt that Hipparchus 

 shared the prevalent belief of his time in the immobility of the Earth, 

 and consequently in the diurnal rotation of the stellar firmament. It 

 is quite unnecessary to quote, as we could do, Lalande and others in 

 support of this. The only work of Hipparchus which has come down 

 to us — his commentaiy on the poem of Aratus on the Constellations — 

 gives no indication that his view difiered from the ordinary view 

 respecting the diurnal rotation of the firmament ; and his discussion of 

 the annual revolution of the Sun and of the monthly revolution of the 

 Moon round the Earth, as handed down to us by Ptolemy, shows that 

 he saw no difference as to the actual nature of both ; though he care- 

 fully discusses the difference of their details. Ptolemy was evidently 

 quite unconscious of any disagreement between Hipparchus and himself 

 on these points. 



If, then, Hipparchus could concede to the vault of heaven the 

 violently rapid diiu-nal rotation on the poles of the celestial equator, 

 which was contemplated by his contemporaries, he could have no 

 hesitation in. giving it a nearly opposite serenely slow rotation on the 

 poles of the ecliptic, once in nearly 26,000 years ; in order to explain 

 the precession of the equinoxes. From his point of view it would be 

 far more natural and reasonable to assign the newly-discovered gentle 

 motion to the already moving stellar finnament, than to give it to the 

 supposed stationary, perhaps immovable Earth, as woidd be reqtiired 

 by the retrogradation of the equinoctial points. This, of course, does 

 not prove that Hipparchus posited the progression of the stars ; but it 

 makes it exceedingly difficult to believe that he did not do so. It at 

 least shows that he would have a strong predisposition against 

 believing in the retrogradation of the equinoctial points. 



The second argument is drawn from the treatment of the statements 

 and expressions of Hipparchus, himself, by Ptolemy in his Almagest ; 

 where alone we can obtaia any authentic information on the subject. 



The places in that work which now concern us are Book iir., 

 chap. 2, and Book vii., chaps. 1, 2 and 3; but the best order of 



