VOL. XXXIV.] PHILOSOPHICAL TRANSACTIONS. IJ3 



liana, makes it; and above 500 years earlier than the time assigned by Sir Isaac 

 Newton. 



Now both of them making use of the same premises, it may seem strange 

 that their conclusions should be so widely distant; and indeed on a prepossession 

 that the Argonautic expedition, and the siege of Troy, could not have been 

 less than lOOO years before Christ, I must own, I was at first somewhat preju- 

 diced in favour of P. Souciet, taking his calculations for granted, and not having 

 seen Sir Isaac's work. But observing that he quotes Sir Isaac, as saying, that 

 in consequence of what Hipparchus has recorded from Eudoxus, the equinoc- 

 tial colure in the old sphere was about 7° 36' from the first star of Aries, I was 

 resolved to examine the matter with due attention, especially since the good 

 Father seems to triumph over his adversary, and to treat a man of his figure in 

 the commonwealth of learning in a very ludicrous manner, notwithstanding the 

 several fine things he says of him to palliate it. 



I find the dispute to be chiefly over what part of the back of Aries the colure 

 passed; the words of Hipparchus, as from Eudoxus, are simply, that it passed 

 over the back, without saying over what star, or over what part of the back it 

 passed. And the same Hipparchus shows, that if it passed over the star in the 

 middle of the back, it greatly differed from its situation in his time; and con- 

 ceiving thence that the equinoctial points might have a regressive motion, he 

 was the first that attempted to define their motion; but having no observations 

 older than those of Tymocharis, made within less than 200 years of his own 

 time, and very coarse withal, he was not able to determine its quantity, but 

 guessed it to be about a degree in 100 years; which length of time, and the 

 more curious observation of the moderns, has now proved to be 1° 24', or 

 rather 50' per annum. 



In a word, Sir Isaac takes the colure to have passed over the middle of the 

 constellation of Aries, and very near the star in the middle of the back, i- Bayero. 

 And P. Souciet will have it, that it passed over the middle of the sign of Dode- 

 catemorion of Aries, reckoning the sign to begin with the first star of the 

 constellation; and consequently his colure must pass about midway between the 

 rump and first of the tail of Aries, t and S Bayero, which situation could never 

 be said to be over the back; but while Sir Isaac makes the colure but 7° 36' 

 from the first star of Aries, which P. Souciet makes 15 degrees from it, the 

 difference 7° 24', at 50" per annum, makes 533 years difference in the result. 



Let us now examine when the stars in question did actually pass under the 

 colure of the vernal equinox, assuming their places as they are in Mr. Flam- 

 steed's British Catalogue, fitted to the beginning of the year l6yO. He places 

 the first star of Aries in 28° 51' of Aries, with 7° 9' north latitude. And sup 



