174 PHILOSOPHICAL TKANSACTONS. [aNNO 1/27. 



posing the obliquity of the ecliptic 23° 29', it will be, as radius to the tangent 

 of 23° 29' :: so the tangent of 7° 9', to the sine of 3° 7-i-', the dilference of 

 longitude between the star and the point in the ecliptic which passed under the 

 colure at the same time with the star; so that this point was the beginning of 

 the year 169O, in "jT 25° 43' 30", and therefore, allowing 50'' per annum, the 

 star was under the colure J 852 years before the epocha of the British Catalogue, 

 that is, 162 years before our sera of the nativity of Jesus Christ; in which 

 very year Hipparchus began to observe the equinoxes recorded by Ptolemy, 

 lib. 3, cap. 2. 



If therefore, with Sir Isaac, we add 7° 36' to the long, of the first star 01 

 Aries, as it was in 169O, we shall have 30° 27', which the colure moves in 2624 

 years, and deducting 169O, we shall have 934 years before Christ for the Argo- 

 nautic expedition. And if to 7° 36 we add 3° 7-i-', we shall have lO'^ 43-i-', 

 that is, 772 years before the first star of Aries passed the colure. 



Next let us inquire when the star in the middle of the back of Aries, v 

 Bayero, passed the colure. Its longitude anno l6go ineunte, was 9° 48' 35" 

 of Taurus, with north lat. 0" 8'; but by the foregoing analogy, the point in 

 the ecliptic, over which the colure passed at the same time with it, was 2° 40-^' 

 before it, that is, in y 7° 8'. Now 37° 8' give 2674 years nearly, or g84 years 

 before Christ, when that star was under the equinoctial colure, being but half 

 a century earlier than Sir Isaac places the Argonautic expedition; and shows 

 that he took the middle of Aries over which the colure is supposed to have 

 passed, to be the middle of the constellation, and not of the Dodecatemorion, 

 and in so doing, no doubt, had reason to place this colure 7° 36' in consequence 

 of the first star of Aries, instead of 8° 17', as it was when the star in the 

 middle of the back of Aries was under the colure. 



But if, with P. Souciet, we make the colure to intersect the ecliptic 15 

 degrees from the first star of Aries, or 43° 5l' from the equinoctial point, as 

 it was anno l6gO, we shall have the time nearly 1470 years before Christ; but 

 then the colure will be very far from the middle of the back of Aries, and 

 leave only his tail to the eastward, as it leaves the head of the whale to the 

 westward, so as by no means to agree with the description we have of it from 

 Hipparchus; which it were to be wished had been more definitive, and as well 

 circumstanced as what Hipparchus has left us of the position of the colures in 

 his own time, which on examination I find to be very consistent, and the obser- 

 vations made with sufficient care. 



Thus I hope, I have shown P. Souciet, that there was no affectation of mys- 

 tery in Sir Isaac's placing the colure 7° 36' from the first star of Aries,- nor any 

 occasion to drole as he does p. 131, 132, on that account; as also that lie ought 



