COLURES

, are two great circles imagined to intersect at right angles in the poles of the world, and to pass, the one through the equinoctial points Aries and Libra, and the other through the solstitial points Cancer and Capricorn; from whence they are called the Equinoctial and Solstitial Colures. By thus dividing the ecliptic into four equal parts, they mark the four seasons, or quarters of the year.

It is disputed over what part of the back of Aries the equinoctial colure passed in the time of Hipparchus. Newton, in his Chronology, takes it to have been over the middle of the constellation. Father Souciet insists that it passed over the dodecatemorion of Aries, or midway between the rump and first of the tail. There are some observations in the Philos. Trans. number 466, concerning the position of this colure in the ancient sphere, from a draught of the constellation Aries, in the Aratæa published at Leyden and Amsterdam in 1652, which seem to confirm Newton's opinion; but the antiquity and authority of the original draught may still remain in question.