EQUANT, in astronomy, a fanciful circle, introduced into science to remove some of the defects of the Ptolemaic system of the universe. In this artificial system of epicycles and eccentric circles, the idea of circular and equable motion was by no means abandoned; but while each of the heavenly bodies revolved in its own orb, the centre of that orb was supposed to be carried at the same time round the circumference of another circle. The more obvious inequalities were thus explained with a geometrical precision. With all its nice combination, however, of circles, the system was soon found to have defects; to remove which, the fine contrivance of the equant was introduced. Though the angular motion of a planet viewed from the earth was confessed to be unequal, a point could be conceived from which it would be seen to move with perfect uniformity. That point was made the centre of the equant, and lay at the same distance from the centre of the eccentricity on the one side, as the earth was removed on the other. "Nothing (says Dr Smith, from whom this account of the equant is taken) can more evidently shew, how much the repose and tranquil-
ity of the imagination is the ultimate end of philosophy, than the invention of this equalizing circle."