in astronomy, a small apparent motion of the fixed stars, first discovered by Dr Bradley and Mr Mollineux, and found to be owing to the progressive motion of light, and the earth's annual motion in its orbit. If a lucid object be fixed, and the eye of the observer moving along in any other direction than that of a straight line from the eye to the object, it is plain, that the object must have an apparent motion, greater or less, according to the velocity with which the eye is moved, and the distance of the object from the eye. See Astronomy.

in optics, a deviation of the rays of light which prevents their uniting in the same focal point, and is occasioned by their being refracted by a spherical lens, or reflected by a spherical speculum. See Optics.