Axis

Axis, aks′is, n. the axle, or the line, real or imaginary, on which a body revolves: the straight line about which the parts of a body or system are systematically arranged, or which passes through the centre of all the corresponding parallel sections of it, as of a cylinder, globe, or spheroid. The axis of a curved line is formed by a right line dividing the curve into two symmetrical parts, as in the parabola, ellipse, and hyperbola:—pl. Axes (aks′ēz).—adj. Ax′ial.—adv. Ax′ially.—n. Ax′oid, a curve generated by the revolution of a point round an advancing axis.—Axis of a lens, the right line passing through a lens in such a manner as to be perpendicular to both sides of it; Axis of a telescope, a right line which passes through the centres of all the glasses in the tube; Axis of incidence, the line passing through the point of incidence perpendicularly to the refracting surface; Axis of refraction, the continuation of the same line through the refracting medium; Axis of the equator, the polar diameter of the earth, which is also the axis of rotation; Axis of the eye, the right line passing through the centres of the pupil and the crystalline lens. [L. axis; cf. Gr. axōn, Sans. aksha, A.S. eax.]