in geometry, the straight line in a plain figure, about which it revolves, to produce or generate a solid; thus, if a semi-circle be moved round its diameter at rest, it will generate a sphere, the axis of which is that diameter.

Axis, in astronomy, is an imaginary right line supposed to pass through the centre of the earth, and the heavenly bodies, about which they perform their diurnal revolutions.

Axis in conic-sections, a right line dividing the section into two equal parts, and cutting all its ordinates at right angles. See CONIC SECTIONS.

Axis, in mechanics. The axis of a balance is that line about which it moves, or rather turns about. Axis of oscillation is a right line parallel to the horizon, passing through the centre about which a pendulum vibrates. See MECHANICS.

Axis in peritrochion, one of the five mechanical powers, consisting of a peritrochium or wheel concentric with the base of a cylinder, and moveable together with it about its axis. See MECHANICS.

Axis, in optics, is that particular ray of light coming from any object which falls perpendicularly on the eye. See OPTICS.

Axis, in architecture, spiral axis, is the axis of a twisted column drawn spirally, in order to trace the circumvolutions without.

Axis of the Ionic capital, is a line passing perpendicularly through the middle of the eye of the volute. See ARCHITECTURE.

Axis of a vessel is an imaginary right line passing through the middle of it perpendicularly to its base, and equally distant from its sides.

AZI

Axis, in anatomy, the second vertebra of the neck, so called from the head's turning on it like an axis.

Axis, in zoology. See CERVUS.