AXIS, in geometry, the straight line in a plane figure about which it revolves, to produce or generate a solid : thus, if a semicircle be moved round its diameter at rest, it will generate a sphere, the axis of which is that diameter.
Axis, in astronomy. 1. Axis of the world, an imaginary right line conceived to pass through the centre of the earth, from one pole to the other, about which the sphere of the world, in the Ptolemaic system, revolves in its diurnal rotation. 2. The axis of a planet is that line drawn through the centre about which the pla net revolves. The sun, together with all planets, except Mercury, Saturn, and Herschel, are known, by observation, to move about their respective axes. The axis of the earth, during its revolution round the sun, remains parallel to itself, and is inclined to the plane of the eclip tic, making with it an angle of 66i de grees." 3. The axes of the equator, hori zon, ecliptic, zodiac, &c. are right lines drawn through the centres of those cir cles perpendicular to their planes.
Axis, in conic sections, a right line, di viding the section into two equal parts, and cutting all its ordinates at right an gles. See CONIC SECTIONS.
Axis, in mechanics. The axis of a ba lance is that line about which it moves, or rather turns about. Axis of oscilla tion is a right line parallel to the horizon, passing through the centre about which a pendulum vibrates.
Arts in per/Epoch/0, one of the five me chanical powers, consisting of a peritro chium or wheel, concentric with the base of a cylinder, and moveable together with it about its axis. See Mscussleg.
Axis, in optics, is that ray, among all others that are sent to the eye, which falls perpendicularly upon it, and which consequently passes through the centre of the eye.
Axis of a glass or lens, is a right line joining the middle points of the two op posite surfaces of the glass.
Axis of incidence, in dioptrics, is a right line perpendicular, in the point of incidence, to the refracting superficies, drawn in the same medium that the ray of incidence comes from.
Axis of refraction, is a right line drawn through the refracting medium, from the point of refraction, perpendicular to the refracting superficies.