RADIUS
, in Geometry, the semidiameter of a circle; or a right line drawn from the centre to the circumference.—It is implied in the definition of a circle, and it is apparent from its construction, that all the radii of the same circle are equal.—The Radius is sometimes called, in Trigonometry, the Sinus Totus, or whole sine.
Radius, in the Higher Geometry. Radius of the Evoluta, Radius Osculi, called also the Radius of concavity, and the Radius of curvature, is the right line CB, representing a thread, by whose evolution from off the curve AC, upon which it was wound, the curve AB is formed. Or it is the Radius of a circle having the same curvature, in a given point of the curve at B, with that of the curve in that point. See CURVATURE and Evolute, where the method of finding this Radius may be seen.
Radius Astronomicus, an instrument usually called Jacob's Staff, the Cross-staff, or Fore-staff.
Radius, in Mechanics, is applied to the spokes of a wheel; because issuing like rays from its centre.
Radius, in Optics. See Ray.
Radius Vector, is used for a right line drawn from the centre of force in any curve in which a body is supposed to move by a centripetal force, to that point of the curve where the body is supposed to be.
