Ra"di*us (rā"d&ibreve;*ŭs),
n.; pl. L. Radii (-
ī); E. Radiuses (-ŭs*&ebreve;z). [L., a
staff, rod, spoke of a wheel, radius, ray. See Ray a divergent
line.] 1. (Geom.) A right line drawn or
extending from the center of a circle to the periphery; the
semidiameter of a circle or sphere.
2. (Anat.) The preaxial bone of the
forearm, or brachium, corresponding to the tibia of the hind limb. See
Illust. of Artiodactyla.
&fist; The radius is on the same side of the limb as the thumb, or
pollex, and in man it is so articulated that its lower end is capable
of partial rotation about the ulna.
3. (Bot.) A ray, or outer floret, of
the capitulum of such plants as the sunflower and the daisy. See
Ray, 2.
4. pl. (Zoöl.)
(a) The barbs of a perfect feather.
(b) Radiating organs, or color-markings, of the
radiates.
5. The movable limb of a sextant or other
angular instrument. Knight.
Radius bar (Mach.), a bar pivoted at
one end, about which it swings, and having its other end attached to a
piece which it causes to move in a circular arc. --
Radius of curvature. See under
Curvature.
