Quad"rant (?), n. [L. quadrans, -antis, a fourth part, a fourth of a
whole, fr. quattuor four: cf. F. quadrant, cadran. See Four, and cf.
Cadrans.] 1. The fourth part; the quarter. [Obs.] Sir T. Browne.
2. (Geom.) The quarter of a circle, or of the circumference of a
circle, an arc of 90∞, or one subtending a right angle at the center.
3. (Anal. (Geom.) One of the four parts into which a plane is divided
by the coˆrdinate axes. The upper right-hand part is the first
quadrant; the upper left-hand part the second; the lower left-hand part
the third; and the lower right-hand part the fourth quadrant.
4. An instrument for measuring altitudes, variously constructed and
mounted for different specific uses in astronomy, surveying, gunnery,
etc., consisting commonly of a graduated arc of 90∞, with an index or
vernier, and either plain or telescopic sights, and usually having a
plumb line or spirit level for fixing the vertical or horizontal
direction.
Gunner's quadrant, an instrument consisting of a graduated limb, with a
plumb line or spirit level, and an arm by which it is applied to a
cannon or mortar in adjusting it to the elevation required for
attaining the desired range. -- Gunter's quadrant. See Gunter's
quadrant, in the Vocabulary. -- Hadley's quadrant, a hand instrument
used chiefly at sea to measure the altitude of the sun or other
celestial body in ascertaining the vessel's position. It consists of a
frame in the form of an octant having a graduated scale upon its arc,
and an index arm, or alidade pivoted at its apex. Mirrors, called the
index glass and the horizon glass, are fixed one upon the index arm and
the other upon one side of the frame, respectively. When the instrument
is held upright, the index arm may be swung so that the index glass
will reflect an image of the sun upon the horizon glass, and when the
reflected image of the sun coincides, to the observer's eye, with the
horizon as seen directly through an opening at the side of the horizon
glass, the index shows the sun's altitude upon the scale; -- more
properly, but less commonly, called an octant. -- Quadrant of altitude,
an appendage of the artificial globe, consisting of a slip of brass of
the length of a quadrant of one of the great circles of the globe, and
graduated. It may be fitted to the meridian, and being movable round to
all points of the horizon, serves as a scale in measuring altitudes,
azimuths, etc.
Quad*ran"tal (?), a. [L. quadrantalis containing the fourth fourth part
of a measure.] (Geom.) Of or pertaining to a quadrant; also, included
in the fourth part of a circle; as, quadrantal space.
Quadrantal triangle, a spherical triangle having one side equal to a
quadrant or arc of 90∞. -- Quadrantal versor, a versor that expresses
rotation through one right angle.
Quad*ran"tal, n. [L.] 1. (Rom. Antiq.) A cubical vessel containing a
Roman cubic foot, each side being a Roman square foot; -- used as a
measure.