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The Collaborative International Dictionary of English v.0.48 (gcide)

Octant \Oc"tant\, n. [L. octans, -antis. fr. octo eight. See
{Octave}.]
1. (Geom.) The eighth part of a circle; an arc of 45 degrees.
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2. (Astron. & Astrol.) The position or aspect of a heavenly
body, as the moon or a planet, when half way between
conjunction, or opposition, and quadrature, or distant
from another body 45 degrees.
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3. An instrument for measuring angles (generally called a
{quadrant}), having an arc which measures up to 9O[deg],
but being itself the eighth part of a circle. Cf.
{Sextant}.
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4. (Math. & Crystallog.) One of the eight parts into which a
space is divided by three coordinate planes.
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Quadrant \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.
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2. (Geom.) The quarter of a circle, or of the circumference
of a circle, an arc of 90[deg], or one subtending a right
angle at the center.
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3. (Anal. (Geom.) One of the four parts into which a plane is
divided by the coordinate 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.
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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[deg], 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.
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{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.
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