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3. (Astron.) (a) The change in the direction of a ray of light, and, consequently, in the apparent position
of a heavenly body from which it emanates, arising from its passage through the earth's atmosphere; —
hence distinguished as atmospheric refraction, or astronomical refraction. (b) The correction which is
to be deducted from the apparent altitude of a heavenly body on account of atmospheric refraction, in
order to obtain the true altitude.
Angle of refraction (Opt.), the angle which a refracted ray makes with the perpendicular to the surface
separating the two media traversed by the ray. — Conical refraction (Opt.), the refraction of a ray of
light into an infinite number of rays, forming a hollow cone. This occurs when a ray of light is passed
through crystals of some substances, under certain circumstances. Conical refraction is of two kinds;
external conical refraction, in which the ray issues from the crystal in the form of a cone, the vertex
of which is at the point of emergence; and internal conical refraction, in which the ray is changed into
the form of a cone on entering the crystal, from which it issues in the form of a hollow cylinder. This
singular phenomenon was first discovered by Sir W. R. Hamilton by mathematical reasoning alone, unaided
by experiment. — Differential refraction (Astron.), the change of the apparent place of one object
relative to a second object near it, due to refraction; also, the correction required to be made to the observed
relative places of the two bodies. — Double refraction (Opt.), the refraction of light in two directions,
which produces two distinct images. The power of double refraction is possessed by all crystals except
those of the isometric system. A uniaxial crystal is said to be optically positive or optically negative
or to have positive, or negative, double refraction, according as the optic axis is the axis of least or
greatest elasticity for light; a biaxial crystal is similarly designated when the same relation holds for the
acute bisectrix. — Index of refraction. See under Index. — Refraction circle (Opt.), an instrument
provided with a graduated circle for the measurement of refraction. — Refraction of latitude, longitude,
declination, right ascension, etc., the change in the apparent latitude, longitude, etc., of a heavenly
body, due to the effect of atmospheric refraction. — Terrestrial refraction, the change in the apparent
altitude of a distant point on or near the earth's surface, as the top of a mountain, arising from the passage
of light from it to the eye through atmospheric strata of varying density.
Refractive
(Re*fract"ive) a. [Cf. F. réfractif. See Refract.] Serving or having power to refract, or turn
from a direct course; pertaining to refraction; as, refractive surfaces; refractive powers.
Refractive index. (Opt.) See Index of refraction, under Index. — Absolute refractive index (Opt.),
the index of refraction of a substances when the ray passes into it from a vacuum. — Relative refractive
index (of two media) (Opt.), the ratio of the sine of the angle of incidence to the sine of the angle of
refraction for a ray passing out of one of the media into the other.
Refractiveness
(Re*fract"ive*ness), n. The quality or condition of being refractive.
Refractometer
(Re`frac*tom"e*ter) n. [Refraction + -meter.] (Opt.) A contrivance for exhibiting and
measuring the refraction of light.
Refractor
(Re*fract"or) n. Anything that refracts; specifically: (Opt.) A refracting telescope, in which the
image to be viewed is formed by the refraction of light in passing through a convex lens.
Refractorily
(Re*frac"to*ri*ly) adv. In a refractory manner; perversely; obstinately.
Refractoriness
(Re*frac"to*ri*ness), n. The quality or condition of being refractory.
Refractory
(Re*frac"to*ry) a. [L. refractorius, fr. refringere: cf. F. refractaire. See Refract.]
1. Obstinate in disobedience; contumacious; stubborn; unmanageable; as, a refractory child; a refractory
beast.
Raging appetites that are
Most disobedient and refractory. Shak.
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