Refraction \Re*frac"tion\ (r?*fr?k"sh?n), n. [F. r['e]fraction.]
1. The act of refracting, or the state of being refracted.
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2. The change in the direction of ray of light, heat, or the
like, when it enters obliquely a medium of a different
density from that through which it has previously moved.
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Refraction out of the rarer medium into the denser,
is made towards the perpendicular. --Sir I.
Newton.
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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.
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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 (like quartz), or optically
negative (like calcite), 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.
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Double \Dou"ble\ (d[u^]b"'l), a. [OE. doble, duble, double, OF.
doble, duble, double, F. double, fr. L. duplus, fr. the root
of duo two, and perh. that of plenus full; akin to Gr.
diplo`os double. See Two, and Full, and cf. Diploma,
Duple.]
1. Twofold; multiplied by two; increased by its equivalent;
made twice as large or as much, etc.
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Let a double portion of thy spirit be upon me. -- 2
Kings ii. 9.
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Darkness and tempest make a double night. --Dryden.
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2. Being in pairs; presenting two of a kind, or two in a set
together; coupled.
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[Let] The swan, on still St. Mary's lake,
Float double, swan and shadow. --Wordsworth.
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3. Divided into two; acting two parts, one openly and the
other secretly; equivocal; deceitful; insincere.
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With a double heart do they speak. -- Ps. xii. 2.
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4. (Bot.) Having the petals in a flower considerably
increased beyond the natural number, usually as the result
of cultivation and the expense of the stamens, or stamens
and pistils. The white water lily and some other plants
have their blossoms naturally double.
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Note: Double is often used as the first part of a compound
word, generally denoting two ways, or twice the number,
quantity, force, etc., twofold, or having two.
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Double base, or Double bass (Mus.), the largest and
lowest-toned instrument in the violin form; the
contrabasso or violone.
Double convex. See under Convex.
Double counterpoint (Mus.), that species of counterpoint or
composition, in which two of the parts may be inverted, by
setting one of them an octave higher or lower.
Double court (Lawn Tennis), a court laid out for four
players, two on each side.
Double dagger (Print.), a reference mark ([dag]) next to
the dagger ([dagger]) in order; a diesis.
Double drum (Mus.), a large drum that is beaten at both
ends.
Double eagle, a gold coin of the United States having the
value of 20 dollars.
Double entry. See under Bookkeeping.
Double floor (Arch.), a floor in which binding joists
support flooring joists above and ceiling joists below.
See Illust. of Double-framed floor.
Double flower. See Double, a., 4.
Double-framed floor (Arch.), a double floor having girders
into which the binding joists are framed.
Double fugue (Mus.), a fugue on two subjects.
Double letter.
(a) (Print.) Two letters on one shank; a ligature.
(b) A mail requiring double postage.
Double note (Mus.), a note of double the length of the
semibreve; a breve. See Breve.
Double octave (Mus.), an interval composed of two octaves,
or fifteen notes, in diatonic progression; a fifteenth.
Double pica. See under Pica.
Double play (Baseball), a play by which two players are put
out at the same time.
Double plea (Law), a plea alleging several matters in
answer to the declaration, where either of such matters
alone would be a sufficient bar to the action. --Stephen.
Double point (Geom.), a point of a curve at which two
branches cross each other. Conjugate or isolated points of
a curve are called double points, since they possess most
of the properties of double points (see Conjugate). They
are also called acnodes, and those points where the
branches of the curve really cross are called crunodes.
The extremity of a cusp is also a double point.
Double quarrel. (Eccl. Law) See Duplex querela, under
Duplex.
Double refraction. (Opt.) See Refraction.
Double salt. (Chem.)
(a) A mixed salt of any polybasic acid which has been
saturated by different bases or basic radicals, as the
double carbonate of sodium and potassium,
NaKCO3.6H2O.
(b) A molecular combination of two distinct salts, as
common alum, which consists of the sulphate of
aluminium, and the sulphate of potassium or ammonium.
Double shuffle, a low, noisy dance.
Double standard (Polit. Econ.), a double standard of
monetary values; i. e., a gold standard and a silver
standard, both of which are made legal tender.
Double star (Astron.), two stars so near to each other as
to be seen separate only by means of a telescope. Such
stars may be only optically near to each other, or may be
physically connected so that they revolve round their
common center of gravity, and in the latter case are
called also binary stars.
Double time (Mil.). Same as Double-quick.
Double window, a window having two sets of glazed sashes
with an air space between them.
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