n. 折光, 折射

[医] 折射, 屈光

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.

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.

Refraction out of the rarer medium into the denser,
is made towards the perpendicular. --Sir I.
Newton.

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 (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.

Angle \An"gle\ ([a^][ng]"g'l), n. [F. angle, L. angulus angle,
corner; akin to uncus hook, Gr. 'agky`los bent, crooked,
angular, 'a`gkos a bend or hollow, AS. angel hook, fish-hook,
G. angel, and F. anchor.]
1. The inclosed space near the point where two lines meet; a
corner; a nook.

Into the utmost angle of the world. --Spenser.

To search the tenderest angles of the heart.
--Milton.

2. (Geom.)
(a) The figure made by. two lines which meet.
(b) The difference of direction of two lines. In the lines
meet, the point of meeting is the vertex of the angle.

3. A projecting or sharp corner; an angular fragment.

Though but an angle reached him of the stone.
--Dryden.

4. (Astrol.) A name given to four of the twelve astrological
``houses.'' [Obs.] --Chaucer.

5. [AS. angel.] A fishhook; tackle for catching fish,
consisting of a line, hook, and bait, with or without a
rod.

Give me mine angle: we 'll to the river there.
--Shak.

A fisher next his trembling angle bears. --Pope.

{Acute angle}, one less than a right angle, or less than
90[deg].

{Adjacent} or {Contiguous angles}, such as have one leg
common to both angles.

{Alternate angles}. See {Alternate}.

{Angle bar}.
(a) (Carp.) An upright bar at the angle where two faces of
a polygonal or bay window meet. --Knight.
(b) (Mach.) Same as {Angle iron}.

{Angle bead} (Arch.), a bead worked on or fixed to the angle
of any architectural work, esp. for protecting an angle of
a wall.

{Angle brace}, {Angle tie} (Carp.), a brace across an
interior angle of a wooden frame, forming the hypothenuse
and securing the two side pieces together. --Knight.

{Angle iron} (Mach.), a rolled bar or plate of iron having
one or more angles, used for forming the corners, or
connecting or sustaining the sides of an iron structure to
which it is riveted.

{Angle leaf} (Arch.), a detail in the form of a leaf, more or
less conventionalized, used to decorate and sometimes to
strengthen an angle.

{Angle meter}, an instrument for measuring angles, esp. for
ascertaining the dip of strata.

{Angle shaft} (Arch.), an enriched angle bead, often having a
capital or base, or both.

{Curvilineal angle}, one formed by two curved lines.

{External angles}, angles formed by the sides of any
right-lined figure, when the sides are produced or
lengthened.

{Facial angle}. See under {Facial}.

{Internal angles}, those which are within any right-lined
figure.

{Mixtilineal angle}, one formed by a right line with a curved
line.

{Oblique angle}, one acute or obtuse, in opposition to a
right angle.

{Obtuse angle}, one greater than a right angle, or more than
90[deg].

{Optic angle}. See under {Optic}.

{Rectilineal} or {Right-lined angle}, one formed by two right
lines.

{Right angle}, one formed by a right line falling on another
perpendicularly, or an angle of 90[deg] (measured by a
quarter circle).

{Solid angle}, the figure formed by the meeting of three or
more plane angles at one point.

{Spherical angle}, one made by the meeting of two arcs of
great circles, which mutually cut one another on the
surface of a globe or sphere.

{Visual angle}, the angle formed by two rays of light, or two
straight lines drawn from the extreme points of an object
to the center of the eye.

{For Angles of commutation}, {draught}, {incidence},
{reflection}, {refraction}, {position}, {repose}, {fraction},
see {Commutation}, {Draught}, {Incidence}, {Reflection},
{Refraction}, etc.