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index of refraction
(encz) | index of refraction,index lomu [fyz.] |
Index of refraction
(gcide) | Index \In"dex\, n.; pl. E. Indexes, L. Indices(?). [L.: cf.
F. index. See Indicate, Diction.]
[1913 Webster]
1. That which points out; that which shows, indicates,
manifests, or discloses; as, the increasing unemployment
rate is an index of how much the economy has slowed.
[1913 Webster +PJC]
Tastes are the indexes of the different qualities of
plants. --Arbuthnot.
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2. That which guides, points out, informs, or directs; a
pointer or a hand that directs to anything, as the hand of
a watch, a movable finger or other form of pointer on a
gauge, scale, or other graduated instrument. In
(printing), a sign [[hand]] (called also fist) used to
direct particular attention to a note or paragraph.
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3. A table for facilitating reference to topics, names, and
the like, in a book, usually giving the page on which a
particular word or topic may be found; -- usually
alphabetical in arrangement, and printed at the end of the
volume. Typically found only in non-fiction books.
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4. A prologue indicating what follows. [Obs.] --Shak.
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5. (Anat.) The second finger, that next to the pollex
(thumb), in the manus, or hand; the forefinger; {index
finger}.
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6. (Math.) The figure or letter which shows the power or root
of a quantity; the exponent. [In this sense the plural is
always indices.]
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7. The ratio, or formula expressing the ratio, of one
dimension of a thing to another dimension; as, the
vertical index of the cranium.
[Webster 1913 Suppl.]
8. A number providing a measure of some quantity derived by a
formula, usually a form of averaging, from multiple
quantities; -- used mostly in economics; as, the index of
leading indicators; the index of industrial production;
the consumer price index. See, for example, the {consumer
price index}.
[PJC]
9. (computers) A file containing a table with the addresses
of data items, arranged for rapid and convenient search
for the addresses.
[PJC]
10. (computers) A number which serves as a label for a data
item and also represents the address of a data item
within a table or array.
[PJC]
11. (R. C. Ch.), The Index prohibitorius, a catalogue of
books which are forbidden by the church to be read; also
called Index of forbidden books and {Index Librorum
Prohibitorum}.
[PJC]
Index error, the error in the reading of a mathematical
instrument arising from the zero of the index not being in
complete adjustment with that of the limb, or with its
theoretically perfect position in the instrument; a
correction to be applied to the instrument readings equal
to the error of the zero adjustment.
Index expurgatorius. [L.] See Index prohibitorius
(below).
Index finger. See Index, 5.
Index glass, the mirror on the index of a quadrant,
sextant, etc.
Index hand, the pointer or hand of a clock, watch, or other
registering machine; a hand that points to something.
Index of a logarithm (Math.), the integral part of the
logarithm, and always one less than the number of integral
figures in the given number. It is also called the
characteristic.
Index of refraction, or Refractive index (Opt.), the
number which expresses the ratio of the sine of the angle
of incidence to the sine of the angle of refraction. Thus
the index of refraction for sulphur is 2, because, when
light passes out of air into sulphur, the sine of the
angle of incidence is double the sine of the angle of
refraction.
Index plate, a graduated circular plate, or one with
circular rows of holes differently spaced; used in
machines for graduating circles, cutting gear teeth, etc.
Index prohibitorius [L.], or Prohibitory index (R. C.
Ch.), a catalogue of books which are forbidden by the
church to be read; the index expurgatorius [L.], or
expurgatory index, is a catalogue of books from which
passages marked as against faith or morals must be removed
before Catholics can read them. These catalogues are
published with additions, from time to time, by the
Congregation of the Index, composed of cardinals,
theologians, etc., under the sanction of the pope. --Hook.
Index rerum [L.], a tabulated and alphabetized notebook,
for systematic preservation of items, quotations, etc.
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Index of refraction
(gcide) | 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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index of refraction
(wn) | index of refraction
n 1: the ratio of the velocity of light in a vacuum to that in a
medium [syn: refractive index, index of refraction] |
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