折射率

[ noun ]
the ratio of the velocity of light in a vacuum to that in a medium
<noun.linkdef>

Index \In"dex\, n.; pl. E. {Indexes}, L. {Indices}(?). [L.: cf.
F. index. See {Indicate}, {Diction}.]
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.

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.

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.
[1913 Webster +PJC]

4. A prologue indicating what follows. [Obs.] --Shak.

5. (Anat.) The second finger, that next to the pollex
(thumb), in the manus, or hand; the forefinger; {index
finger}.

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}.]

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.


Refractive \Re*fract"ive\ (r?*fr?kt"?v), a. [Cf. F.
r['e]fractif. 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.