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.
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 on a gauge, scale, or other graduated
instrument. In printing, a sign [☞] used to direct particular
attention to a note or paragraph; -- called also
3. A table for facilitating reference to
topics, names, and the like, in a book; -- usually alphabetical in
arrangement, and printed at the end of the volume.
4. A prologue indicating what follows.
5. (Anat.) The second digit, that next
to the pollex, in the manus, or hand; the forefinger; index
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.]
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,