The Collaborative International Dictionary
Index \In"dex\, n.; pl. E. Indexes, L. Indices(?). [L.: cf. F. index. See Indicate, Diction.]
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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.
Tastes are the indexes of the different qualities of plants.
--Arbuthnot. 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.
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.
A prologue indicating what follows. [Obs.]
--Shak.(Anat.) The second finger, that next to the pollex (thumb), in the manus, or hand; the forefinger; index finger.
(Math.) The figure or letter which shows the power or root of a quantity; the exponent. [In this sense the plural is always indices.]
The ratio, or formula expressing the ratio, of one dimension of a thing to another dimension; as, the vertical index of the cranium.
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.
(computers) A file containing a table with the addresses of data items, arranged for rapid and convenient search for the addresses.
(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.
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(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.
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.
Wiktionary
n. (context physics English) The ratio of the speed of light in air or vacuum to that in another medium.
WordNet
n. the ratio of the velocity of light in a vacuum to that in a medium [syn: index of refraction]
Wikipedia
In optics, the refractive index or index of refraction n of a material is a dimensionless number that describes how light propagates through that medium. It is defined as
$$n = \frac{c}{v},$$
where c is the speed of light in vacuum and v is the phase velocity of light in the medium. For example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in a vacuum than it does in water.
The refractive index determines how much light is bent, or refracted, when entering a material. This is the first documented use of refractive indices and is described by Snell's law of refraction, n sinθ = n sinθ, where θ and θ are the angles of incidence and refraction, respectively, of a ray crossing the interface between two media with refractive indices n and n. The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as the critical angle for total internal reflection and Brewster's angle.
The refractive index can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is v = c/n, and similarly the wavelength in that medium is λ = λ/n, where λ is the wavelength of that light in vacuum. This implies that vacuum has a refractive index of 1, and that the frequency (f = v/λ) of the wave is not affected by the refractive index.
The refractive index varies with the wavelength of light. This is called dispersion and causes the splitting of white light into its constituent colors in prisms and rainbows, and chromatic aberration in lenses. Light propagation in absorbing materials can be described using a complex-valued refractive index. The imaginary part then handles the attenuation, while the real part accounts for refraction.
The concept of refractive index is widely used within the full electromagnetic spectrum, from X-rays to radio waves. It can also be used with wave phenomena such as sound. In this case the speed of sound is used instead of that of light and a reference medium other than vacuum must be chosen.
Usage examples of "refractive index".
But he had called for it to find, in its memory-banks, an organic compound of such-and-such a crystalline form, such-and-such a diffusion rate, such-and-such a specific gravity, and such-and-such a refractive index.
He placed a slide in the stage of a polarizing microscope, which, like Ray-Ban sunglasses, reduced glare, splitting light in different waves with different refractive index values to give us yet another clue as to the identity of the material.
But the essential phase was to place the transparent object whose refractive index was to be lowered between two radiating centres of a sort of ethereal vibration, of which I will tell you more fully later.
They all looked to where they suspected Nathan's spirit to be-out in the darkness of space where there was nothing whose refractive index Nathan could affect and become visible.
He took a drug which made his body of the same refractive index as air.
The refractive index of a transparent medium is a measure of light's being slowed down by successive forward re-emissions.
For instance, the refractive index of the lake fluid was very sensitive to the percentage of dissolved methane.
The exterior of the spire was optically pure and had die same refractive index as Telaria's atmosphere.
THE LIQUID'S REFRACTIVE INDEX, DENSITY, CONDUCTIVITY, AND GROSS CHEMICAL PROPERTIES ARE CONSISTENT WITH THOSE OF DEUTERIUM OXIDE CONTAINING A SMALL FRACTION OF MINERAL SOLVENTS.
Except really he was in Underhill Prime, usually called the trench, or Nadia's arcade, sitting on the upper balcony looking out at a dwarf sequoia, behind it the glass wall and the mirrors with their gradient refractive index that guided the light down into the concourse from its origin on the Cote D'Or.
A surface layer, two molecules thick, gave it a refractive index sensibly identical with that of air.
He computed the refractive index profile and determined that the light transmitting its waves through two of the strands inside a ribbon containing thousands of optic fibers was temporarily zigzagging at some point.