refraction

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The turning or bending of any wave, such as a light or sound wave, when it passes from one medium into another of different optical density.
• noun Astronomy The apparent change in position of a celestial object caused by the bending of light rays as they enter Earth's atmosphere.
• noun The ability of the eye to bend light so that an image is focused on the retina.
• noun Determination of this ability in an eye.

from The Century Dictionary.

• noun The act of refracting, or the state of being refracted: almost exclusively restricted to physics, and applied to a deflection or change of direction of rays, as of light, heat, or sound, which are obliquely incident upon and pass through a smooth surface bounding two media not homogeneous, as air and water, or of rays which traverse a medium the density of which is not uniform, as the atmosphere.
• noun In logic, the relation of the Theophrastian moods to the direct moods of the first figure.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act of refracting, or the state of being refracted.
• noun 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.
• noun 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.
• noun 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.
• noun (Opt.) the angle which a refracted ray makes with the perpendicular to the surface separating the two media traversed by the ray.
• noun (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.
• noun (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.
• noun (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.
• noun See under Index.
• noun (Opt.) an instrument provided with a graduated circle for the measurement of refraction.
• noun etc., the change in the apparent latitude, longitude, etc., of a heavenly body, due to the effect of atmospheric refraction.
• noun 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics The turning or bending of any wave, such as a light or sound wave, when it passes from one medium into another of different optical density.
• noun metallurgy The degree to which a metal or compound can withstand heat

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the change in direction of a propagating wave (light or sound) when passing from one medium to another
• noun the amount by which a propagating wave is bent