Re-frac'tion, n.

n. [Fr. réfraction, Sp. refracción, It. rifrazione, Pr. refraccio. See supra.]

1. The act of refracting, or the state of being refracted.
2. (Opt.) The change in the direction of a 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.

Refraction out of a rarer medium into a denser, is made toward the perpendicular. Newton. 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 to be deducted from the apparent altitude of a heavenly body on account of atmospheric refraction, in order to obtain the true altitude. Refraction. a b, vessel, lower part filled with water; s l, ray of light in straight line; r p s, ray of light refracted; Q q, perpendicular. Conical refraction, the refraction of a ray of light into an infinite number of rays, forming a hollow cone—a phenomenon which occurs when a ray of light is passed through crystals of some substances, under certain circumstances. It 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 William R. Hamilton by mathematical reasoning alone, unaided by experiment. Nichol. — Double refraction, the refraction of light in two directions, and consequent production of two distinct images. The power of double refraction is possessed by all crystals, except those of the tesseral or regular system. Dana. — Index of refraction. See INDEX. — Refraction of latitude, longitude, declination, right ascension, &c., the change in the latitude, longitude, &c., 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.