SPECTACLES

n. Spe2kt'a3-k'lz. From spectaculum, a show. Lat., cons pic ill a. Fr., lunettes. Ger., Brillen. Gla es or lenses to a ist or improve sight. [F.] Decentred s. Lenses devised by Giraud-Teulon, so constructed that the eccentric portions of two convex lenses are used instead of the centre; they thus acquire a slightly prismatic action. IF.] Mica s. S. made of mica invented by Cohn, to be used as eye-protectors in place of those made of gla and wire-gauze. [F.] Orthoscopic s. Of Scheffler, lenses cut out from,the periphery of a large lens so as to act as decentred lenses. [FJ Pantoscopic s. Ger., Mallerbrillen. Lenses having different foci in their upper and lower parts; first employed by Franklin. [F.] Periscopic s. See Periscopic GLASSES.- Prismatic s. S. having prisms with bases so arranged that overstrain of an ocular muscle is relieved, [a, 34.] Snow s. A kind of s. used in high latitudes, as a protector against the glare of the snow; usually made of very light wood, with a narrow slit for the pa age of light. [F.] Stenopaeic s. S. consisting of an oval metal plate having a small central aperture that permits the pa age of only the central rays that fall in the optic axis, [a, 34.] Turn-pin temple s. Spectacle-frames in which the wings are jointed and the end pieces turned down behind the ears, giving the gla es a firmer support. [F.] [s. 510]