Eyepiece

( Optics.) An eye-piece, or power, as it is sometimes called, is the lens or combination of lenses used in microscopes or telescopes to examine the aerial image formed at the focus of the object-gla . The ordinary eye-piece is a combination, and may be either positive or negative. The former consists of two planoconvex lenses, with their convex sides towards each other; and is used for micrometers. The negative, or Huygenian, consists of the same lenses with the convex sides turned away from the eye. Besides these there are in use, for observations of the sun, a diagonal eye- piece, in which a very small percentage of the sun's light and heat is reflected from the first surface of a prism, the rest being transmitted; and Dawes ' solar eye-piece, in which the light is reduced by observing only an extremely minute portion of the solar surface. Steinheil and Kellner have also contrived eye-pieces; they, however, are not in such general use. The eye-piece of opera-gla es consists of a combination of bi-concave lenses-an arrangement which is almost out of date as applied to telescopes, although occasionally it may be used with advantage. - All these eye-pieces, except the last-mentioned, invert. The terrestrial or erecting eyepiece is a combination of four lenses, used for terrestrial telescopes. Eye'-salve, ( -sav ,) n. Ointment for the eye. Eye'-service, n . Service performed only under the inspection or the eve of an employer. Eyer's Grove, in Pennsylvania , a P.O. of Columbia co. Eye's ight, n. The sight of the eye; view; observation; the sense of seeing.