Ocular

(ok' -u-lar). I. Pertaining to the eye. 2. An optic combination that refracts the diverging rays forming the real object-image so that they may pa through the pupil of the observer's eye; the eye-piece of a compound miscroscope. Like the simple microscope, it also forms a virtual or magnified image of the real image. O., Campani's. See O., Huygenian. O. Cleft. See Cleft . O., Compensating, an ocular specially constructed for use with the apochromatic objective. It serves to correct or compensate for aberrations in the objective outside the axis. O. Cup. See Optic . O., Erecting, one that is provided with an erecting prism and gives an erect image of the object. O., Huygenian, one that consists of two plano-convex lenses, the convexities being directed toward the objective. The lower and larger lens is the field-lens; the upper and smaller is the eye-lens. O., Kellner's. See O., Orthoscopic. O., Micrometer, is an ocular with which is connected a micrometer for the purpose of measuring the real image of the object. O. Micrometer Ratio. See Ratio . O. Muscles, External, the six muscles moving the globe of the eye. See Muscles, Table of. O. Muscles, Internal, the ciliary muscle and the iris. O., Negative, an ocular in which the real image formed by the objective lies somewhere between the two lenses or lens systems forming the ocular. O., Orthoscopic, one that consists of a bi-convex field-gla and an achromatic double meniscus (bi-convex and bi-concave) eye-lens. Os., Parfocal, oculars of different powers which may be interchanged without putting the image wholly out of focus. O., Periscopic; a positive ocular devised by Gundlach; it has a double convex field-lens and a triplet eye-lens. O., Positive, one through which the real image is formed outside of the ocular, and is magnified by the entire system of ocular lenses like a simple microscope. O., Projection, an ocular especially designed for projecting the image formed by an objective on a screen for cla -demonstration, or for photography. O., Ramsden's, an ocular consisting of two plano-convex lenses with their convex surfaces facing each other. It has been used in micrometry. O., Searching, an ocular of low power used for finding an object. It consists of a single field-lens and a double eye -lens. O.