aperture

[In Sp. & Port. abertura; Ital. apertura. From Lat. apertura.] A. Ordinary Language: I. & II. The act of opening; the state of being opened. 1. In a literal sense: 2. Figuratively. Spec ., explanation. "It is too much untwisted by the doctors, and, like philosophy, made intricate by by explications, and difficult by the aperture and di olution of distinctions. -Taylor. III. A thing or place opened; an opening, a hole. 1. Literally : 2. Figuratively : and to him who treads Rome for the sake of ages, Glory sheds Her light through thy sole aperture." B. Technically: Byron: Childe Harold, iv. 148. 1. Anatomy , Zoology , Botany , dc.: (a) The aperture of a univalve shell is the opening or mouth. In molluscs which feed on vegetable matter it is entire; while in those which are animal feeders it has a notch or canal. In some families it has an operculum or cover. The margin of the aperture is called the peristome. (Woodward: Mollusca , 1st ed., 1851, p. 101.) (b) Any other opening. the hack aperture of the nostril a."-Owen: Cla if. of Mammal., p. 29. 2. Optics: The diameter of the object-gla of a refracting telescope, or the speculum or mirror of a reflector. The larger the aperture (i.e., the area of the surface through which the light is transmitted, or from which it is reflected), the greater is the power of the telescope to penetrate into space and consequently bear higher magnifying powers. The apertures of Sir W. Herschel's celebrated reflecting telescopes were 7, 12, 18, and 48 inches; while those of the Earl of Ro e are 3 and 6 feet. Very powerful refracting telescopes with large apertures have been recently constructed, that at the Lick Observatory being 36 inches, while still larger ones are projected. Within the last few years silvered gla parabolic mirrore of the Newton i an form have been constructed with large apertures and short focal length, thus rendering these instruments exceedingly convenient for Sir W. Herschel's 18-inch metallic speculum, used for examining the nebulæ and Milky Way, had a focal length of 20 feet; modern telescopes, with silvered-gla mirrors, have been constructed of the same aperture, but with a focal length of not more than 7 feet. Thus a larger aperture is now a more valuable feature in a telescope than great focal length, the unwieldy tubes formerly used being entirely dispensed with. use. Aperture ' always means the clear space which receives the light of the object; the diameter of the object gla in a chromatics, or the large speculum in reflectors, exclusive of its setting."-Webb: Celestiol Objects , 3rd ed. (1873), p. 1. Angular aperture (in microscopes): The amount of light transmitted by the objective, and consequently the distinctne of the image afterwards magnified by the lenses forming the eye-piece When an objective of the largest angular aperture is employed, the more delicate markings of the object under examination, invisible when objectives of le angular aperture are used, are seen with great distinctne . [OBJECTIVE.] 3. Geom .: The space between two right lines which meet in a point and form an angle. āp'-er-ỹ, s. [Eng. aper ; -y.] An aping; servile imitation. (Cole ridge.)