| lens clock | A device for measuring the radii of the curvature of a spectacle lens. Synonym: lens clock. Origin: Geneva, Switzerland (05 Mar 2000) |
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| biological clock | <biology, physiology> An internal biological mechanism which controls certain biological rhythms and biocycles, such as metabolism, sleep cycles, photosynthesis. (21 Mar 1998) |
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| circadian clock | <physiology> A biological timing mechanism that controls cell synchronisation (a entire population of cells divides simultaneously). (09 Oct 1997) |
| molecular clock | This term has two separate uses. 1. <molecular biology> The rate of fixation of mutations in DNA and thus times the rate of genetic diversification. 2. <cell biology> A biological system capable of maintaining up a timing rhythm or pulse. All such clocks are thought to be entrained by a natural oscillator such as the diurnal rhythm. (18 Nov 1997) |
| ten-o'clock | <botany> A plant, the star-of-Bethlehem. See Star. Source: Websters Dictionary (01 Mar 1998) |
| four-o'clock | 1. <botany> A plant of the genus Mirabilis. There are about half a dozen species, natives of the warmer parts of America. The common four-o'clock is M. Jalapa. Its flowers are white, yellow, and red, and open toward sunset, or earlier in cloudy weather; hence the name. It is also called marvel of Peru, and afternoon lady. 2. <zoology> The friar bird; so called from its cry, which resembles these words. Source: Websters Dictionary (01 Mar 1998) |
| achromatic lens | A compound lens made of two or more lens's having different indices of refraction, so correlated as to minimise chromatic aberration. (05 Mar 2000) |
| acoustic lens | In ultrasonography, a lens used to focus or diverge a sound beam; may be simulated by electronic manipulation of signals. (05 Mar 2000) |
| anterior pole of lens | The central point on the anterior surface of the lens of the eye. Synonym: polus anterior lentis. (05 Mar 2000) |
| anterior surface of lens | The anterior surface of the lens of the eye. Synonym: facies anterior lentis. (05 Mar 2000) |
| aplanatic lens | A lens designed to correct spherical aberration and coma (q.v.). Synonym: periscopic meniscus. (05 Mar 2000) |
| apochromatic lens | A compound lens designed to correct both spherical and chromatic aberrations. (05 Mar 2000) |
| asphenc lens | <physics> A lens made aplanatic by grinding the outer zones to a greater radius than the inner zones. Aplanatic condensers can be made in this way. A simple aspheric lens is widely used as a lamp condenser because of its efficiency in converging light rays to one focal plane. (05 Aug 1998) |
| aspheric lens | A lens with a paraboloidal surface that eliminates spherical aberration. (05 Mar 2000) |
| astigmatic lens | A lens in which one of the surfaces is curved in one meridian and less curved in the opposite meridian; e.g., a teaspoon or a football. Synonym: astigmatic lens. (05 Mar 2000) |
| axis of lens | A line connecting the anterior and posterior poles of the lens of the eye. Synonym: axis lentis. (05 Mar 2000) |