| crown glass | A compound of lime, potash, alumina, and silica; commonly used in lenses; has a low dispersion (52.2) relative to index of refraction (1.523). (05 Mar 2000) |
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| cupping glass | A glass vessel, from which the air has been exhausted by heat or a special suction apparatus, formerly applied to the skin in order to draw blood to the surface. See: cupping, cup. Synonym: cup. (05 Mar 2000) |
| half-glass spectacles | Spectacles, used for reading, in which the upper portion of the lenses are removed. Synonym: clerical spectacles, pantoscopic spectacles, pulpit spectacles. (05 Mar 2000) |
| soluble glass | A silicate of potassium or sodium, soluble in hot water but solid at ordinary temperatures; used for fixed dressings. Synonym: water glass. (05 Mar 2000) |
| quartz glass | A transparent, colourless crystal, made by fusing pure quartz sand, which transmits ultraviolet light. (05 Mar 2000) |
| object glass | 1. <psychology> Perceptible to the external senses. 2. <ophthalmology> The lens or system of lenses in a microscope (or telescope) that is nearest to the object under examination. Origin: L. Objectivus (18 Nov 1997) |
| opera-glass hand | A deformity of the hand seen in chronic absorptive arthritis, the fingers and wrists being shortened and the covering skin wrinkled into transverse folds; the phalanges appear to be retracted into one another like an opera glass or miniature telescope. Synonym: main en lorgnette. (05 Mar 2000) |
| three-glass test | The bladder is emptied by passing urine into a series of 3-ounce test tubes, and the contents of the first and the last are examined; the first tube contains the washings from the anterior urethra, the second, material from the bladder, and the last, material from the posterior urethra, prostate, and seminal vesicles. Synonym: Valentine's test. (05 Mar 2000) |
| two-glass test | The urine, in a case of gonorrhoea, is passed into two glasses; if the gonococci and gonorrhoeal threads are found only in the first glass the probability is that the process is limited to the anterior urethra. Synonym: two-glass test. (05 Mar 2000) |
| flint glass | <chemistry> A soft, heavy, brilliant glass, consisting essentially of a silicate of lead and potassium. It is used for tableware, and for optical instruments, as prisms, its density giving a high degree of dispersive power; so called, because formerly the silica was obtained from pulverized flints. Synonym: crystal glass. Cf. Glass. The concave or diverging half on an achromatic lens is usually made of flint glass. Source: Websters Dictionary (01 Mar 1998) |
| lady's looking-glass | <botany> See Venus's looking-glass, under Venus. Source: Websters Dictionary (01 Mar 1998) |
| focusing glass | <microscopy> A hand magnifier, used at the focal plane of a camera, usually with the ground glass removed. Its purpose is to examine the image for critical focus. It is, as a rule, a low-power magnifier so mounted that it is in focus when supported on a piece of clear glass at the focal plane of the cam- era, for studying the image. It operates equally well on the aerial image. (05 Aug 1998) |