GIB 



GL A 



GEO'RGIUM SIDUS. The name 

 given by Herschel to the planet dis- 

 covered by himself in 1781 ; it is, how- 

 ever, more generally knov*rn by the name 

 of its discoverer, or by that of Uranus. 



GE'OTHERMO'METER (7?), the 

 earth, thermometer). An instrument in- 

 vented by Magnus, for measuring the 

 degree of terrestrial heat at different 

 places, especially in mines and Artesian 

 wells. The temperature appears to rise 

 1° F. for every 60 or 70 feet of descent 

 below the surface ; hence, at a depth of a 

 few miles, the earth must be in a state of 

 incandescence. 



GERANIA'CE^. The Geranium tribe 

 of Dicotyledonous plants. Herbaceous 

 plants or shrubs, with stems tumid and 

 separable at the joints; stamens mona- 

 delphous ; fruit composed of five cocci, 

 each terminated by an indurated style, 

 consolidated round a long beak -like axis, 

 from which they separate with elasticity, 

 when ripe, by the rolling back of the 

 styles. 



GERMAN SILVER. Packfong. A 

 white alloy of nickel, formed by fusing 

 together 100 parts of copper, 60 of zinc, 

 and 40 of nickel. 



GE'RMEN. The term, applied by 

 Linnaeus to the ovary of plants, or the 

 hollow case forming the base of the pistil, 

 enclosing the ovules, and always contain- 

 ing one or more cells or cavities. 



GERMINA'TION {germino, to bud). 

 A term applied by botanists to that func- 

 tion by which the embryo contained in 

 the seed is first called into life. 



GEY'SER. A boiling fountain in Ice- 

 land, which frequently throws out its 

 contents to the height of more than a 

 hundred feet, sometimes to thrice that 

 elevation. 



GIANTS' CAUSEWAY. A columnar 

 basaltic formation on the northern coast 

 of Antrim in Ireland, connected with a 

 trap district which occupies almost the 

 whole of the county, &c., comprehending 

 an area of about 800 square miles on both 

 sides of the valley of the Bann. 



GI'BBOUS {gibbus, protuberant). 

 Humped ; a term applied to the convex- 

 ity of a solid body, and used in reference 

 to the enlightened parts of the moon, 

 whilst she is moving from her first 

 quarter to the full, and from the full to 

 the last quarter. In Zoology, any part 

 of a shell more particularly elevated 

 above the surface, or unusually so in 

 comparison with other species, is termed 

 gibbous, as in strombus gibbosus. 

 151 



GIE'SECKITE. A granular mineral 

 brought from Greenland by Sir C. 

 Giesecke. 



GI'NGLYMOID (y^^YXuiuof, a hinge, 

 et6o9, likeness). Hinge-like ; a term ap- 

 plied to a joint formed for motion on one 

 plane. 



GFRASOL. A term derived from the 

 Italian giro-sole, or turn-sun, and applied 

 to a milk-white or bluish opal, which 

 reflects a reddish colour when turned to 

 the sun. The term has been corrupted 

 into Jerusalem, as applied to a species of 

 sunflower, the helianthus tuberosus, vul- 

 garly said to turn its flowers to the sun. 



GLA'CIAL ACID [glacies, ice). The 

 strongest acetic acid which can be pro- 

 duced. It exists in a crystallized state 

 under 50° Fahr., and contains 7d percent, 

 of real acid. 



GLA'CIER {glace, ice). An accu- 

 mulation of ice and hardened snow, 

 occurring in the valleys and on the slopes 

 of the Alps and other lofty mountains. 

 Saussure distinguishes two kinds of gla- 

 cier ; viz. those contained in the valleys 

 more or less deep, and which, though at 

 great elevations, are still commanded on 

 all sides by mountains higher still ; and 

 those not contained in the valleys, but 

 spread out on the slopes of the higher 

 peaks. See Moraine. 



GLA'CIS. A term borrowed from the 

 language of fortification, in which it de- 

 notes an easy insensible slope or decliv- 

 ity, less steep than that of a talus. 



GLAI'RINE. A term referred by some 

 to a gelatinous vegetable matter ; by 

 others to a pseud-organic substance 

 formed on thermal waters. 



GLANCE {glanz, splendour). A de- 

 signation of certain minerals which have 

 a metallic or pseudo-metallic lustre, as 

 glance-coal, lead-glance, &c. 



GLANCE-COAL. Anthracite. A va- 

 riety of coal which burns without flame 

 or smell. It occurs in beds in clay-slate, 

 greywacke, and alum-slate, but most 

 abundantly in secondary rocks, as in coal 

 and trap formations. Slaty glance-coal 

 is another variety, called in this country 

 blind coal. A third variety occurs in 

 basaltic columnar rows, near Cumnock 

 in Ayrshire, 



GLAND {glans, an acorn). In Botany, 

 a small mass of firm cellular tissue, 

 which is often much harder and more 

 coloured than that which surrounds it. 

 It may be simple or compound, stalked 

 or sessile. Glands are termed utricular, 

 when they appear as elevated, distended 

 H4 



