GEM 



GEM 



quarto ; "A preface to the Sciographia 

 of John Wells, of Brembridge, Esq." 

 1635, 8vo; "An Institution, trigonome- 

 trical, explaining- the doctrine of plane 

 and spherical Triangles, after the most 

 exact and compendious way, by Tables 

 of Sines,Tangents,&c. with the application 

 thereof to questions of Astronomy and 

 Navigation," 1634, octavo ; and after- 

 wards republished with enlargements by 

 William Leybourn, 1652, octavo; "An 

 Epitome of Navigation, with the neces- 

 sary tables," ikc.and "An Appendix con- 

 cerning the Use of the Quadrant, Fore- 

 staff, and Nocturnal," octavo ; " Oratio 

 in Laudem Gassendi Astronomic, habita 

 in Aula JEdis, Christi, Oxon ;" and of 

 several unpublished MSS. on the Doc- 

 trine of Eclipses, Lunar Astronomy, Ship 

 Building, &c. 



GEMINI, the Twins, in astronomy, one 

 of the twelve signs ot the zodiac, the third 

 in order, beginning with Aries. See 

 ASTRONOMY. 



GEMMA (RETNIEK), a learned Dutch 

 physician and mathematician in the six- 

 teenth century, was born at Dockum, in 

 Friesland, in the year 1508. He was edu- 

 cated to the medical science, of which he 

 became a professor in the university of 

 Louvain. But he WHS particularly eminent 

 for his proficiency in mathematics and 

 astronomy, which he taught with distin- 

 guished reputation, and the character of 

 being one of the best astronomers of his 

 time. The fame of his great scientific 

 knowledge, and of the excellent instru- 

 ments which he made use of in the illus- 

 tration of it, occasioned his being fre- 

 quently invited to the court of the Empe- 

 ror Charles V.; but he always modestly 

 declined the overtures made to him, pre- 

 ferring the tranquillity of his literary re- 

 treat to the honours which he might ex- 

 pect from princely favour. He died at 

 Louvain, in 1555, when only forty-seven 

 years of age. He has sometimes had the 

 surname of Friscius given him, from the 

 country in which he was born. The most 

 celebrated of his works were " Methodus 

 Artihroeticae ;" " De usu Annuli Astrono- 

 mici;" "De Locorum describendorum 

 Ratione, deque Distantiis eorum invenien- 

 dis ; " "Libellus de Principiis Astronomise 

 et Cosmographia," 8cc. " Demonstratio- 

 nes Geometric^ de usu Radii Astronomi- 

 ci," &.c. ; and De Astrolabio Catholico 

 Liber." 



The author had a son, named Corne- 

 lius, who was born at Louvain, in 1535, 

 and died in 1579. He was a poet, philo- 

 sopher, and physician, and taught the ma- 

 thematical sciences at Louvain with consi- 



VOL. V. 



derable reputation. He was the author of 

 " De Arte Cyclognomicx," &c. ; " De 

 Naturae divinis Characteristics, sen Cos- 

 mocritico ;" and " De Prodigiosa Specie 

 Naturaque Comets," occasioned by the 

 extraordinary new star in the constellation 

 Cassiopeia, in 1572, which disappeared 

 after being visible for eighteen months; 

 and other pieces. 



GEMMA, in botany, a bud, a compen- 

 dium of a plant seated upon the stem and 

 branches, and covered with scales, in or- 

 der to defend the tender rudiments in- 

 closed from cold, and other external inju- 

 ries, till, their parts being unfolded, they 

 acquire strength, and render any further 

 protection unnecessary. Buds, together 

 with bulbs, which are a species of buds, 

 generally seated upon or near the root, 

 constitute that part of the herb, by Lin- 

 na;us called hybernacula; that is, the win- 

 ter quarters of the future vegetable, as it 

 is during that severe season thai the ten- 

 der rudiments are protected in the man- 

 ner just mentioned. Plants, considered in 

 analogy to animals, may properly enough 

 be reckoned both viviparous and ovipa- 

 rous. Seeds are the vegetable eggs ; buds, 

 living foetuses, or infant plants, which re- 

 new the species as certainly as the seed. 

 In general, we may distinguish three 

 kinds of buds ; that containing the flow- 

 er, that containing the leaves, and that 

 containing both flower 'and leaves. The 

 first contains the rudiments of one or se- 

 veral flowers folded over one another, 

 and surrounded with scales. In several 

 trees, this kind of bud is commonly found 

 at the extremity of certain smallbranches, 

 which are shorter, rougher, and 'less gar- 

 nished with leaves than the rest. The ex- 

 ternal scales of this species of bud are 

 harder than the internal; both are fur- 

 nished with hairs, and in general more 

 swelled than those of the second sort. 

 The bud containing the flower, too, is 

 commonly thicker, shorter, almost square, 

 less uniform, and less pointed, being ge- 

 nerally terminated obtusely. The second 

 species of bud contains the rudiments of 

 several leaves which are variously folded 

 over one another, and outwardly sur- 

 rounded by scales, from which the small 

 stipulse that are seated at the foot of the 

 young branches are chiefly produced. 

 These buds are commonly more pointed 

 than the former sort. In the hazle-nut, 

 however, they are perfectly round; and 

 in horse-chesnut very thick. The third 

 sort of bud is smaller than either of the 

 preceding, and produces both flowers and 

 leaves,though not always in the same man- 

 ner. Sometimes the flowers and leaves 



