VEX 



[456 ] 



VOL 



but little from a cube, and is divi- 

 sible into triangular prisms, for the 

 integrant particles. It yields to 

 cleavage readily, parallel to all its 

 planes, with sufficient brilliancy to 

 obtain incidences of 90' by the 

 reflective goniometer in every di- 

 rection. Haiiy has described eight 

 modifications of its primitive form. 

 It is somewhat harder than quartz. 

 Specific gravity from 3 '2 to 3-4. 

 It is often translucent, sometimes 

 transparent, and sometimes nearly 

 or quite opaque. It possesses dou- 

 ble refraction. Fracture uneven, 

 inclining to small conchoidal. Be- 

 fore the blow-pipe, it fuses easily 

 into a yellowish translucent glass, 

 which afterwards becomes black. 

 Its constituents vary, in some de- 

 gree, according to the localityjwhence 

 it has been obtained. Klaproth 

 obtained from a specimen from the 

 neighbourhood of Vesuvius, silex 

 35-50, lime 33-00, alumine 22-2, 

 oxide of iron 7-50, oxide of manga- 

 nese 0'25. It is found abundantly 

 in the vicinity of Mount Vesuvius, 

 in the ejected masses, where its 

 crystals line the cavities of volcanic 

 rocks, accompanied by garnet, horn- 

 blende, melanite, mica, and icespar, 

 from which circumstance it has 

 obtained its name, and in primary 

 rocks in Ireland, Scotland, and 

 other parts of Europe. 

 VEXI'LLTJM. i (vexillum, a standard, or 

 VE'XIL. j banner, Lat.) In bo- 

 tany, the upper large petal of a 

 papilionaceous flower. 

 VI'LLI. (from viUus, a hair, Lat.) 



1. In anatomy, fine small fibres, 

 resembling a covering of down. 



2. In botany, fine downy hairs, 

 covering fruits, flowers, and plants. 



VI'LLOTTS. (villosm, Lat.) Downy; 



pubescent; shaggy. 

 VIO'LET QUARTZ. See Amethyst. 

 VI'SCID. } (viscidus, Lat.) Glutinous; 

 Vi'scous. ) tenacious; clammy. 

 Vi'scus. (yiseus, Lat.) In the plural, 



viscera ; this term is generally ap- 



plied to the organs connected with 

 digestion; sometimes to the bowels 

 only. Any organ of the body may 

 be denominated a viscus. 

 VI'TREOUS. (vitreus, Lat.) Glassy; 

 resembling glass. 



1. In mineralogy, a term used to 

 denote a particular lustre of some 

 minerals, resembling that of glass. 



2. In anatomy, a term applied to 

 one of the humours of the eye. 

 The vitreous humour occupies more 

 than three-fourths of the globe of 

 the eye ; it is contained in an ex- 

 ceedingly delicate texture of cellular 

 substance, and is situated behind 

 the crystalline lens. 



VI'TREOUS SAND TUBES. See Fulgorite. 



VI'VIANITE. The Vivianit of Werner ; 

 the Per Phospate of Haiiy. Phos- 

 phate of iron. A mineral of a green 

 or blue colour. Its constituents 

 are, protoxide of iron 47 -5, phos- 

 phoric acid 32, water 20. 



VIVI'PAEOUS. (viviparus, Lat. from 

 vivus, alive, and pario, to bring 

 forth; vivipare, Fr.) Animals are 

 termed viviparous in which no egg, 

 properly so called, is formed, but 

 bring forth their young alive and 

 perfect. 



VOLCA'HTC PRODUCTIONS. These are 

 numerous and diversified. Lava, 

 scoria, enamel, and glass, comprise 

 by far the most important and 

 interesting volcanic productions. 

 The different states of lava, whether 

 vitreous, compact, or scoriaceous, 

 depend on the different circum- 

 stances under which it has cooled. 

 Aqueous vapour is in general very 

 abundant. Volcanic products are 

 naturally divisible into two great 

 classes; sub-aerial, and sub-aque- 

 ous. The first, being in many 

 respects open to our investigation, 

 is to a considerable extent under- 

 stood. The second, for the most 

 part hidden from examination, is 

 necessarily but little known, though 

 recent observation has thrown some 

 light upon it. " Various classifi- 



