CRY 



CUB 



no nervous filaments or masses have been 

 discovered. They correspond Avith the 

 Acrita of Macleay, and the Protozoa and 

 Oozoa of other writers. 



CRY'STAL (Kp.'/o-TaWof, ice). A solid 

 body of a limited symmetrical form, in- 

 cluded by plane surfaces. In organized 

 bodies spherical forms predominate, whilst 

 unorganized bodies are mostly angular. 

 Quartz, being often found in a crystalline 

 form, and being transparent like ice, was 

 called rock-crystal ; and hence all other 

 minerals of regular forms are called 

 crystals, whether they be clear or opaque. 



1. The structure of a crystal is the 

 arrangement of its component parts, and 

 this is ascertained by splitting it in the 

 direction of its planes of cleavage ; the 

 crystal is thus obtained in its primitive 

 form, and, when this differs from the 

 figure at first presented by the body, the 

 latter is called the secondary form. 



2. Primitive Forms. By the term 

 "primitive form," Haiiy designates the 

 nucleus of crystals ; " secondary forms" 

 are varieties which differ from the primi- 

 tive form. The primitive forms of crys- 

 tals are the tetrahedron, the parallelopi- 

 pedon, the octohedron, the hexagonal 

 prism, the rhombic dodecahedron, and 

 the dodecahedron with triangular faces. 

 To the parallelopipedon belong the cube 

 and the rhombohedron. 



3. The angles at which the edges of 

 the planes or faces of a crystal meet, are 

 called plane angles ; and the point formed 

 by the union of three or more of these, a 

 solid angle. The lines which join these 

 points, and pass through the middle of 

 the crystal, are called its axes ; there are 

 usually three of these, a principal axis, 

 and two secondary or subordinate axes. 



4. In the Weriierian language of crys- 

 tallization, the following terms are em- 

 ployed : — "When a secondary form differs 

 from the cube, the octohedron, &c., only 

 in having several of its angles or edges 

 replaced by a face, this change of the 

 geometrical form is called a truncation. 

 The alteration in the principal form pro- 

 duced by two new faces inclined to one 

 another, and which replace, by a kind of 

 bevel, an angle or an edge, is called a 

 hevelment. When these new faces are to 

 the number of three or more, they pro- 

 duce what Wea-ner termed a pointing or 

 acumination. When two faces unite by 

 an edge in the manner of a roof, they 

 have been called culmination. The term 



I replacement is occasionally used for bevel- 



ment. 

 !; 95 



CRYSTAL ELECTRICITY. A term 



sometimes applied to thermo-electric polar 

 tension, from its being displayed princi- 

 pally in crystallized substances, especially 

 in those which belong to the mineral 

 kingdom. The crystals which exhibit 

 this property are termed thermo-electric 

 crystals, as tourmaline. 



CRYSTALLINE LENS. A thick com- 

 pact humour, in form of a flattish convex 

 lens, situated in the middle of the eye, 

 and causing that refraction of the rays of 

 light which is necessary to make them 

 meet in the retina, and form an image 

 thereon, whereby vision is performed. 



CRYSTALLIZA'TION (KpvaraWo?, a 

 crystal). The process by which the par- 

 ticles of liquid or gaseous bodies form 

 themselves into crystals, or solid bodies 

 of a regularly limited form. 



Crystallization, Alternate. This term 

 is applied to a phenomenon which takes 

 place when several crystallizable sub- 

 stances, having little attraction for each 

 other, are present in the same solution. 

 That which is largest in quantity and 

 least soluble crystallizes first, in part; 

 the least soluble substance next in quan- 

 tity then begins to separate ; and thus 

 different substances, as salts, are often 

 deposited in successive layers from the 

 same solution. 



CRYSTALLO'GRAPHY (KpvaTaWo^, 

 a crystal, ypd^w, to describe). The science 

 which investigates the relation of crys- 

 talline forms, and the origin and struc- 

 ture of crystals. 



CTE'NOBRANCHIA'TA {ktcU, a 

 comb, /3pa7X'ci» giJ^s). A term synony- 

 mous with Pectinibranchiata, applied to 

 an order of Gasteropods which breathe 

 by means of pectinated gills. 



CTENOI'DES (KTeif, a comb, cZaor, 

 likeness). An order of fishes, furnished 

 with scales composed of layers with pec- 

 tinated or toothed posterior margins. 



CU'BATURE. The measurement of 

 the contents of a solid body, or the find- 

 ing a cube equal to it. 



CUBE (ku/3o9, acube). A geometrical 

 solid, contained by six equal squares. It 

 is the measuring unit of solid content, as 

 the square is that of superficial extent, 

 or area. 



CUBE ORE. Hexahedral Olivenite, 

 or Wurfelerz ; a green mineral, which 

 occurs crystallized in a perfect cube, 

 in Cornish mines, accompanied with 

 iron-shot quartz. It is an arseniate of 

 iron. 

 CUBIC EQUATION. An equation 



