CRY 



CUB 



The cube, fig 15, or solid, composed of 

 six quadrilateral planes united at right 

 angles. 4th. The rhomb, fig. 16, or solid, 

 of six quadrilateral planes united at ob- 

 lique angles. 5th. The prism, or solfd, 

 of two terminal planes, parallel, equal, 

 and similar, connected by quadrangular 

 lateral planes, having one direction ; the 

 number of lateral planes may of course 

 be various ; the usual form observed in 

 crystals are, the four-sided rectangular 

 prism, fig. 17 ; and the six-sided equian- 

 gular prism, fig. 19. 6th. The pyramid, 

 or solid, the base of which is a plane of 

 an indeterminate number of sides, and 

 the sides triangles, the vertices of which 

 meet in one point, forming the summit : 

 the more common varieties of this figure, 

 as forms of crystals, are the three-sided 

 pyramid, or tetraedron, fig. 20, and the 

 four-sided pyramid, fig. 21. 7th. The ta- 

 ble, which, strictly speaking, is nothing 

 but a very compressed prism ; it is de- 

 fined as composed of two parallel lateral 

 planes and of an intermediate number of 

 terminal planes, connected with the late- 

 ral planes and with each other, and small, 

 compared with the lateral ones ; the prin- 

 cipal varieties are, the oblique-angular, 

 or rhomboidal four-sided table, fig. 23, 

 the rectangular four- sided table, fig. 24, 

 and the six-sided table, fig. 24. Lastly, 

 The lens, fig. 25, a solid, consisting only 

 of two planes which are curved, of which 

 there are two varieties, one composed of 

 two convex planes, and another compos- 

 ed of a convex and a concave plane. 

 These simple figures are modified by 

 combination, by truncation, by bevel- 

 ment, and by acumination. 



The modifications by combination are 

 confined to the pyramids, and these are 

 frequent, two pyramids being joined by 

 the base ; the lateral planes of the one 

 being set either directly on the lateral 

 planes of the other, as in the double four- 

 sided pyramid, or octaedron, fig. 26, or 

 obliquely, us in the double four-sided py- 

 ramid, fig. 27. Fig. 28, is the double six- 

 sided pyramid. 



A crystal is said to be truncated, when 

 any or all of its solid angles or edges ap- 

 pear cut off,so that where there would have 

 been an edge or angle we have a plane, 

 as has already been represented in fig. 

 2 and 3. These two figures represent 

 forms arising from the truncation of the 

 cube : fig. 29, shews the cube with the 

 angles and edges truncated : fig. 30, the 

 six-sided prism, with truncated termi- 

 Tial edges : fig .til, the same prism, with 

 both the lateral and terminal edges trun- 

 cated. 



A crystal is said to be bevelled, when 

 its edges, angles, or terminal planes, are so 

 altered, that instead of an angle edge or 

 terminal plane, there appear two smaller 

 converging plunes, which terminate in 

 an edge : fig. " 32, shews the cube with 

 bevelled edges : fig. 33, the three-sided 

 pyramid with bevelled edges : fig. 34, 

 the oblique four-sided prism, bevelled on 

 both extremities. 



Lastly, the forms of crystals are altered 

 by acumination. This is that kind of al- 

 teration, in which, in place of the angles 

 or terminal planes of a crystal, there are 

 three or more planes converging, and 

 forming a point or edge : fig. 35, shews 

 the cube, with angles acuminated by 

 three planes set on the lateral planes ; fig. 

 36, the rectangular four-sided prism, acu- 

 minated by four planes set on the lateral 

 planes : fig. 37, the six-sided prism, acu- 

 minated by six planes set on the lateral 

 planes. This kind of modification is often 

 described as consisting of the primary 

 form, with pyramidal terminations. 



The forms of crystals from the preced- 

 ing modifications are frequently still more 

 altered, and rendered complicated, by 

 being super-added and combined; and 

 by the extent of the modifications, one 

 form frequently passes into another. The 

 figures of crystals are likewise rendered 

 complicated by aggregation, two or more 

 crystals of the same substance being 

 more or less closely united. 



For the more minute details of this sub- 

 ject, particularly asrelatnig to mineralogy, 

 reference may be had to Weaver's trans- 

 lation of the " External Characters of 

 Minerals," by Werner; or the treatise on 

 the same subject by Professor Jameson. 

 See CRYSTALLIZATION. 



CRYTANDRA, in botany, a genus of 

 the Pentandria Monogynia class and or- 

 der. Calyx five-leaved ; corolla tubular, 

 with a five-clefted border, and five-hood- 

 ed scales between the segments; sta- 

 mina inserted in the throat under each 

 scale; stigma three-cleft, capsule supe- 

 rior, three-valved, three-celled from the 

 inflected valves ; seeds solitary, compress- 

 ed. One species, a shrub found in Aus- 

 tralasia. 



CUBJEA, in botany, a genus of the De- 

 candria Monogynia class and order. Na- 

 tural order of Lomentaceae. Legumino- 

 sae, Jussieu. Essential character : calyx 

 turbinate, five-parted, unequal, perma- 

 nent ; petals five, unequal; filaments vil- 

 lose, three shorter; germ pedicelled ; 

 legume villose, six or seven seeded. There 

 are two species. 

 CUBATURE, of a solid, in geometry. 



