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 solid, 

 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 table, 

 which, strictly speaking, is nothing but a 

 very compressed prism ; it is defined as 

 composed of two parallel lateral planes 

 and of an indeterminate numberof terminal 

 planes, connected with the lateral planes 

 and with each other, and small, compar- 

 ed with the lateral ones ; the principal 

 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 composed of 

 a convex and a concave plane. These 

 simple figures are modified by combina- 

 tion, by truncation, by bevelment, 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, as in the double four-sided 

 pyramid", 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 

 appear 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 trun- 

 cated : fig. 30, the six-sided prism, with 

 truncated terminal edges .- fig. 31, the 

 same prism, with both the lateral and 

 terminal edges truncated. 



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 1 

 smaller converging planes, which termi- 

 nate 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, 

 acuminated by four planes set on the late- 

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

 acuminated by six planes set on the late- 

 ral planes. This kind of modification is 

 often described as consisting of the prima- 

 ry form, with pyramidal terminations. 



The forms of crystals from the preced- 

 ing modifications are frequently still more 

 altered, and rendered complicated, by be- 

 ing super-added and combined; and by 

 the extent of the modifications, one form 

 frequently passes into another. The fi- 

 gures 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 

 subject, particularly as related to mine- 

 ralogy* reference may be had to Wea- 

 ver's translation of the "External Cha- 

 racters of Minerals," by Werner ; or the 

 treatise on the same subject by Professor 

 Jameson. See CHTSTALLIZATIOX. 



CRYTANDRA, in botany, a genus of 

 the PentandriaMonogynia class and order. 

 Calyx five -leaved ; corolla tubular, with a 

 five-clefted border, and five-hooded scales 

 between the segments; stamina inserted 

 in the throat under each scale ; stigma 

 three-cleft, capsule superior, three-valv- 

 ed, three-celled from the inflected valves; 

 seeds solitary, compressed. One species, 

 a shrub found in Australasia. 



CUBJEA, in botany, a genus of the DC- 

 candria Monogynia class and order. Na- 

 tural Order of Lomentacex. Legumino- 

 sx, 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. 



