CRY 
ral planes may of course be Tarious ; the 
usual form observed in crystals are the four- 
sided rectangular prism, fig. IT ; and tlie 
six-sided equiangular prism, fig. 19. 6th, 
The pyramid, or solid, the base of which is 
a plane of an indeterminate number of 
sides, and tlie sides triangles, the vertices of 
which meet in one point, forming the sum- 
mit : the more common varieties of this fi- 
gure, 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 
number of terminal planes, connected 
with the lateral planes and with each other, 
and small, compared with the lateral ones ; 
the principal varieties are, the oblique-an- 
gular, 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 con- 
vex planes, and another composed of a con- 
vex and a concave plane. These simple fi- 
gures are modified by combination, by 
truncation, by bevelment, and by acumina- 
tion. 
The modification by combination are 
confined to the pyramids, and these are fre- 
quent, two pyramids being joined by the 
base ; the lateral planes of the one beint^ 
set either directly on the lateral planes of 
the other, as in the double four-sided pyra- 
mid, 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 truncated : fig. 30, the six-sided 
prism, with truncated terminal edges ; 
fig. 31, the same prism, with both the late- 
ral and terminal edges truncated. 
A crystal is said to be bevelled, when its 
edges, angles, or terminal planes are so al- 
tered, that instead of an angle edge or ter- 
ming plane, there appear two smaller con- 
verging planes, which terminate in an edge: 
fig. 32, shews the cube with beveUed 
edges: fig. 33, the three-sided pyramid. 
CUB 
with bevelled edges : fig. 34, the oblique 
four-sided prism, bevelled on both extremi- 
ties. 
Lastly, tlie 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. 33, shews the cube, 
with angles acuminated by three planes set 
on the lateral planes : fig. 36, the rectangu- 
lar four-sided prism, acuminated by four 
planes set on the lateral planes : fig. 37, 
the six-sided prism, acuminated by six 
planes set on the lateral planes. This kind 
of modification is often described as con- 
sisting of the primary form, with pyramidal 
terminations. 
The forms of crystals from the preceding 
modifications are frequently still more al- 
tered, and rendered complicated, by being 
super-added and combined; and by the ex- 
tent of the modifications, one form fre- 
quently passes into another. The figures 
of crystis are likewise rendered compli- 
cated 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 as related to mineralogy, 
reference may be had to Weaver’s transla- 
tion of the “ External Characters of Mine- 
rals,” 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 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- valved, three- 
celled from the inflected valves ; seeds so- 
litary, compressed. One species, a shrub 
found in Australasia. 
CUBAIA, in botany, a genus of the De- 
candria Monogynia class and order. Na- 
tural order of Lomentace®. Leguminos®, 
Jussieu. Essential character : calyx turbi- 
nate, five-parted, unequal, permanent; pe- 
tals five, unequal; filaments villose, three 
shorter ; germ pedicelled ; legume villose, 
six or seven-seeded. There are two spe- 
cies. 
CUBATURE of a solid, in geometry, 
the measuring the space contained in it ; or 
finding the solid content of it. 
CUBE, in geometry, a solid body, consist- 
ing of six equal square sides. The solidity 
