208 
SPHERICAL ELEMENTS OF CRYSTALS. 
Hexagonal Prisms. 
Oblon<r sphe* elementary spheroid be, on the contrary, oblong, in- 
roids would stead of oblate, it is evident, that by mutual attraction, their 
give hexagonal •' 
priiiiiis. centres will approach nearest to each other when their axes ar« 
parallel, and their shortest diameters in the same plane (fig. 13-) 
The manifest consequence of this structure would be, that a 
solid so formed would be liable to split into plates at right 
angles to the axes, and the plates would divide into prisms of 
three or six sides, with all their angles equal, as occurs in phos- 
phate of lime, beryl, &c. 
It may further be observed, that the proportion of the 
height to the base of such a prism must depend on the ratio 
between the axes of the elementary spheroid. 
The Cube. 
The cube can- Although I could not expect that the sole supposition of 
not be formed spherical or spheroidical particles would explain the origin of 
by spheres ui ‘ r i i o 
contact; all the forms observable among the more complicated crystals, 
still the hypothesis would have appeared defective if it did not 
include some view of the mode in which so simple a form as 
the cube may originate. 
A cube may evidently be put together of spherical particles^ 
arranged four and four above each other ; but we have already 
seen, that this is not the form which simple spheres are 'natu- 
rally disposed to assume, and consequently this hypothesis 
alone is not adequate to its explanation, as Dr. Hooke had con- 
ceived. 
jior by cblate Another obvious supposition is, that the cube might be con- 
tpheroids. sidcred as a right-angled »-homboid, resulting from the union 
of eight spheroids having a certain degree of oblateness (2 to 
l) from which a r ctangular form might be derived. But the 
cube so formed would not have the properties of the crystal- 
lographical cube. It is obvious that, though all its diagonals 
would thus be equal, yet one axis parallel to that of the ele- 
mentary spheroid would probably have properties different 
from 
