56 
GvYj on Crystals of Arsenious Acid. 
12 
The first section supplies the following forms : 
a. The equilateral triangle (fig. 10). 
b. The equilateral triangle resting on 
half the adjoining triangle as a 
base (fig. 11). 
This is a very common aspect of the 
half- crystal. 
c. The hexagon, (fig. 12.) 
d. The hexagon with the three small 
triangular facettes in shadow (fig. 
13). 
This also is a very common aspect of the 
half-crystal. 
e. The half- triangle (fig. 14.) 
/. The edge of the half- crystal tilted 
forwardjso as to give the appearance 
of a triangular prism (fig. 15) . 
This again is a very common aspect of 
the half-crystal. 
g. The made or twin-crystal, formed by 
the partial rotation of two half- 
crystals on each other (fig. 16). 
h. The same, with the triangular face of 
one half- crystal visible (fig. 17). 
second and third sections are of rare occurrence, and 
assume appearances requiring more minute description. 
15 
17 
The 
do not 
3. The rhombic dodecahedron. 
a. Three sides visible, so as to resemble the 
perspective of a cube (fig. 18). 
b. Four sides visible, and a solid angle pro- 
jected forward (fig. 19). 
c. Five sides visible (fig. 20). 
d. Five sides visible ; another aspect of the 
crystal (fig. 21). 
