48 On the Drawing of Figures of Crystals. 
not terminate in the vertices of the solid angles, and may therefore 
be thrown out of view in the projection of these solids. The two 
halves of each trigonal interaxis, terminate in the vertices of dissim- 
ilar angles, and are of unequal lengths. One is identical with the 
corresponding in the holohedral forms, and is called the holohedral 
portion of the interaxis ; the other is the hemihedral portion. ‘The 
length of the latter may be determined by adding to the half of the 
octahedral interaxis, that portion of the same indicated in the for- 
mula, 
2 mn—(m—n) 
mn-+-(m—N) 
If the different halves of the trigonal interaxes, be assumed at one 
time as the holohedral and again as the hemihedral portion, the re- 
O On 
verse forms = and ae may be projected. The following 
table contains the values of the above fraction for several of the in- 
clined hemihedral forms and also the corresponding values for the 
holohedral portion of the interaxis. 
Tfolohed. interax. Hemihed. interax. 
Tetrahedron (fig. 30.) Fu ¥ 2 
a 202 
Trigonal hemitrisoctahedron (fig. 34.) ogo 4 2 
: 30 
ry. g il *. tuk Bf (fig 40.) 7) 2 5 
ce 20 1 
Bi ad 1 
: 302 
Inclined hemihexoctahedron (fig. 41) —y~ 3 5 
AO2 
2 Sp toret 5 
505 
6c 5) z s 
23. The parallel hemihedrons, (for example, the Pentagonal 
Dodecahedron, or Hemi-tetrahexahedron) contain a solid angle, sit- 
uated in a line between the extremities of each pair of semiaxes, 
which is called an unsymmetrical solid angle. The vertices of 
these angles are at unequal distances from the two adjacent axes, 
