490 
ON DRAWING CRYSTALS 
line A"D") till B" L (Fig. 7.) becomes equal to A" A^^' 
(Fig. 6.), the edges of the hexahedron B B" will 
assume the situation of B^ K, B" G, and the line B" H, 
which is determined by drawing GH at right angles upon 
the continuation of B B^^, will be the required length of the 
perpendicular lines in the projection. 
By the length B" H, taken upon A"^ A", C, B B", 
jyiu fj.Qjjj tj^g angles A^, C, B^, of the projection 
of the square, is determined the place of the four other 
solid angles of the hexahedron, which is thus completed, 
similar to Fig. 1. 
In order to express these processes analytically, let 
A" D'^, the distance of the two extreme edges, be ~ a ; 
A^^ C, the distance of one of these from the adjacent inte- 
rior one, = ^; A^^ A^^, the height of the projection of the 
terminal square, = ^ ; and, moreover, the length of an 
edge of the hexahedron = h. 
From the rectangular triangle D C D^^ follows, 
mn ^ 
And from the similarity of the triangles BVL B" and 
B" H G, Fig. 7., 
B 
m 
If, as in M. Mohs' Works, A" C is =: ^, A^^ A" = 
or m = 8, and n = 4, we have 
37 
64 64 
Thus it appears that this method of projection may, with 
