498 ON DRAWING CRYSTALS 
and consequently, by eliminating c from the two first we 
obtain 
from the two last, 
(2 — n) 
2* 
, , . (1—2 n) m (2 — n) 
and therefore \^ .-^j ~ ; 
which being resolved, gives 
m = — — ^ ^ 7 — rr — — and 
- 7/z (m — 2) 
For w = 3, m becomes = r= i or 5, the former of 
which is excluded by comparing the result with the figure, 
and the only value left for w is = 5. The line O N, there- 
fore, is — 1 O K — J 6. The ratio of the lines a and h 
themselves, being expressed by = is 
The apparent length C D of the edge C E, parallel to 
the axis of the six-sided prism, is obtained from the simi- 
larity of the triangles C E D and A C B, and found to be 
eal 
= we suppose B C and c the r 
length of one of the sides of the regular hexagon. Since, 
by the preceding formula, as well as b, may be expressed 
by a and it will not be difficult also to express the length 
C D by means of the same quantities, although the expres- 
sion thus obtained will not be so simple as that stated 
above. 
