494 
ON DRAWING CRYSTALS 
Problem V. To draw a Scalene Four-sided Pyramid^ 
for instance^ that of Prismatic Topaz. 
According to Mohs, the ratio of the axis, and the two 
diagonals of the base in this species, or a : 6 : c is 
= 1 : V4.440 : V1.S38, or = : 1 ^Ijf . 
Draw the pyramidal axes AX, B and C of the 
hexahedron (Fig.13.). TakeA^M^X^M^AM - J , 
C"M C"iM = C M .jl^, and join the six points 
^ 4.44!0 
B C" B^ X^ by straight lines, the result will be the 
projection of the required pyramid. The numerical values 
must be expressed in decimals, and taken from a scale. 
Problem VI. To draw a Right Rhombic Prism. 
It is evident, that the projection of any oblique-angular 
four-sided prism will be as easily obtained as the projection 
of a scalene four-sided pyramid, if we suppose it, in a si- 
milar manner, to be inscribed into the hexahedron. The 
prism being a pyramid, one of the axes of which only is 
infinite, the present case forms a corollary of the preceding- 
one. 
Let, for instance, the prism (Fig. 14.) which is to be 
represented, be that, whose transverse section is similar to 
the base of P in prismatic Topaz^ or P-j- oo. The line 
M C = M r= C" = C"S will be equal to 
V 4.440 
