a i AE lt ce a Ri 
On the Drawing of Figures of Crystals. 45 
srow is the plane 2Pa (2: ow :1); for it cuts off 2 of ¢ and } of 
e, or 2 parts of € to 1 of €. 
The perimeters of the planes vntu (3Pc ) and mno (P) intersect 
in the points n and «; the intersections of 2Po with P has there- 
fore the direction «n, ind is parallel with the “edge a: 0’ in figure 10. 
The perimeters of the planes vntu (2Po ) and mro (2P2), inter- 
sect in the points « and 7; and a line from « to y marks the direc- 
tion of the edge between the planes 2Pm and 2P2. 
The perimeters of the planes srow ous ) and mro (2P2), coin- 
cide in the line ro. The intersection of 2Pa and 2P2 has there- 
fore the direction ro and is parallel with the edge 6 : a’ in fig. 10. 
Again, the plane gmol represents P w, (1: 1 : » ) for it cuts off 
equal parts of the edges e and é. The perimeters of the planes 
gmol and nmo (P) coincide in the line mo; their intersection is 
therefore parallel to this line, or to the edges a : 6 and 6: M, fig. 10. 
The perimeters gmo/ and npb (4P2) intersect in the points « and 
¢; aline from « to ¢ therefore marks the direction of the edge be- 
tween Po and 4P2 (0’). 
Again, the plane prkh is the projection of oP (a:1: 1), for 
it cuts off equal portions of é and é, and is parallel with the lateral 
edge. The perimeters prkh (@ P) and mbn (2P) intersect in the 
points « and ¢; a line between these points is parallel with mn. 
The intersection of these planes will therefore be parallel with mn, 
or the edge-a ; a’ (fig. 10.) 
The perimeters prkh (a P), and pnb (4P2) intersect in the points 
pand¢, A line drawn from p to ¢ determines therefore the inter- 
section of oP and 4P2 (6’). 
Fig. 12. Fig. 13. 
Fig. 12, contains these additional planes laid down according to the 
above deductions. The edge a : &’(3Po ) is parallel with the edge 
aio’; the edge é ; 6 has the direction «j ; the edge €’(2P@ ) : 6 
