428 APPENDIX ON DRAWING THE 



to u v; and as it is evident that the line a d passes 

 through the middle of the plane g h 1 i /*, that plane 

 will represent the required plane c. By drawing 

 lines parallel to g 7z', and i A:, at corresponding dis- 

 tances from the diagonals q r, s t, and from the points 

 <7, r, s, and 5 the figure with the planes h and c upon 

 it may be completed, and may be traced separately 

 in pencil as in No. 3, preparatory to the addition of 

 the planes e. 



To produce these planes, having first drawn k x^ 

 we require the position of the intersection k /, of the 

 planes c and e. This intersection is shewn in No. 1 

 by the line a c ; the points a and c being common to 

 the plane a c e e', which corresponds to e, and a c c', 

 which, as we have already seen, represents c. 



If, therefore, from the point /j, No. 3, we draw k I 

 parallel to a c, No. 1, and from the point I 1 we draw 

 I y parallel to k x, the plane k I y x will be one of 

 the required planes e. The other planes e may be 

 drawn in a similar manner, or by parallels, or by 

 finding the relation of the point / to some known 

 point of the crystal. 



The planes e are purposely left incomplete in the 

 front and back of No. 3, where the planes b are to 

 be placed. 



