S. L. Penfield — Crystal Drawing. 



73 



ously determined, and 

 parallel to the direc- 

 tion from A to the 

 point cot. 45° 50' on 

 the vertical axis. In 

 the case of q 9 figure 

 55, being on the meri- 

 dian 58° 25' from 

 —B, a little explana- 

 tion is necessary : A 

 crystal face corre- 

 sponding to £, when 

 shifted so as to inter- 

 sect +B, will inter- 

 sect the negative ends 

 of the A and C axes ; 

 the former at the 

 point marked y, cot. 

 58° 25', which is pro- 

 jected down on the A 

 axis beneath. The 

 great circle through 

 — B and q makes an 

 angle of 56° 10' with 

 the equator, and the 

 point cot. 56° 10 r is 

 laid off in this case 

 on the negative end 

 of the C axis. The 

 linear projection of q 

 is then the line rum, 

 drawn through y and 

 parallel to the direc- 

 tion from —A to the 

 point cot. 56° 10' on 

 the vertical axis. 

 The lines nn and mm 

 intersect at some dis- 

 tance from the cen- 

 ter of the axes, but 

 if continued it is 

 found that a line from 

 ■\-B to their point of 

 intersection is parallel 

 to the direction Oi. 

 If it is desired to make 

 the linear projection 



56 



