S. L. Penfield — Crystal Drawing. 



m 



55° 20', measured from B, and the distance from C is easily 

 determined as 49° 40' by means of a stereographic scale.* If 



55 



^*- -"- -cot. tsrifo' 

 we imagine a pole corresponding to p located on a spherical 



* For a description of the stereographic scales and protractors mentioned 

 in this and the succeeding paragraphs, the reader is referred to the earlier 

 publications of the writer : " The Stereographic Projection and its Possibil- 

 ities from a Graphical Standpoint," this Journal (4), xi, pp. 1-24 and 115- 

 144, 1900 ; and "On the Solution of Problems in Crystallography by Means 

 of Graphical Methods, based upon Spherical and Plane Trigonometry," 

 Ibid., xiv, pp. 249-284, 1902. 



