S. L. Penfield — Crystal Drawing. 



55 



sponding points above, and the length of the vertical axis 1-316 

 is laid off above and below by means of the scale of decimal 

 parts, at points marked 1 and —1 in the figure. The lines of 

 the linear projection needed for the two sets of axes are as 

 follows : For the brachydome o, Oil, the lines xz and x'z\ 

 through b parallel to the a axis : For the macrodome d, 102 

 (2a : oo h : c), the lines xy and x'y', through 2a parallel to the 

 b axis : The prism m (110) is parallel to the vertical axis, 



25 



hence in order that such a plane shall satisfy the conditions of 

 the linear projection and pass through unity on the vertical 

 axis, it must be considered as shifted (without change of direc- 

 tion) until it passes through the center : Its linear projection 

 therefore is represented by the lines yz and y'z\ parallel to the 

 directions a to b on the two sets of axes. Since a linear pro- 

 jection is made on the plane of the a and b axes, the intersec- 

 tion of any face with the base (001) has the same direction as 



