FIGURES OF CRYSTALS. 



The increased elevation of the point at i'", fig. 373, 

 may also be determined by drawing the arc c d, 



fig. 374, with a radius c b equal to of b, and 



making the angle c b d equal to 90 A t . The per- 

 pendicular c e will be the increased elevation of the 

 point at '", fig. 373, and the line e b will be the 

 horizontal projection of the lesser terminal edge of 

 the prism. 



Having thus obtained the horizontal projections 

 of the terminal edges of the prism, we may find the 

 vertical projections of the lateral edges in the fol- 

 lowing manner. 



Let the horizontal projection of the greater diago- 

 nal of the terminal plane be supposed parallel to the 

 line i m, fig, 373, and the diagonal g e of the plan 

 g b e h 9 must be parallel to the same line. 



Fig. 375. 



The edges of this plan are known from the figure 



374. The length of the line g e may be determined 

 by simply cutting a card so that the angle g b e, fig. 



375, shall be equal to / 3 , and making b g, equal to 

 b g-, fig. 374, and b e, equal to b e of the same figure. 

 The point b of the card being laid on the point b of 

 fig. 373, the edge ge may be made parallel to i ra, by 

 means of a parallel ruler, and the lines g b, be, being 

 traced by a pencil, their parallels h , h g, may be 

 drawn to complete the plan. 



