FIGURES OF CRYSTALS, 



407 



Having- thus given a brief outline of the theory of 

 geometrical projection, we shall proceed to shew 

 how the forms of crystals may be accurately deli- 

 neated, without entering into any further general 

 explanation of the means which will be employed for 

 this purpose. 



To draw a Cube. 

 , Fig. 370. 



On the line a 6, describe the square abed. Let 

 the line e k be parallel to a b. 



From the points a b c d, draw the lines c e, a r, df> 

 b #, and let these lines be more or less oblique, as 

 the side h f m i is to be rendered more or less 

 visible. 



Draw the perpendiculars e o, r <?, fp 9 k v. Take 

 e g equal ef, and draw g h parallel to ef, and e g hf 

 is consequently a square. 



For the purpose of shewing the plane g I m h of 

 the cube, the back of the figure is supposed to be a 

 little elevated. 



