FIGURES OF CRYSTALS. 



409 



To draw a Right Rhombic Prism. 

 Fig-. 371. 



Let a b represent the greater diagonal of a right 

 rhombic prism, and let the rhomb a c b d represent 

 the base of the particular prism we are about to de- 

 lineate. 



The angle a d b of the prism is supposed to be 

 known, and that angle of the figure may be made 

 equal to it, by adjusting the arms of the common 

 goniometer to the required angle, and using them as 

 a rule to draw the lines a d, d b. 



Draw e h parallel to a b ; and also the oblique lines 

 a f> c g 9 dh, b /, these being, as before, drawn more 

 or less oblique, according as we wish to exhibit a 

 greater or less difference between the two lateral 

 planes of the prism shewn in the front of the figure. 



To elevate the back part of the prism in order to 

 exhibit the terminal plane, take i i' equal toff; and 

 draw h i', h f, and their parallels. 



Let the lateral edge h k be drawn in such proportion 

 to the terminal edge a d, as it has been found by cal- 

 culation on the particular crystal we are delineating ; 

 and draw the upper terminal edges parallel to the 

 lower ones. 



3 F 



