418 



APPENDIX- 



N DRAWING THE 



To draw the Tetrahedron. 

 Fig. 378. 



~f" FT^ 



/ * *f I A 



Draw a b of the length which is intended to be 

 given to the dotted edge a" b" of the figure, and draw 

 p q parallel to a b. 



On a b construct the equilateral triangle a b c, and 

 through its centre h draw d c, which will be perpen- 

 dicular to a b. From the points , &, c, and /?, draw 

 the oblique lines to p q^ and from the points where 

 they cut that line at a', &', h! 9 draw the perpendiculars 

 shewn in the figure. Having determined the quan- 

 tity of elevation to be given to the back of the tetra- 

 hedron, make k d, on the line a b, equal to that 

 quantity, and join k c ; and through the centre h 

 draw fg parallel to a b. On the perpendiculars from 

 a' and &', take a' a", and b 1 b", each equal to k d, and 

 by drawing the lines c' a", c' b", and a" b 11 , the base 

 of the figure will be delineated. To complete the 

 figure we require the line o m, which is the height 

 of the crystal. To obtain this we must have recourse 

 to the following geometrical construction. 



