408 APPENDIX ON DRAWING THE 



To represent this elevation take some portion, as 



1 /r, of the line k a, and draw f i ; the portion i k 

 may be greater or less according as more or less of 

 the plane g I m h is required to be seen. 



Draw e w, g /, h m, parallel to fi ; and / m, n z, 

 parallel to g h, and the figure represents a cube. 



To draw a Square Prism. 



The square prism differs from the cube only in its 

 comparative height. 



Let us suppose we have to represent a square 

 prism, whose terminal edge is to its lateral edge as 



2 to 3; we may divide the terminal edge e f in 

 two parts, and make e o equal to three of those 

 parts, and then complete the figure as represented in 

 the diagram. And we may, by a similar proceeding, 

 make the lateral edge of the prism bear any given 

 proportion to the terminal edge. 



To draw a Right Rectangular Prism. 



To draw a right rectangular prism, make the lines 

 a c, c d, of the preceding figure, proportional to the 

 corresponding terminal edges of the particular prism 

 we wish to represent; and having proceeded to draw 

 and elevate the base of the figure as for the cube, 

 make e g proportional to the third dimension, or 

 height of the prism, and then complete the figure by 

 drawing the parallel lines as before. 



It has been already stated that when the angles of 

 the base of a prism, or octahedron, are right angles, 

 the figure of the crystal is drawn with one of the 

 edges of its base horizontal ; but where those angles 

 are not rignt angles, the diagonal of the base is hori- 

 zontal in the figure, and the terminal edges are 

 described by oblique lines. 



