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APPENDIX- 



ON DRAWING THE 



of the primary figure we are about to truncate, into 

 such a number of equal parts, as may enable us to 

 construct the required secondary planes by finding 

 the intersections within the same figure ; the other, 

 and, generally, the better method, is to produce the 

 primary edges, and to obtain the intersections either 

 within or without the figure, as may be most con- 

 venient. 



Fig. 381. 







As an example of the first of these methods, let us 

 suppose we have to represent a square prism modified 

 on its terminal edges by planes belonging to class c 

 of the tables of modifications, resulting from a de- 

 crement by one row of molecules, and whose symbol 

 would consequently be B. 



Let a square prism be drawn in pencil, of the 

 relative dimensions of the prism to be represented. 

 Divide the terminal edges into any number of equal 

 parts, let us suppose into 7 parts, and at a distance 

 from the angle, of two, or any other number of 

 those parts, draw the lines a 6, c d, and their parallels 

 on the upper and lower planes of the figure. Draw 

 bf 9 and c/, parallel to the diagonals of the planes 

 on which they are drawn, and e f, f g, and their 

 parallels, on the lateral planes. The line hf, is one 

 of the intersections of the modifying planes, and is 

 consequently a new edge of the secondary figure. 



