72 



W. G. WOOLNOUGH. 



Fig. 3. Hexagonal. 



Figs. 1, 2, 3, 4 — Nets to show construction of the models for 

 cubic, tetragonal, hexagonal, and rhombic systems. The 

 edges indicated by dotted lines are to be joined. 



A crystal face of the most general form is represented 

 by a triangle of cardboard of suitable size and shape. This 

 is placed in the solid angle between the three mirrors when 

 the multiple reflections will reproduce all the faces of the 



