MODIFICATIONS OF PRIMARY FORMS. 



33 



inclining equally upon the adjacent planes, as the edge in Fig. 44, 

 replaced by e and e f ; e' inclines upon M> at the same angle as eupon 

 M. An edge replaced in this manner is sometimes said to be bev- 

 illed. 4. An edge may be replaced by two planes which incline 

 unequally to their adjacent primary planes. Thus in Fig. 45, f 

 forms with M' a greater angle than e with M. 



Fig. 44. 



JFig. 45. 



M 



3. The variations among the modifications which take place at 

 the angles are still more numerous. 1. An angle may be replaced 

 by a single plane inclining equally to each one of the planes which 

 formed the angle. Thus, in Fig. 46, the secondary plane a inclines to 

 M' under the same angle which it does to M or P. 2. An angle 

 may be replaced by a plane inclining unequally to the adjacent pri- 

 mary planes. Thus, Fig. 47, b inclines to the three faces T, M 4 



Fig. 46. 



Fig. 47. 



1 



M 



P 



and P under different angles. 3. An angle may be replaced by two 

 planes, as in Fig. 48. The relative position of these secondary 

 planes to those of the primary is conveniently indicated by a refer- 

 ence to the direction of the edge formed by the intersection of the 

 two new planes. In the present instance, it may be said to incline 



