LAWS OF DECREMENT. 



347 



THE RfGHT OBLIQUE-ANGLED PRISM. 



Its elements. 



The inclination of terminal on lateral planes nz 90* 

 Inclination of lateral planes to each other 

 varies in the different individuals belonging to 

 the class. Call the greater angle at which 

 they incline to each other, /, . 

 Terminal plane angles are consequently I l9 

 and (ISO /,), but they will be called A, 

 and A z . 



Lateral plane angles ~ 90. 

 The adjacent edges unequal. Their ratio, and 

 that of the diagonals of the terminal planes, 

 can be known from secondary planes only. 



Its units of comparison. 

 Fig. 351. 





When the edges of any plane of class a or &, of the 

 modifications of this form, which intersect the plane 

 P, are parallel to a diagonal of that plane, the modi- 

 fying plane results from a simple or mixed decre- 

 ment. 



The unit of comparison for determining the laws 

 of simple or mixed decrements belonging to class a, 



