MODIFICATIONS. 267 



* 



The right Rectangular Prism. 

 Fig. 314. 



M 



Decrements 'on the angles. 



The planes belonging to class a, comprehend the 

 following varieties. 



1st. Those which result from simple and mixed 



decrements on the 



P 

 terminal angles, of which the general symbols is A. 



angles of plane M, P A. 



angles of plane T, A 1 '. 



Ifp = 1, in either of these symbols, the same 

 individual plane belonging to the 

 class is represented by each ; the 

 three edges of which are, respective- 

 ly, parallel to the diagonals of the 

 planes P M and T. This may be 

 termed the middle plane of the series. 

 p ^> 1, the planes represented will incline on 

 the plane P, or M, or T, more than 

 the middle plane does. 



p <^ 1, the plane represented will incline less 

 on the respective primary planes than 

 the middle plane does. 



