MODIFICATIONS. 273 



2. Intermediary. 



(B'p h q Br : B P h q B'r) represents another 



part of the series of class d. 

 The corresponding decrements on the obtuse solid 



angles are, 

 P 



O. 

 i 

 O. 



p o p . 



(D'p H q Dr : D'r H q Dp). 



Decrements on the lateral solid angles, are all com- 

 prised within class e. 



1 . Simple and mixed. 



i 

 E represents the middle plane of the class. 



E is the symbol, when the intersection of the 

 planess e and P, is parallel to the oblique 

 diagonal of P. 



When the lateral planes are intersected 

 by the planes e, parallel to a diagonal, 

 the symbol will.be either P E or E p . 



2. Intermediary. General symbol (Bp Gq Dr). 



In this symbol the comparative values of p, q^ 

 and r, will vary according to the positions 

 of the planes represented. 



Decrements on the acute terminal edges. 



\ 

 B represents the middle plane of class g. 



P 



B is the general symbol of that class. 



2 M 



