268 RELATION OF DECREMENTS TO 



2d. Those which result from intermediary decre- 

 ments, which may be represented by this 

 general symbol, 



(Cp Gq Br). 



in which p, q, and r, will vary relatively to 

 each other as the decrements proceed along 

 the plane P, M ? or T. 



Decrements on the terminal edges. 



p 



General symbols, C represents class b. 

 p 

 B . . class c. 



Ifp == 1, in either of these symbols, a middle 

 plane will be represented belonging 

 to each class respectively. And the 

 planes of each class would respec- 

 tively incline more on the terminal, 

 or on the lateral plane, than its cor- 

 responding middle plane does, as 

 p is ]> 1, or <^ 1. 



Decrements on the lateral edges, producing the planes 

 of class d. 



These are of three kinds, and require three general 

 symbols. 



1. G /p P G, when the decrement proceeds along 



the plane M. 



2. P G' G p , when the decrement proceeds along 



the plane T. 



3. When p zz 1, in either of the two preceding 



symbols, the middle plane of the series 

 will be represented. 



