ON THE USE OF SYMBOLS. 



be unaccompanied by any other symbol, it would be 

 implied that all the solid angles were similarly mo- 

 dified. The symbol representing class C might be 



The planes of modification a of the cube might be 



denoted thus. A, but for the sake of uniformity with 



the preceding symbol, they will be represented by 



i 

 the symbol * A * . 



The planes belonging to class i of the cube, do not 

 differ from those belonging to class d, except in being 

 three single similar planes, instead of three pairs of 

 similar planes, as there are in class d. To distinguish 

 class d therefore, by its symbol, it will be requisite 

 that the symbol should represent one of the pairs of 

 planes, and not merely a single plane, as might have 

 been sufficient if class i had not existed. 



Suppose an individual modification belonging to 

 class d is to be denoted, and if the decrement pro- 

 ducing it be by three molecules on the edge B, one 

 on the edge B',* and two in height on the angle A, the 

 symbol would be 



(B3 B'"2 B'l : Bl B'"2 B'3), 

 which would imply a pair of planes resting on the 

 plane P. And the two symbols being both included 

 within a parenthesis, and separated from each other 

 by two dots, implies that both the planes represented 

 result from the same law of decrement, but acting in 

 two different directions. 



If two similar planes belonging to class f of the 

 cube, resulting from a decrement by three rows in 

 breadth, occur on all the edges of a cubic crystal, the 



symbol B will be used to denote their existence on 

 one of the edges ; and their existence on the other 



* B*, B", &c. is read B dash t B two dash, &c. 



