ON THE USE OF SYMBOLS. 247 



The regular Octahedron. 

 Fig. 305. 



The simple and mixed decrements on the angles, 

 which would produce the planes belonging to class b, 



may be represented by the symbol P A P ; which im- 

 plies that similar planes occur on the three adjacent 

 angles, and consequently on the fourth: 



The intermediary decrements are of two kinds, 



1. Those which produce the planes compre- 



hended under class c. 



The general symbol to represent these would 

 be (Bp B' q b' q br). 



2. Those which produce the planes compre- 



hended under class d. 

 The general symbol to represent these would 



be\B P B' q b'r b s : B P B'r b' q b s ). 

 These symbols denote the abstraction of /?. <y, r, or 

 s, molecules from some of the edges B, B', b', and b, 

 in the production of the planes belonging to classes 

 c 9 or d. 



The Rhombic Dodecahedron. 



The modifications on the edges of this primary 

 form may be denoted by the general symbol P B P . 

 Those on the acute solid angles may be represented 



