248 ON THE USE OF SYMBOLS. 



by symbols analogous in character to those used for 

 the octahedron. 



The modifications on the obtuse solid angles may 

 be represented by symbols resembling in character 

 those used for the tetrahedron. 



The Rhomboid. 



The modification on the superior edges may be 

 represented by the general symbol P B P , and those on 

 the inferior edges by the general symbol P D P . 



The modifications , b, c, e?, may be represented by 

 symbols of the same character as those adopted for 

 the tetrahedron. 



The remaining modifications, on the lateral solid 

 angles, may very obviously be conceived to result 

 from decrements upon either the angles at , or 

 the angle at O. For if we refer to any of the modi- 

 cations from e to /:, we may perceive that the planes 

 which replace the angles at E, are similar to those 

 which replace the angle at O, but are in an inverted 

 position. It is therefore indifferent, as far as the 

 representative character of the symbol is concerned, 

 whether we refer the planes belonging to any of those 

 modifications, to the angle at E or at O. Jn either 

 case, the symbols will be similar in character to those 

 which relate to the solid angles of some other paral- 

 lelepipeds. 



In the following tables, both these classes of sym- 

 bols will be again alluded to, and their differences 

 pointed out in reference to several of the classes of 

 modifications. 



In the examples which we have given of the appli- 

 cation of symbols to represent the secondary forms of 



