.29.30. 31. OF FOKMS IN GENERAL. 29 

 . 29. EDGES. 



The limits of the faces, or their intersections 

 with each other, are termed Edges. 



The Edges of forms are always supposed to be straight 

 lines, although in nature they are not always straight. 



The Edges are denominated not only according to the 

 forms to which they belong, but also according to their par- 

 ticular situation in respect to these forms. If a form of 

 crystallisation contain edges of only one kind, these bear 

 simply the name of the form ; as, for instance, Edges of the 

 Hexahedron. If it contain several kinds of edges, they are 

 distinguished from each other by their name, for in- 

 stance, Terminal and Lateral Edges of the Rhombohe- 

 dron, &c. 



. 30. SOLID ANGLES. 



The limits or terminal points of the edges are 

 Solid Angles. 



The solid angles are named according to the forms in 

 which they are found, and receive a nearer determination, 

 by some epithet expressing their particular situation and 

 quality. Thus we say, Solid Angles of the Hexahedron ; 

 also rhombohedral, pyramidal, prismatic Solid Angles, &c. 



. 31. HOMOLOGOUS FACES. 



Faces, equal and similar to each other, and simi- 

 larly situated, are termed homologous ; such as are 

 not equal and similar, or assume a different situa- 

 tion in the forms, are not liomologous. 



In nature, the homologous faces are not always equal 

 and similar to each other, yet they are always similarly 

 situated. Sometimes a single face of a crystalline form k 



