34 



TERMINOLOGY. 



upon the superior edges of the Rhomboid. In other cases, it may be 

 parallel with the perpendicular axis of $iis solid, or it may incline 

 upon the primary planes. 



Fig. 48. 



Fig. 49. 



4. An angle may be replaced by three or more planes, according 

 as it was made up of three or more plane angles, as in Figs. 49 and 

 50. The secondary planes may repose upon the primary planes as 

 a upon P, Fig. 49, or 



Fig. 50. 



Fig. 51. 



5. the secondary planes may repose upon the edges of the*pri- 

 mary form, as in Fig 51.* 



* Additional kinds of modification might have been described ; but 

 as those mentioned above are the most frequent among crystals, and are 

 sufficient to render the subject perfectly intelligible, it was not thought 

 necessary to detain the student with the enumeration of others. 



