Mr. E. J. Chapman on the Notation of Crystals. 325 



It is, however, necessary, for the complete elucidation of the 

 proposed method,to examine separately the notation appertain- 

 ing to each crystallographic group. In the following scheme 

 numbers greater than unity are represented by m or n, and 

 those less than unity by ^. Placed before a letter, these refer 

 to the vertical axis ; and when placed after a letter, to one of 

 the other axes, as will be explained in the observations at- 

 tached to each system. 



Monometric System, 



Monaxial form : — 

 The cube, P. 



Diaxial forms : — 



The rhombic dodecahedron, A. 

 Tetratrishexahedrons, -A. 



' m 



Triaxial forms : — 

 The regular octahedron, O. 

 Leucitoidsoricositetrahedrons,-0. 



' m 



Trisoctahedrons, mO. 

 Hexakis-octahedrons, mOn. 



Fig. 1.^ 



Copper : Siberia. 

 Fig. 2. 



O 



Regular tetrahedron. 

 Other hemihedral forms, designated 

 after a similar manner, =-. 



Galena: Clausthal. 

 Observations. — In the less simple forms of this system, that 



* For several of these examples I am indebted to the beautifully executed 

 plates of Dufrenoy's Atlas, Traite de Mineralogie, 1846. I have, however, 

 added the axes to each figure, so as to render the positions of the different 

 planes more readily apparent. 



