MOLECULES. 



Fig. 72. 



i'jfo: 



Fig. 73. 





Fig\ 73 exhibits the dodecahedron contained in 

 fig. 72 ; this may be obtained by cleavages in direc- 

 tions corresponding with the lines a df, fig. 72, which 

 will remove the solid angles of the base on which fig. 

 72 and 73 rest. 



Fig. 74. 



Fig. 74 shews the position of the rhombic dodeca- 

 hedron in the cube. 



Having thus observed that the cube, the regular 

 tetrahedron and octahedron, and the rhombic dodeca- 

 hedron are common as primary or secondary forms to 

 different crystallized substances, we may reasonably 

 infer that they are produced in each instance by mole- 



