32 



CRYSTALLOGRAPHY. 



solid angles, as in the isometric octahedron. There may be, od 

 the same crystal, faces of several octahedrons of these two series, 

 differing in having their planes inclined at different angles to 



19. 



'W\ 



^=P \kJ 



the basal plane. In figs. 5 and 7 there is one of these pyra- 

 mids terminating the prism, and in figs. 6 and 8 the planes 

 of two. In figs. 1 to 3 there are planes of the same octahe- 

 dron, but combined with the basal plane ; and in fig. 4 there 

 are planes of two, with 0. In fig. 9 there are planes of the 

 same octahedron, with planes of a square prism (i-i), and of an 

 eight-sided prism (^-2). In fig. 18 there is the prism i-i com- 

 bined with two octahedrons, and the basal plane ; and in 

 19 the planes of one octahedron with the prism I. 



Fig. 20 represents an eight-sided double pyramid, made of 



21. 



equal planes, equally inclined to the base ; and fig. 21, the sam* 

 planes on the square prism i-i. The small planes, in pairs, on 

 fig. 8, are of this kind. In fig. 22 the small planes 3-3 of 

 fig. 8 occur alone, without planes of the four-sided pyramids, 

 and therefore make the eight-sided pyramid, 3-3. 



This solid of sixteen planes has the largest number of similar 

 planes possible in the dimetric system, while the largest number 

 in the isometric system (occurring in the hexcctahedron) is 

 forty-eight. 



