232 



SPECIMENS ILLUSTRATING CRYSTALLOGRAPHY. 



The following series of models are in glass boxes, showing in their 

 interior, by means of wires of different colours, the chief forms 

 derived from the typical crystal which the box represents. These 

 forms are arranged in this list, as if commencing from the centre and 

 proceeding to the outside of each glass box. For representations 

 of these forms, see Per. Mat. Med., vol. i. p. 142-147. The 

 numbers in parentheses refer to the figures in that work : 



656. I. REGULAR SYSTEM. (Tetrdhedric, Monometric, Octahedral, 

 Cubic, Equal-axed system.") 



a. Cube (Fig. 17) showing the following forms : 



Red, cube. (fig. 20.) 



Yellow, octahedron, (fig. 18.) 



Dark Blue,* rhombic dodecahedron, (fig. 19.) 



Black line in glass itself, tetrahedron, (fig. 21.) 



b. Cube. 



Yellow, *octahedron. 



White line in glass, tetrahedron. 



c. Cube. 



Red, cube. 



Pale yellow, octahedron. 



Dark blue, rhombic dodecahedron. 



Orange, *trapezohedron. 



Green, *four-faced cube. 



d. Cube. 



White, cube octahedron. 



Green, macles. 



Red, cube. 



Yellow, *octahedron. 



White and blue lines on the glass, tetrahedron. 



Note. In the above models some forms are more easily distinguished 

 in model a than in b, c, or d, and vice versa ; those which are most 

 readily seen are marked with an asterisk in the list. 



It will be observed that the same colour indicates the same form 

 in each model ; thus yellow is the colour used for the octahedron, red 

 for the cube, orange for the trapezohedron, dark blue for the rhombic 

 dodecahedron, and white on one side and dark blue or black on the 

 opposite side for the tetrahedron. All the above models will also be 

 observed to have three equal axes, each of which is at right angles to the 

 others; these are indicated by the red wires in the centre of each 

 cube. 



