20 CRYSTALLOGRAPHY. 
Again, fig. 20 represents a cube with three planes on each 
angle, which, if enlarged to the obliteration of the faces of the 
cube, become the trigonal trisoctahedron, fig. 21. So again, fig. 

22 represents a cube with six faces on each angle, which, if en- 
Jarged to the same extent as in the last, would become the hex- 
octahedron, fig. 23. 
Again, fig. 25 is a form between the octahedron (fig. 24) and 

dodecahedron (fig. 26); and figs. 27 and 28 are forms between 
the dodecahedron, fig. 26, and trapezohedron, fig. 29. 
