144 



ATTRACTION. 



by analogy. The angles which the sides make with each other, are 

 always the same in a nucleus, however obtained ; and such crystals 

 are always divisible in directions parallel to all their surfaces, where- 

 as there are some surfaces of secondary forms, parallel to which, by 

 cleavage, new facets cannot be obtained." 



" Haiiy enumerates six primitive crystalline forms, the parallele- 

 piped, (including the cube, rhomboid, and four sided prism,) the reg- 

 ular tetrahedron, regular octohedron, hexahedral prism, rhombic 

 dodecahedron, and dodecahedron with triangular faces." 



FIG. 3. Quadran- 

 gular or four- 

 sided prism. 



FIG. 4. Cube. FIG. 5. Rhomboid. 



FIG. 6. Tetrahedron. 



FIG. 7. Octohedron 



FIG. 8. Hexangular or 

 six sided prism. 



FIG. 9. Rhombic dode- 

 cahedron. 



