506 tNDEX. 



of the regular tetrahedron, 112 of the regular 'octahe- 

 dron, 116 of the rhombic dodecahedron, 120 -of the 

 octahedron with a square base, 126 of the octahedron 

 with a rectangular base, 138 of the octahedron \v ith a 

 rhombic base, 146 of the right square prism, 162 of 

 the right rectangular prism, 166 of the right rhombic 

 prism, 170 of the right oblique-angled prism, 176 

 of the oblique rhombic prism, 180 of the doubly 

 oblique prism, 190 of the hexagonal prism, 196 of 

 the rhomboid, 200 on the application of the tables of, 

 223. 



Molecules, are homogeneous, 5 distinguished from elemen- 

 tary particles, 6 arrange themselves around a single 

 central molecule in the first formation of a crystal, 17 

 are afterwards added to the surfaces of the small crystal, 

 in plates, 18 are separable at their surfaces by mecha- 

 nical division, 36 their forms, in relation to the differ- 

 ent classes of primary forms, 37 of parallelepipeds, 

 are similar parallelepipeds, 38 of the hexagonal prism, 

 are triangular prisms, 38 of the regular tetrahedron, 

 regular octahedron, and rhombic dodecahedron, are 

 cubes, 51 of the irregular octahedrons, are particular 

 prisms, 51 Haiiy's theory of, relatively to the tetra- 

 ' hedron and all octahedrons, 42 and to the rhombic 

 dodecahedron, 43 objection to Haiiy's theory of, 43 

 new theory of, proposed, 45 of the cube, regular 

 tetrahedron, regular octahedron, and rhombic dodeca- 

 hedron, 46 new theory of, reconcileable with known 

 cleavages, 47 explained in reference to cleavages, 48 

 are so minute as to occasion no sensible diminution in 

 the brilliancy of planes constituted of their edges or 

 solid angles, 47. 



N 



Natural joint of a crystal is the direction of its cleavage, 56. 



-Nucleus defined, 74 how obtained by cleavage, 74. 



O 



Octahedron, regular, defined, 7 its axis, 13 its relation 

 to the cube as shewn by cleavage, 40 its relation to the 

 tetrahedron *ts shewn by cleavage, 40 to 42 its relation 

 to cubic molecules. 46 its cleavages explained, 60 

 the solids produced by cleavage do not represent its 

 molecules, 64 how it might be ultimately produced 

 from the tetrahedron, by the removal of cubic mole- 

 cules, 65 its modifications, 116. 



