504 



INDEX. 



D 



Decrements, defined, 18. in breadth, 18. in height, 18. 

 simple, 20, 67. mixed, 21, 67. produce planes some 

 of whose edges are parallel to some edge or diagonal of 

 the primary form, 67. intermediary, 22, 69, produce 

 planes, none of whose edges are parallel to any edge or 

 diagonal of the primary form, 69. produce secondary 

 planes, 24. examples of the manner in which they 

 produce secondary forms, 71. the causes by which 

 they are occasioned not yet understood, 73. may 

 possibly take place on secondary crystals, 74. influ- 

 enced by the pyro-electricity of bodies, 76. their des- 

 criptive character in relation to secondary forms, 234. 

 theif relations to the different classes of modifications, 

 253 to 382, Calculation of the laws of, see CALCU- 

 LATION. their effect explained in modifying crystals, 

 288 the laws of, determined from the parallellism of 

 the edges of crystals, 393. 



Diagonal, of a plane, defined, 12. oblique, 12. horizonal, 

 12. 



Diagonal plane of a solid, defined, 12. 



Dodecahedron, rhombic, defined, 7. its relation to the 

 cube as shewn by cleavage, 44. its relation to cubic 

 molecules, 47. its cleavages explained, 63. solids 

 produced by cleavage do not represent its molecules, 

 64. its modifications, 120. 



Drawing the figures of crystals, methods of, 402, 438 the 

 principle explained, 403 to 406. 



E 



Edge of a crystal defined, 1. 



Edges of a crystal, terminal, defined, 3 lateral, defined, 3 

 similar, defined, 3 if replaced by 1 plane, are trun- 

 cated, 24 if by 2 planes, bevelled, 24. 



Elementary particles, defined, 5. 



Elements of a primary form, 286. 



Epigene crystals, 93. 



F 



Fluate of Lime, see Lime, fluate. 



Form, primary, defined, 6, 79 may sometimes be deve- 

 loped by cleavage, 79 frequently requires the aid of 

 secondary forms for its determination, 81 how deter- 

 mined from cleavage or from secondary forms, 81. 



