Salts. 137 



forms of different crystallized bodies ; and thus 

 obtained the six primitive forms: 1. The Cube; 

 2. The tetraedon ; 3. The octoedron ; 4% The 

 hexangular prism; 5. The rhombic dodecae- 

 dron ; 6. The dodecaedro'n with triangular faces ; 

 and, by further* mechanical analysis, he re- 

 duced these to three integral elements. 1. The 

 parallelopepid, or simplest solid, having six sur- 

 faces, parallel two and two. 2. The triangular 

 or simplest prism, bounded by five surfaces. 3. 

 The tetraedron, or simplest pyramid, bounded 

 by four surfaces. The secondary forms are sup- 

 posed to arise from increments of particles taking 

 place on different edges and angles of the pri- 

 mitive forms. Some appearances, however, are 

 met with which Hauy^s theory does not satisfac- 

 torily explain. To obviate the difficulties which 

 here arise, Dr. Wollaston has proposed to con- 

 sider the primitive particles as spheres, which by 

 mutual attraction have assumed that arrangement 

 which brings them as near as possible to each 

 other. Mr. Daniel has perceived that a species 

 of alum being immersed in water and left quietly 

 to dissolve, the mass will present the forms of 

 octoedra and sections of octoedra, as it were 

 stamped or carved upon its surface. By this cu- 

 rious species of dissection it is to be hoped, that 

 such developements of the structure of crystals 

 may be detected as may give us more satisfac- 

 tory information respecting this most curious 

 natural process. 



