508 INDEX. 



s 



Secondary form, see Form, secondary. 



Secondary planes produced by decrements, 24 said to re- 

 place angles or edges, 24. 



Similar edges, angles and planes, defined, 3. 



Species, mineral, defined, 6. 



Square, defined, 4. 



Structure of crystals, or the order in which their molecules 

 are arranged, illustrated by an experiment with com- 

 mon salt, 53 this regular order supposed to belong to 

 all regularly crystallised bodies, 54 of the cube, regular 

 tetrahedron and octahedron, and rhombic dodecahedron, 

 explained, in relation to the theory of cubic molecules, 

 46 & 47 ultimate relation ol tetrahedron and octahe- 

 dron, 65. 



Sulphate of Barytes, see Barytes, sulphate. 



Symbols, how applied to distinguish primary forms, 103 

 their character, 232 how applied to denote secondary 

 forms, 236 to 252 arranged in tables, 252 to 279 

 denoting intermediary decrements, compared with those 

 used by Haiiy, 281. 



Symmetry, general law of, 77 is sometimes suspended by 

 the pyro-electricity of bodies, 77 and by other causes, 

 78. 



T 



Tangent plane, defined, 24. 



Tetrahedron, regular, defined, 6 Its axis, 13 its relation 

 to the regular octahedron as shewn by cleavage, 40 to 

 42 its relation to the cube, 84 its relation to cubic 

 molecules, 46 its modifications, 112. 



Triangle, equilateral, defined, 3 isoceles, defined, 3 

 scalene, defined, 4. 



Truncated edge or angle, defined, 24. 



FINIS. 



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