INDEX. 



A 



Angle, plane, defined, 2. its measure, or value, how deter- 

 mined, 2. right, 2. acute, 2. obtuse, 2. 



Angle, solid, defined, 2. said to be replaced by secondary 

 planes, 24. if replaced by 1 plane, is truncated, 24. 



Angles, at which the planes of crystals incline to each other, 

 how determined, 25. how measured by the common 

 goniometer, 26. and by the reflective goniometer, 30. 

 similar, defined, 3. 



Arrangement of minerals, 439. must vary with the object 

 of the collector, 440 an alphabetical arrangement pro- 

 posed, 441. and given, 451 to 497. a chemical basis 

 considered, 442. an optical, 446. 



Attraction, molecular, 48. may differ indifferent directions 

 of the molecules, 48. 



Axis of a crystal, defined, 12. oblique, 12. prismatic, 12. 

 of a cube, 13. of a tetrahedron, 13. of octahedrons, 

 13. of a rhombic dodecahedron, 13. of prisms, 14, 

 - 15, 16. of a rhomboid, 16. 



B 



Barytes, sulphate, molecule similar to primary form, 38. 

 Bergman's theory of crystals, 33. 

 Bevelled edge, defined, 24. 



Bournon, Comte, first described crystals by their modifica- 

 tions, 34. 



C 



Calculation of the laws of decrement, general method, 285 

 to 303. applied to the cube, 304. to the regular te- 

 trahedron, 308. to the regular octahedron, 313. to 

 the rhombic dodecahedron, 320. to the octahedron 

 with a square base, 325. to the octahedron with a 

 rectangular base, 330. to the octahedron with a rhom- 

 bic base, 335. to the right square prism, 339. to the 



