28 TERMINOLOGY. . 27. 28. 



ter within a regularly limited space, yet want continuity, 

 and cannot therefore be called crystals in the signification 

 of that term, as defined above. 



. 27. OBJECT OF CRYSTALLOGRAPHY. 



The object of the science of Crystallography, is 

 to ascertain the regularly limited space, that is to 

 say, the Form of the Crystals, not the matter, 

 which occupies that space. 



Since the object of Crystallography is nothing but figur- 

 ed Space, and in this nothing is to be considered besides 

 geometrical quantities, and their relations to each other ; 

 it appears that Crystallography is a pure geometrical 

 science. 



. 28. FORMS AND FACES. 



The regularly limited space occupied by a crys- 

 tal, is termed a Form of Crystallisation, and the 

 limits or planes. Faces of Crystallisation. 



In Crystallography, the faces of crystallisation are con- 

 sidered as perfect Planes, although this is not always the 

 case in nature. 



They are termed Faces of Crystallisation, in order to 

 distinguish them from certain other faces of minerals, 

 which, though they exhibit regular shapes, yet are no crys- 

 tals (. 26.). 



The faces of crystallisation receive particular names, ac- 

 cording to the forms which they limit, as, for instance, 

 Faces of the Rhombohedron, of the Octahedron, &c. They are 

 called Faces, without any nearer determination, if the 

 form to which they belong is understood to be a form of 

 crystallisation. 



