66 TERMINOLOGY. . 79- 



History (. 5.). But Natural History endeavours to de- 

 termine the relations under which crystalline forms of cer- 

 tain dimensions appear in the individuals of the same spe- 

 cies, or come into connexion with each other. These re- 

 searches not only form part of the peculiar object of Na- 

 tural History ; but this science derives the greatest advan- 

 tage from them in its farther developement. 



. 79. DERIVATION. 



The method employed in Natural History for 

 determining the kind and the relations of crystal- 

 line forms, which occur in the individuals of the 

 same species, or come into connexion with each 

 other, is called the Derivation. 



To derive one simple form from another, is to shew- 

 how, according to a certain general rule, it arises, or is 

 produced from it. The processes of derivation consist in 

 geometrical constructions, which are not gratuitously ima- 

 gined, but deduced from observation ; and their correct- 

 ness and applicability, though evident from their very ori- 

 gin, is thoroughly confirmed by the exactness with which 

 the phenomena in nature can be explained. 



There are several of these rules or methods of proceed- 

 ing by which the derivation can be effected. Of these 

 different methods, those must be selected which will ap- 

 ply to the quality of the form from which the derivation 

 is to start, and which is termed the given form. The pro- 

 duct of derivation is called the derived form. The derived 

 and given forms are either of the same, or of different kinds. 

 The derived form is a simple form, like the given one ; or, 

 should this not be the case, it must be resolved into two or 

 more simple forms. The derived form having thus been 

 developed, the relations existing between this and the 

 given one are to be determined. 



