MINERALOGICAL SYSTEMS. QQ 



When treating of a fpecies or of a variety, he refers his His method of 

 reader to the table where the figure of that fpecies or variety «lefcnptioa. 

 is to be found, and he then enumerates every thing relating to 

 minerals aduming that cryflalline form: But I cannot termi- 

 nate this iketch better than by the following extracl from the 

 Abb^ Hauy's treatife on mineralogy. 



*' In (hort Romede L'Ifle reduced the ftudy of cryftallogra- Quotation 

 phy to principles more exa(5l and more confident with obfer- "j^'j^g""^^^ 

 vation. He clalTed together, as much as he was able, cryftals De rifle's la- 

 of the fame nature. From among the different forms belong- °°""* 

 ing to each fpecies, he feleded one which appeared to him to 

 be the moft proper, on account of its fimplicity, for the primi- 

 tive form, and then fuppofing it to be truncated in different 

 manners, he deduced the other forms, and efiablifiied a cer- 

 tain gradation or feries of paffages from the primitive form to 

 that of polyedrons which would fcarcely appear to have any 

 connexion with it. To the defcriptions and figures which he 

 gave of the cryfialline forms, he added the mechanical mea- 

 furement of the principal angles, and he (lie wed (a molletTen- 

 tial point) that thefe angles were conflantly the fame In each 

 variety. In a word, his cryftallography is the fruit of immenfe 

 labour by its extent; almoft entirely new in its obje61, and of 

 great value for its utility." (Vol I. page J 7.) 



The Abb^ Hauy in his treatife on mineralogy embraces a The mineralogy- 

 far greater extent than Mr. de L'Ifle. His mineralogy is not °f ^^uy is not 



1 1 r • • I • • 1^1 1 -1 1 . . nierely defcrip - 



only deicriptive, butitis phylical, chymical and geometrical, tive, but phyfi^ 

 In the perfualion that a mineral cannot be well defcribed, nor "^' chemical 

 even in many cafes recognized, unlefs its phyfical, chemical,^" geometnca, 

 and geometrical charaders are clearly laid down, the Abb6 

 never omits any one of thofe charaders when afcertained, and 

 expofes with the moft fcrupulousexaflnefs every thing relating 

 to them that obfervation has authenticated. He has beftowed Eledlricity. 

 particular attention to the eledrical and magnetic phenomena, Magnetifm. 

 and has enriched the fcience with a multitude of new and cu- 

 rious obiervations. He attehtively examined the property of Double refrac- 

 double refradion, which feveral tranfparent minerals enjoy ;^^°^* 

 and here again he has extended the boundaries of fcience. A 

 few minerals were known to poflefs this property, and the 

 Abb^ has difcovered it in feveral where it had never been 

 furtnifed. 



When we confider that writers on mineralogy have hitherto Hauy has ex- 

 grounded their fyftems exduftvelj/, fome on the exterior cha- thetabUudes°^ 



rapiers. 



