Id* ■ Parallel of Rome de V Isle's and 



to minerals assuming that crystalline form. But I cannot 

 terminate this sketch better than by the following extract 

 from the Abbe Hauy's Treatise on Mineiaiogy. 



i( In short, Rome de ITsle reduced the study of crystal- 

 lography to principles more exact, and more consistent with 

 observation. He classed together, as much as he was able, 

 crystals of the same nature. From among the different forms 

 belonging to each species he selected one which appeared 

 to him to be the most proper, on account of it3 simplicity, 

 for the primitive form ; and then supposing it to be trun- 

 cated in different manners, he deduced the other forms, and 

 established a certain gradation or series of passages from the 

 primitive form to that of polyedrons, which would scarcely 

 appear to have any connection with it. To the descriptions 

 and figures which he gave of the crystalline forms, he added 

 the mechanical measurement of the principal angles, and 

 he showed (a most essential point) that these angles were 

 constantly the same in each variety. In a word, his crys- 

 tallography is the fruit of immense labour, by its extent ; 

 almost entirely new in its object; and of great value for its 

 utility." (Vol.1, p. 17.) 



The Abbe Haiiy in his Treatise on Mineralogy embraces 

 a far greater extent than Mr. de ITsle. His mineralogy is 

 not only descriptive, but it is physical, chemical, and geo- 

 metrical. In the persuasion that a mineral cannot be well 

 described, nor even in many cases recognized, unless its 

 physical, chemical, and geometrical characters are clearly 

 laid down, the Abbe never omits any one of those charac- 

 ters, when ascertained, and exposes with the most scrupu^ 

 lous exactness every thing relating to them that observation 

 has authenticated. He has bestowed particular attention to 

 the electrical and magnetic phaenomena, and has enriched 

 the science with a multitude of new and curious observa- 

 tions. He attentively examined the property of double re- 

 fraction which several transparent minerals enjoy ; and here 

 again he has extended the boundaries of science. A few 

 minerals were known to possess this property, and the 

 Abbe has discovered it in several where it had never been 

 surmised. 



When we consider that writers on mineralogy have hi- 

 therto grounded their systems exclusively, some on the 

 exterior characters, others on the chemical properties of 

 minerals ; and that the Abbe really has, pursuant to his plan, 

 (see in the beginning of the volume of plaies, La distribution 

 mcthodlqiic des mineraux, par classes, ordres, genres et <?s- 

 pciuS) The methodical distribution of minerals into classes, 



orders, 



