"Reflections on some Mirier ah gical Systems, 2S& 



among the colours) effects the translation of a mineral from 

 one species to that of another, as it is that which, super- 

 added to the first, forms the fourth characteristic difference, 

 while the other minerals always remain in the same species 

 as before. — It is the last pound under which the camel suc« 

 cumbs. 



Here is a second example of the very serious incon- 

 veniences arising from making the species depend on any 

 fixed number of characters. Form is a character, crystal- 

 lization is comprehended in forms. M.Werner admits the 

 prism only where there exist certain proportions between 

 its height and its breadth ; if we diminish the former, the 

 prism becomes, a table. The prism and table are considered 

 as making two different species of primitive forms. Take 

 a crystal of calcareous spar in a hexahedral prism, and an- 

 other crystal of the same in a hexahedral table; here is a 

 different primary specific character in these two specimens 

 of calcareous spar. Suppose the table very near becoming 

 a prism, and the prism approaching very near to the table ; 

 and suppose the one translucid and the other ©pake; add 

 two specific characters not less insignificant than these two > 

 and behold a new species at very little expense. But, had 

 the causes which determine crystallization added some mo- 

 lecules of carbonate of lime to the calcareous spar, in the 

 direction of the axis of the prism which was considered a 

 table, it would have been saved from this forced separation 

 from its equals. 



In establishing a subspecies, if the liberty of choosing two 

 or three for the number of characters by which the ob- 

 server decides, leave any influence to the particular value 

 of each character, it is necessary that this value should rest 

 on a solid basis ; otherwise we risk the danger of making 

 arbitrary dispositions, and the same mineral may be found 

 belonging to as many different species as there will be per- 

 sons who shall examine it. M. Werner, indeed, has di- 

 stinguished some characters by the order of importance iii 

 the determination of the species, as well as in the diagnosis 

 of minerals. He gives sometimes to the specific gravity, 

 sometimes to the colour, more value than to the greater part 

 of the other characters, t have seized every opportunity 

 to acquire clear ideas on this subject, either in consulting 

 M. Werner himself, or addressing those who had profited 

 most by his instructions ; and all that I have been able to 

 learn amounts only to this, That the value of a character 

 varies from one species to another : thus, then, to decide 

 on it, it is necessary to know the species, that is to say, in 



Vol. 36. No. 150. Oct. 1810. T algebraic 



