as a Braiich of Natural History, ^c. ^25 



being incapable to characterize or define by itself a mineral, or 

 a mineral species. But the same objection might equally be 

 brought to bear against all the specific characters employed in 

 zoology and botany. No naturalist has ever thought of charac- 

 terizing a species by a single character ; but, according to the 

 method of gradual description or definition used in natural his- 

 tory, a single character may often be employed to distinguish 

 a given species in its genus, a genus in its order, an order in it* 

 class, and that is all that is required. 



§ 28. Fourthly, it has generally been thought necessary to 

 give to the definition of the characters a degree of mathematical 

 precision and exactness similar to that which is required in natural 

 philosophy, an opinion that has often prevented the use of such 

 characters, which, when taken in their common acceptation, would 

 have proved equally useful and convenient for the description 

 and the distinction of minerals. For instance, the character of 

 solubility in water, which, in the minerals commonly called 

 salts, was, when taken in the proper limits of its usual accepta- 

 tion, a very good distinctive character, and even an important 

 one, by its being closely allied to a number of equally distinctive 

 physical as well as chemical properties ; this character has been 

 given up on account of other bodies essentially different from 

 the so called salts by their various properties, being also, in the 

 strict sense of the word, soluble in water, such as calcareous 

 spar, gypsum, and sulphate of barytes. This too great nicety, 

 for so it may be called in regard to the purposes of natural his- 

 tory, takes its origin in a want of discrimination between the 

 purpose and the wants of this science and those of the exact and 

 abstract sciences, such as natural philosophy and chemistry. In 

 these last mentioned sciences, the object is to find and ascertain 

 positive and absolute truths, while in natural history, as far at 

 least as relates to classification, it is to find differential or rela- 

 tive qualities, and in that case a minute and mathematical pre- 

 cision, is not required for comparative characters, when the limits 

 into which the allegation of such characters is to be understood 

 has been clearly defined. Thus, when we say that, by solubility 

 in water, is meant that property of a mineral by which it is sen- 

 sibly dissolved by a small quantity of water, (less than twenty 

 times the weight of the mineral), we obtain a sufficiently accurate 



JANUARY — MARCH 1832, Q 



