CLASSIFICATION, 



281 



substances (the simple ones are not numerous enough to re- 

 quire a systematic nomenclature), there is one property, the 

 chemical composition, which is of itself sufficient to distinguish 

 the Kind ; and is (with certain reservations not yet thoroughly 

 understood) a sure mark of all the other properties of the com- 

 pound. All that was needful, therefore, was to make the name 

 of every compound express, on the first hearing, its chemical 

 composition ; that is, to form the name of the compound, in 

 some uniform manner, from the names of the simple substances 

 which enter into it as elements. This was done, most skilfully 

 and successfully, by the French chemists. The only thing left 

 unexpressed by them was the exact proportion in which the 

 elements were combined; and even this, since the establish- 

 ment of the atomic theory, it has been found possible to express 

 by a simple adaptation of their phraseology. 



But where the characters which must be taken into consi- 

 deration in order sufficiently to designate the Kind, are too 

 numerous to be all signified in the derivation of the name, 

 and where no one of them is of such preponderant importance 

 as to justify its being singled out to be so indicated, we may 

 avail ourselves of a subsidiary resource. Though we cannot 

 indicate the distinctive properties of the Kind, we may indi- 

 cate its nearest natural affinities, by incorporating into its 

 name the name of the proximate natural group of which it is 

 one of the species. On this principle is founded the admirable 

 binary nomenclature of botany and zoology. In this nomen- 

 clature the name of every species consists of the name of the 

 genus, or natural group next above it, with a word added to 

 distinguish the particular species. The last portion of the 

 compound name is sometimes taken from some one of the 

 peculiarities in which that species differs from others of the 

 genus ; as Clematis integrifolia, Potentilla alba, Viola palustris, 

 Artemisia vulgaris ; sometimes from a circumstance of an 

 historical nature, as Narcissus poeticus, Potentilla tormentilla 

 (indicating that the plant was formerly known by the latter 

 name), Exacum Candollii (from the fact that De Candolle was 

 its first discoverer) ; and sometimes the word is purely con- 

 ventional, as Thlaspi bursa-pastoris, Ranunculus thora; it is 



