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268 On the Use of Dejinitmis. of this, was able to apply the term with correctness, after a little experience, to the subject under all its varieties of colour, form, or position.*" By the adoption of such names and definitions it becomes possible to make general assertions concerning the effects of clouds. The possibility of doing this is the condition and the proof of the scientific propriety and value of the nomen- clature just noticed, and of any other. Cuvier, with great philosophical justice, applies this test to shew the absurdity of a classification, and consequently of a nomenclature, which had been adopted in another branch of science. Zoology. " Gmelin*" he says, " by putting the lamantin in the genus of morses^ and the sirene in that of angiiilles^ had rendered any general proposition with re- gard to their organisation impossible."" To define a lamantin to be or not to be a morse, does not merely make one pro- position true instead of another, but decides whether there shall be any true proposition at all : and to know whether it is to be so defined, we must first know the analogies of or- ganisation which it is the business of scientific language to express. In another branch of natural history, the inconvenience which arises from the assumption that any one may construct or appropriate names, without regulating himself by any general views, has been most oppressively felt. We speak of Mineralogy. Here the general principles of classification being still in utter obscurity and confusion, there has been nothing to prevent any one from giving new names to new specimens, without ascertaining whether they were related to minerals already named, as another genus, another species, an- other variety, or, it may be, another fragment of the same mass. It may easily be supposed that this unrestrained licence has filled our mineralogical books with a mob of names, desti- tute of arrangement and subordination, and consequently of use. Even eminent philosophers have not abstained from adding to the croud. Sir J. Herschel has called one substance Leucocyclite^ because with polarised light it gives black and white rings : Sir David Brewster has named another mineral Tesselite^ because examined in the same way it appears to be constructed of several pieces of different properties joined