tlJ? On Crystallography. 



We have adopted this nomenclature wherever the know- 

 ledge we have acquired would admit of it; and amidst a 

 crowd of examples which we could quote, in order to 

 prove how much mineralogy has gained by this adoption, 

 we shall confine ourselves to what is furnished by the word 

 spar. Originally several species of minerals which had a 

 lamellousand opal-like [chatoyavt) texture were united under 

 this head. Thus there were calcareous spars, heavy spars, 

 fliLor sparsy shining spar<i, he. At the lime when the 

 different bodies designated by this word composed a single 

 genus, as seems to have been the case at the origin of the 

 science, it was the method that was more in fault than the 

 nomenclature, by identifying species essentially different 

 from each other. Subsequently, however, the;>e same bodies, 

 having been better known, were separated from each other 

 and placed in different genera, or even in different classes, 

 and nevertheless they were not allowed to preserve their 

 common denomination of spar; and the inevitable alter- 

 native occurred, cither to parcel out a genus in order to 

 disperse its members, which is contrary to all the principles 

 of the method, or to confound under one and the same 

 name, genera which in other respects had nothing common, 

 which IS not less opposite to the principles of a good no- 

 menclature. And as if there was not enough of confusion 

 occasioned by the spars of the ancient mineralogy, the 

 abuse of this word has, as it were, multiplied in modern 

 denominations^ and hence we have boracic spars, adaman- 

 tine spars, &c. The language of modern chemistry, by 

 suppressing the word spar in the acidiferous substances, has 

 given a kind of signal-post for extending the same reform 

 lo some of the earthy substances which still remained ob- 

 scured by this erroneous appellation*. 



As to the names of these last substances, they ought 

 to be founded, at least for the present, on considerations 

 foreign to the chemical nature of bodies; and it is even to 

 be presumed that we shall not be yet able to refer them to 

 the results of analysis, always supposing that we are not 

 stopped by the prolixity of those which should be applied 

 to substances composed of three or four earths intimately 

 combined with each other. Whatever may be the case, 

 names are wanted which could serve durinj^ an indefinite 

 tinje, and this was one reason for also making in this part 



• We have preserved this word in the denominatif»n of fehhpnr onljt 

 which has been now too generally used not to be respected, and about which 

 there can be oo ambiguity, because it is no longer employed on any other 

 occasion. 



