REFORM OF MINERALOGICAL SYSTEMS. 273 



I do not dwell on the remark which Berzelius 

 himself 6 makes on Nordenskiold's system ; that it 

 assumes a perfect knowledge of the composition m 

 every case ; although, considering the usual discre- 

 pancies of analyses of minerals, this objection must 

 make all pure chemical systems useless. But I may 

 observe, that mineralogists have not yet determined 

 what characters are sufficiently fixed to determine 

 a species of minerals. We have seen that the ancient 

 notion of the composition of a species, has been 

 unsettled by the discovery of isomorphism. The 

 tenet of the constancy of the angle is rendered 

 doubtful by cases of plesiomorphism. The optical 

 properties, which are so closely connected with the 

 crystalline, are still so imperfectly known, that they 

 are subject to changes which appear capricious and 

 arbitrary. Both the chemical and the optical mine- 

 ralogists have constantly, of late, found occasion to 

 separate species which had been united, and to bring 

 together those which had been divided. Everything 

 shows that, in this science, we have our classification 

 still to begin. The detection of that fixity of cha- 

 racters, on which a right establishment of species 

 must rest, is not yet complete, great as the progress 

 is which we have made, by acquiring a knowledge 

 of the laws of crystallization and of definite chemi- 

 cal constitution. Our ignorance may surprize us; 

 but it may diminish our surprize to recollect, that 

 the knowledge which we seek is that of the laws of 

 the physical constitution of all bodies whatever ; for 



6 Jakrex Bericht. viii. 188. 

 VOL . III. T 



