350 HISTOEY OF MINERALOGY. 



more trustworthy ? Was not the necessity of an entire change of sys- 

 tern, a proof that the ground, whatever that was, on which the electro- 

 chemical principle was adopted, was an unfounded assumption ? And, 

 in fact, do we not find that the same argument which was allowed to 

 be fatal to the First System of Berzelius, applies in exactly the same 

 manner against the Second ? If the electro-positive elements be often 

 isomorphous, are not the electro-negative elements sometimes isonior- 

 phous also ? for instance, the arsenic and phosphoric acids. But to go 

 further, what is the ground on which the electro-chemical arrangement 

 is adopted? Granted that the electrical relations of bodies are im- 

 portant ; but how do we come to know that these relations have any- 

 thing to do with mineralogy ? How does it appear that on them, prin- 

 cipally, depend those external properties which mineralogy must study? 

 How does it appear that because sulphur is the electro-negative part 

 of one body, and an acid the electro-negative part of another, these 

 two elements similarly affect the compounds ? How does it appear 

 that there is any analogy whatever in their functions ? We allow that 

 the composition must, in some way, determine the classified place of 

 the mineral, but why in this way ? 



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 in every case ; although, considering the usual discrepan- 

 cies of analyses of minerals, this objection must make all pure chemi- 

 cal systems useless. But I may observe, that mineralogists have not 

 yet determined what characters are sufficiently affixed 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 iso- 

 morphism. The tenet of the constancy of the angle is rendered doubt- 

 ful 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 mineralogists 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 characters, 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 



6 Jahres Berir.ht. viii. 188. 



