HISTOBY. OF MINERALOGY. 79 



line forms, much more simple than those of Weiss and 

 Mohs, and published in 1830 a treatise on crystallography, 

 which is regarded as the most learned and complete work 

 we possess on the subject. 



The principles assumed by the Germans have received 

 considerable confirmation from the brilliant optical disco- 

 veries of Sir David Brewster. The system of Mohs, in 

 particular, is generally adopted, and with the discoveries 

 which confirm it, will be explained, in a future page ; his 

 nomenclature of single minerals, however, from being cum- 

 bersome and difficult, has failed. The two electro- chemical 

 systems introduced by Berzelius are conceived to be im- 

 perfect. His first attempt was to class all minerals accord- 

 ing to their electro-positive element, and the elements 

 according to their electro-positive rank ; but the discovery 

 of isomorphism, and the law of equivalents, virtually anni- 

 hilated the system. These celebrated discoveries were, in 

 substance, as above-stated, that certain substances assuming 

 the same crystalline form may be substituted for each other 

 in combination, without affecting the external character of 

 the compound. Hence, since bodies with very different 

 electro-positive elements could not be distinguished from 

 each other, it became impossible to place them in distant 

 parts of the same classification. The second attempt, by 

 the same philosopher, to found a classification on electro- 

 negative qualities, is declared by our able English historian 

 of the sciences, to be no more trustworthy ; for he observes, 

 if the electro-positive elements are isomorphous, the electro- 

 negative elements are sometimes isomorphous "also, and 

 cites the arseniates and phosphates in proof of his assertion. 



As the summary of this brief sketch of the history of the 

 science, it may be stated that the systems hitherto proposed 

 can scarcely be regarded as satisfactory or complete, though 

 we should recommend the reader to study that of Mohs as 

 the theory most generally received. The present state of 

 our knowledge in this, as in other departments of science, is 

 confessedly imperfect ; the labours of the distinguished men 

 whom we have enumerated, are to be regarded as approxi- 

 mations to the truth, rather than as the truth itself; and 

 to borrow the conclusion of that author to whom we are 

 so largely indebted for the information here detailed, "The 



