340 HISTORY OF MINERALOGY. 



ture. We may classify without reference to chemistry ; but if we do 

 so, it is only that we may assert chemical propositions with reference 

 to our classification. 



But, as we have already attempted to show, we not only may, but 

 we must classify, by other than chemical characters, in order to be 

 able to make our classification the basis of chemical knowledge. In 



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order to assert chemical truths concerning bodies, we must have the 

 bodies known by some tests not chemical. The chemist cannot assert 

 that Arragonite does or does not contain Strontia, except the mine- 

 ralogist can tell him whether any given specimen is or is not Arragonite. 

 If chemistry be called upon to supply the definitions as. well as the 

 doctrines of mineralogy, the science can only consist of identical pro- 

 positions. 



Yet chemistry has been much employed in mineralogical classifica- 

 tions, and, it is generally believed, with advantage to the science : 

 How is this consistent with what has been said ? 



To this the answer is, that when this has been done with advantage, 



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the authority of external characters, as well as of chemical constitution, 

 has really been brought into play. We have two sets of properties to 

 compare, chemical and physical ; to exhibit the connexion of these is 

 the object of scientific mineralogy. And though this connexion would 

 be most distinctly asserted, if we could keep the two sets of properties 

 distinct, yet it may be brought into view in a great degree, by classifi- 

 cations in which both are referred to as guides. Since the governing- 

 principle of the attempts at classification is the conviction that the 

 chemical constitution and the physical properties have a definite rela- 

 tion to each other, we appear entitled to use both kinds of evidence, 

 in proportion as we can best obtain each ; and then the general con- 

 sistency and convenience of our system will be the security for its con- 

 taining substantial knowledge, though this be not presented in a rigor- 

 ously logical or systematic form. 



Such mixed systems of classification, resting partly on chemical and 

 partly on physical characters, naturally appeared as the earliest 

 attempts in this way, before the two members of the subject had been 

 clearly separated in men's minds ; and these systems, therefore, we 

 must first give an account of. 



Sect. 2. Mixed Systems of Classification. 



Early Systems. The first attempts at classifying minerals went upon 

 the ground of those differences of general aspect which had beer 



