IQS QnCTystaUography* 



other is necessary for continuing this chain and arranging 

 the different hnks of it. 



I trust that this long discussion will be forgiven. T 

 thought it necessary, because it appeared to nie that at no 

 tin)e has the influence been sufficiently ackno\vledged,which 

 mineralogy ouglit to have on a well -arranged mt-thod ; and 

 because, if there are cases in which the mineralogist cannot 

 refrain from saying to the chemist, Make me acquainted 

 tvit/i the substance nhick you have analysed, — there are 

 others in which the chemist, if he is cautious, ought to 

 say to the mineralogist^ Make me acquabited tvith the sub- 

 stance which I have analysed. 



M. Vauquelin, who adds to dexterity of operating a great 

 accuracy of reasoning, ha's proved more than once, that he 

 did not regard th£ consequences inferred from the geometry 

 of crystals as useless in assisting us to fix the term at which 

 the analysis ought to begin. Placed by circumstances 

 beside each other, we have frequently consulted together 

 on the subject of our inquiries, and the results which 

 we attained, by two methods of interrogating nature 

 so different, were mutually of service as guarantees by 

 their conformity. I feel strongly the advantages which 

 this cooperation has produced, and I am anxious that it 

 should be publicly known, that it is m the Ecole des Mines 

 in PVance that chemistry and crystallography, so long se- 

 parated, have contracted a strict alliance, which bids fair 

 to be of long duration. 



If we now resume the comparison between the me- 

 thods of botanists and those of mineralogists, we may 

 observe that the former are entirely founded on charac- 

 ters furnished by observation of the external form, but 

 the latter having a necessary connexion with the internal 

 organization, which is constant in all the individuals of 

 one and the same species, each of them may serve as a 

 conmion model, in order to paint as if at a single stroke 

 the entire species. 



In the mmeral kingdom, on the contrary, in which the 

 external characters undergo continual variations, in which 

 even the best defined forms are only evanescent disguises, 

 nothing that speaks to the eye can serve as a foundation to 

 the method. It belongs to analysis to lay this founda- 

 tion, and to regulate the order of classification, making use 

 on all occasions of the light afforded by crystallography. 

 But this object once attained, the observer must be able to 

 ascertain the substances classified by methods independent 



of 



