330 HISTOEY OF MINERALOGY. 



peculiarities of Symmetry, such, for instance, as that of the plagihedral 

 faces of quartz, and other minerals. 



The introduction of an arrangement of crystalline forms into systems, 

 according to their degree of symmetry, was a step which was rather 

 founded on a distinct and comprehensive perception of mathematical 

 relations, than on an acquaintance with experimental facts, beyond 

 what earlier mineralogists had possessed. This arrangement was, how 

 ever, remarkably confirmed by some of the properties of minerals which 

 attracted notice about the time now spoken of, as we shall see in the 

 next chapter. 



CHAPTER V. 



RECEPTION AND CONFIRMATION OF THE DISTINCTION OF SYSTEMS 



OF CRYSTALLIZATION. 



T\IFFUSION OF THE DISTINCTION OF SYSTEMS. The distinction of 

 U systems of crystallization was so far founded on obviously true 

 views, that it was speedily adopted by most mineralogists. I need not 

 dwell on the steps by which this took place. Mr. Haidinger's transla- 

 tion of Mohs was a principal occasion of its introduction in England. 

 As an indication of dates, bearing on this subject, perhaps I may be 

 allowed to notice, that there appeared in the Philosophical Transac- 

 tions for 1825, A General Method of Calculating the Angels of Crystal*. 

 which I had written, and in which I referred only to Hatty's views ; 

 but that in 1826, 1 I published a Memoir On the Classification of Crys- 

 talline Combinations, founded on the methods of Weiss and Mohs, 

 especially the latter ; with which I had in the mean time become 

 acquainted, and which appeared to me to contain their own evidence 

 and recommendation. General methods, such as was attempted in the 

 Memoir just quoted, are part of that process in the history of sciences, 

 by which, when the principles are once established, the mathematical 

 operation of deducing their consequences is made more and more 

 general and symmetrical : which we have seen already exemplified in 

 the history of celestial mechanics after the time of Newton. It does 

 not enter into our plan, to dwell upon the various steps in this wav 



1 Camb. Trans, vol. ii. p. 391. 



