ON THE PRIMITIVE FORM OF CRYSTALS. 343 



so far as tliey have both only one axis symmetrically 

 situated in the solid ; and even if this resemblance 

 had not been strengthened by their having both 

 only one axis of double refraction, it might entitle 

 us to unite them into one class, and thus identify 

 the crystallographic with the optical system, 



The agreement between Mobs' System of Fun- 

 damental Forms, and that which is derived from 

 optical structure, will appear still more striking, if 

 we compare the individual determinations of primi- 

 tive forms which each of them have furnished ; and 

 as the forms which Haiiy has ascribed to several 

 minerals are incompatible with their optical struc- 

 ture, we shall thus be able to estimate the relative 

 values of the French and the German systems of 

 crystallograimy. 



The following Table will point out the deviations 

 of Haiiy's primitive forms from those which I have 

 given in this and a former paper. 



