238 HISTORY OF MINERALOGY. 



hedron. This division, as I have already said, errs 

 both by excess and defect, for some of these primary 

 forms might be made derivatives from others ; and 

 no solid reason could be assigned why they were 

 not. Thus the cube may be derived from the tetra- 

 hedron, by truncating the edges ; and the rhombic 

 dodecahedron again from the cube, by truncating 

 its edges; while the square pyramid could not be 

 legitimately identified with the derivative of any 

 of these forms ; for if we were to derive it from the 

 rhombic prism, why should the acute angles always 

 suffer decrements corresponding in a certain way 

 to those of the obtuse angles, as they must do in 

 order to give rise to a square pyramid ? 



The introduction of the method of reference to 

 Systems of Crystallization has been a subject of 

 controversy, some ascribing this valuable step to 

 Weiss, and some to Mohsl It appears, I think, 

 on the whole, that Weiss first published works in 

 which the method is employed ; but that Mohs, by 

 applying it to all the known species of minerals, 

 has had the merit of making it the basis of real 

 crystallography. Weiss, in 1809, published a Dis- 

 sertation On the mode of investigating the princi- 

 pal geometrical character of crystalline forms, in 

 which he says 4 , "No part, line, or quantity, is so 

 important as the axis; no consideration is more 

 essential or of a higher order than the relation of 



3 Edin. Phil Trans. 1823, vols. xv. and xvi. 

 < pp. 16, 42. 



