of certain Crystals. 63 



prism is equal in area to each rectangular side of the prism, 

 so as to present equal resistance, according to the hypothesis, 

 then the triangular faces will be nearer to the centre in the 

 proportion of three to four, so that the attractions will not be 

 equal as the hypothesis would require. 



A third hypothesis of M. Prechtl is, that the degree of 

 compressibility may be such that each particle will be sur- 

 rounded by six others, giving it the form of a cube, which, it 

 must be admitted, is a very possible supposition. 



AH further application of the same hypothesis is precluded 

 by M. Prechtl, by denying that one particle can be surrounded 

 by more than six others; although in fact it is most evident, 

 that any sphere when not compressed will be surrounded by 

 twice that number, and consequently by a slight degree of 

 compression will be converted into a dodecahedron, according 

 to the most probable hypothesis of simple compression. 



