, MOLECULES. 51 



This theory may, by analogy, be extended to the 

 form of molecules of every class of octahedron. 



For we may conceive the molecules of all the irre- 

 gular octahedrons to be parallelepipeds, whose least 

 molecular attraction is in the direction of their diagonal 

 planes. 



Thus the molecules of octahedrons with a square, a 

 rectangular, and a rhombic base, would be square, 

 rectangular, and rhombic prisms respectively; the 

 dimensions of such molecules being proportional re- 

 spectively to the edges of the base and to the axis of 

 each particular octahedron. 



According to the view here taken, the following 

 table will exhibit the form of the molecules belong- 

 ing to each of the classes of primary forms. 



The cube 



rhombic dodecahedron , J 



all quadrangular prisms molecules, similar prisms. 



-\ Proportional 



r i i in dimensions 



octahedron with a square base 5 mo e ? u e> a to the edges 



rectangular C molecule, a rectan- I ^ !L ^ S ^' 



base I gular prism f , , - 



rhombic base $ lecule,a rhombic ^ocSe- 



t P nsm dron,respec- 



J lively. 



rhomboid molecule, a similar rhomboid 



, . C molecule, an equilateral triangular 



hexagonal prism } . 



Having thus advanced a new theory of molecules 

 in opposition to one that had been long established, 

 and possibly without a much better claim to general 



the class of /danes of composition, a term which Mr. W. Phillips has 

 plied to those cleavage planes which result from cleavages parallel 

 secondary planes only. 



