CLEAVAGE, 



65 



The relation of the tetrahedron to the octahedron 

 in reference to the theory of cubic molecules, may be 

 explained in the following manner. 



The Abbe Haiiy's theory, it will be recollected, 

 supposes that if the tetrahedron obtained by cleavage 

 from the octahedron, were to be successively reduced 

 to an octahedron and four still smaller tetrahedrons, 

 we should at length arrive at a tetrahedron consisting 

 of four single tetrahedral molecules enclosing only an 

 octahedral space, instead of an octahedral solid. 



But according to the structure assigned to the 

 octahedron by the theory of cubic molecules, that 

 figure is an entire solid; and the smallest tetra- 

 hedron that can be imagined to exist, will contain 

 an octahedral solid, and would be reduced to an 

 octahedron by the removal of four cubic molecules 

 from its four solid angles, and not of four tetrahedrons. 





Fig. 95. 







Fig. 96. 



Let fig. 96 be supposed to represent the smallest 

 octahedron that can be imagined to exist, formed of 

 seven cubic molecules, and let fig. 95 represent a 



i 



