BASE, AND ITS MODIFICATIONS. 



Class z. Edges of the base replaced by two planes. 

 The new figures would be more acute octahedrons, 

 with rhombic bases. 



The unequal angles at which the primary planes 

 incline to each other at the edges B and C, sufficiently 

 distinguish this class of octahedrons from the pre- 

 ceding classes. 



ITS MODIFICATIONS. 



Primary form. A right square prism. 



The individuals of this class will differ from each 

 other in the comparative length of the edges G and B. 



Modifications. 



Class a. Solid angles replaced by single planes 

 whose edges are generally isosceles triangles. 



But they are not necessarily always so. 



For if the decrements in height be to those in 

 breadth in exactly the same ratio that the terminal 

 edge of the prism bears to its height, the truncating 

 planes on the angles will be equilateral triangles, 

 and those on the edges of the summit would, under 

 similar circumstances, be tangent planes. 



