ITS MODIFICATIONS. 127 



Class k. Edges replaced by two planes. 



The new figures would be contained within 48 

 triangular planes. 



It may be remarked that the secondary forms be- 

 longing to the four preceding classes of primary 

 forms, are nearly similar to each other. And, with 

 the exception of the tetrahedron, each primary form 

 is found to be also a secondary form to each of the 

 other primary. 



The table of secondary forms, which will be found 

 at the end of the tables of modifications, exhibits the 

 relation to each other of each of the preceding classes 

 of secondary forms. 



BASE, AND ITS MODIFICATIONS. 



Primary form. The octahedron with a square base. 



The individuals belonging to this class will differ 

 from each other in the inclination of P on P", and 

 consequently of P on P'. 



Modifications. 



Class a. Terminal solid angles replaced by tan- 

 gent planes. 



As this modification contains only two parallel 

 planes, those planes can never efface the primary 

 planes and produce a solid. The same observation 



