

BASE, AND ITS MODIFICATIONS. 



Primary form. An octahedron with a rectangular 

 base. 



In this figure the broad planes P P', meet at the 

 edge of the base at a more obtuse angle than the nar- 

 row ones MM 7 . The edge D may therefore be 

 denominated the obtuse edge of the base, and the 

 edge F the acute edge; or they may be termed the 

 greater and lesser edges of the base. 



The individuals belonging to this class of primary 

 forms will differ from each other in the inclination 

 of Pon P', or ofM on M'. 



Modifications. 



Class . Terminal solid angles replaced by single 

 planes. 



Class b. Terminal solid angles replaced by two 

 planes, resting on the broad planes. 



