TABLE QF SECONDARY FORMS. 



217 



Secondary forms. 



The rhomboid 



CONTAINED WITHIN EIGHT 

 PLANES. 



The regular octahedron. 



The octahedron with a 

 square base 



The octahedron with a 

 rectangular base ...... 



The octahedron with a 

 rhombic base 



How they may be derived. 



From the rhomboid, Modi- 

 fication, by c, g, &, or m. 



From the cube, Mod. a. 



........ regular tetrahedron. 



Modification o, when the 

 secondary planes first touch 

 each other on the edges of 

 the tetrahedron. In this 

 state of the figure, four of 

 the octahedral planes are 

 obviously the primary 

 planes of the tetrahedron. 



rhombic dodeca- 

 hedron. Modification e. 



octahedron with a 

 square base, Modification 



...... right square prism, 



Modification u, or c. 



right rectangular 

 prism, by the concurrence 

 of Modifications b and c. 



the right rhombic 

 prism, when Modification 

 , or c, is combined with 

 four of the primary planes. 



octahedron with a 

 rectangular base, Modifi- 

 cation A, , A:, or /. 



octahedron with a 

 rhombic base, Modification 



or z. 



right rectangular 

 prism, Modification a. 



right rhombic prism^ 

 Modification # rf or e. 



