352 



APPENDIX- 



-CALCULATION OF THE 



OBLIQUE RHOMBIC PRISM. 



The inclination of the oblique diagonal a g, to an 

 edge a e, being called / 3 , may be thus found, 



cos. I = 



cos " 

 sin. i 



The angle g a c is the third side of the 

 triangle already used. 



Ratio of a terminal to a lateral edge can be 

 known only by means of secondary planes. 



Its units of comparison. 



Let us suppose the ratio of y : ae :: m : n :: 1 : 



m 



The unit of comparison in reference to the decre- 

 ments producing the planes of classes a and c, is the 

 ratio of half an oblique diagonal a h to a lateral edge 

 a e, which may be thus found. 



/_._T> T A i cos. -^ A , 



Ji 



Therefore a h : a e :: m cos. \ A v : n R. 

 Fig. 354. 



The unit for determining the decrements producing 

 those planes belonging to class e, of which the repre- 

 sentative symbol is E, is the ratio of \ a horizontal 

 diagonal^" h to the linear drawn from the solid angle 

 aty perpendicularly on r m ; the line r m being paral- 



