370 APPENDIX CALCULATION OF THE 



RHOMBOID. 



The general equation may therefore be thus ex- 

 pressed, 



P <1 



or, dividing all the terms by D, it may be reduced 



to this general form, 



Fig. 360. 



Let the plane a d e, fig. 360, represent one of the 

 planes belonging to class jfo whose indices are p, q, 

 and r ; and let 



o e ~ p. 



o d = , 



o a =. r; 

 the equation of this plane will then be, 



But as the line 0/at which the two planes of mod./ 

 intersect each other, is parallel to the axis of the 

 rhomboid, and passes through one of its superior 

 edges, it might obviously be on the surface of some 



