306 APPENDIX CALCULATION OF THE 



CUBE. 



angle g h d, the inclination of the primary to the 

 secondary plane. 



The planes belonging to classes b and c of the 

 modifications of the cube, result from simple and 

 mixed decrements. 



Let the inclination of P on the plane b adjacent to 

 it, or on the plane c which rests on the edge between 

 P' and P",* be measured and called /, . 



If p, as before, be used to represent the decrement 

 in breadth, and q the decrement in height, then 



p- R 



q tang. ( ISO -/, ) 



Intermediary decrements. 



The general symbol representing a single plane 

 belonging to class d, would be (B P B //7 q B'r). And 

 the law of decrement producing a particular plane 

 of that class, would be discovered by finding the 

 values of />, q, and r, in relation to that particular 

 plane. 



Let us suppose q ^> r. 



If we refer to the tables of modifications, we shall 

 observe that two of the planes which have the d 

 placed upon them, rest on the edge between P and P 7 . 



Let that which inclines most on P', be measured on 

 P and P'. 



Let Pond / 2 . 

 P 1 ..d = I 3 . 



Let the plane angle of the defect corresponding to 

 i a c, fig. 329, be called A , , and that corresponding 

 to i a b of the same fig. be called A z . 



* See the tables of modifications whenever the classes are referred to. 



