368 APPENDIX CALCULATION OF THE 



RHOMBOIT*. 



deduce our required law of decrement be one of those 

 which appears on the angle at O. 



There are, as may be seen in the tables, three 

 classes of modifications produced by these decre- 

 ments, being classes f, z, and I. 



The distinction between these three classes has 

 been already pointed out in the table of modifications 

 of the rhomboid, and in p. 279, where their several 

 relations to the theory of decrements are given. 



The general symbol representing one of the planes 

 at the angle O, belonging to either of these modifi- 

 cations, is (D' q b"r Dp), and the particular value of 

 the indices may be discovered, in relation to any 

 particular modification belonging to either class, by 

 measuring the inclination to the two primary planes 

 adjacent to the edge b", of the plane represented by 

 the above symbol ; and finding the plane angles of 

 the defect adjacent to the edge b", by means of a 

 spherical triangle, and thence deducing the ratio of 

 the edges of the defect in the manner already de- 

 scribed. 



The indices of the individual modifications belong- 

 ing to classy will be found in a constant ratio to each 

 other. This results from the condition that the edge 

 at which the modifying planes "intersect each other 

 shall be parallel to the axis of the rhomboid. 



Let the index p be > 7, and q ^> r. 



The relations between p, q^ and r, may be thus 

 stated, 



p = q (7-1) = q r. 



a = 1+ V *H-1 _ P 

 2 ' r' 



