LAWS OF DECREMENT. 



353 



OBLIQUE RHOMBIC PRISM. 



lei to the diagonal g , and touching the solid angle 

 at m. For the line fr is evidently in a plane per- 

 pendicular tofd, and if the modifying planes we are 

 considering were to be produced, they would cut fm 

 and/r proportionally. The ratio of fh tofr, is thus 

 found. 



R 



m sin. | ^ t : cos. (/ 3 90"). 



Fig. 355. 



The unit for determining the laws of decrement 

 producing the planes of classes /and g is the ratio of 

 a b to a e, fig. 355, when the angle fa d is obtuse, or 



2 Y 



