LAWS OF DECREMENT. 319 



REGULAR OCTAHEDRON. 



Decrements on the edges of the regular octahedron. 

 Fig. 339. 



The inclination of one of the planes of class fa on 

 the primary plane adjacent to it, being- known and 

 called / 8 , the angle a e d y fig. 339, becomes 



(180 J 8 ). 



andfle : ad :: sin. (7 8 /) sin. (180 / 8 ) :: p : q, 

 which will give the law of decrement producing the 

 particular plane we have measured. 





