LAWS OF DECREMENT. 



33$ 



THE OCTAHEDRON WITH A RHOMBIC BASE. 



Fig. 345. 





Its dements. 



The inclination of the planes at the obtuse ter- 

 minal edges may be called /, . 

 Inclination of the planes at the acute terminal 

 edges may be called /,. 



Inclination of the planes at the edges of the 

 base may be called / 3 . 



Plane angles at the summit, being called A tj 

 may be thus found, 



cot -^ cot. 



cos A = 



R 



A spherical triangle is marked on the 

 upper part of the above figure, the angles 

 of which are 90, \ 1 ^ and \ / 2 , and of 

 which the required side b a c is the hypo- 

 thenuse, which is found by the preceding 

 formula. 



The two spherical triangles marked at 

 the base of the figure, will give the follow- 

 ing formulae; the required side being in 

 each instance the hypothenuse of the as- 

 sumed triangle. 



