LAWS OF DECREMENT. 



351 





THE OBLIQUE RHOMBIC PRISM. 



Its elements. 

 Fig. 353. 



The inclination of P on M, or M', fig. 317, varies 

 in different minerals ; call it /,. 

 Inclination of M on M' also varies in different 

 minerals, and may be called / 2 . 

 Plane angle/* a d, fig. 351, may be called A v . 

 Let g a e, g a c?, d a e, be the three sides 

 of a spherical triangle, whose angles would 

 be 90, /,, and \ I 2 . The side g a d, which 

 is \ A i9 may be thus found, 



sm. \ v 

 Plane angley a e, or d a e, may be called A 2 . 



This angle is the hypothenuse of the tri- 

 angle from which we have derived the pre- 

 ceding formula, and may therefore be thus 

 known, 



cot 7 cot 7 * 



cos A - 



CObya 2 



Terminal edges equal. 

 Lateral edges equal. 





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