316 APPENDIX-^ CALCULATION OF THE 



REGULAR OCTAHEDRON 



Fig. 337. 



The law of an intermediary decrement producing 

 any modification belonging to class d, may be thus 

 discovered. 



Let/ o- h i, fig. 337, be one of the planes of that 

 class, and let its inclination on P, and on P', which 

 is supposed to be known, be called I 6 and I 7 . 



The symbol to represent this plane would be 

 (B P b' q B'r bs). 



p representing the number of molecules contained 

 in the line a g of the above fig. 



q .... ah, 



r ..../, 



v . . . . a i. 



The spherical triangle marked on the fig. at P P', 

 will give the plane angles a gf and a g h, which we 

 may denote by A 4 'and A 5 , by means of the following 

 formulae. 



sin. f A^ = 



^i4[(180 / 6 )+Jj -f (18(F--/ 7 ) 3 cos4[ (180 / 6 )+/,-- (180 J 7 )] 

 sin. (180 J 6 ) sin./,. 



1/ 



sin. (180 / 7 ) sin. / 



