290 



G. H. BRYAN. 



r/2 



— ^ (2 ^'*') ^ A '^ — ?r r — u ,ç 



-r-TT (4 V~) = J'^ ^'^i^ 1^'i'^ 



— ^ (i -w /') = 2 2^ Z- — ■ tfi s — v'^s — u V {r -}- /) 

 The équations of energy equilibrinm give 



W 



= W~] 



= [uv\ 



[X2] n [.] 

 [^2] [/] H 



[2AT]H[r + /] 



[r^] H 



[2XJT W[.r + /] 

 [X2] [r] 



[72] [q 

 [2xr] H H 



[r] H 

 [^] [s-] 



(5) 



We notice the foUowing results. 



(1) The mean value [/«'] does uot necessarily vanish. The condi- 

 tion of its vauishing reduces to 



[•^•] j [^] [^Y^] + ['•] [!■'-] I - :i [^] m [xn = 



This is satisfied in particular by 



[XZ] = and [.<?] = 

 as we should expect from gênerai considérations. 



