230 PROCEEDINGS OP THE AMERICAN ACADEMY 



Also 



a a a 



= 2 n Q^cdu -!- Q,hdb + Q^cdc] = 2 J--^ = 4j|f , 



'i 00 00 



and concequently ^ is a homogeneous function of a, h, c of degree — 1. 

 ■ ••• a'^Qa + ^'Qb + '^'Qc^-hQ- 



= 1 1 {X- - a^) Q^ + {f - I') Q, + {^ - c"-) ^,} . 

 Within the shell 



F = I {x'^Qa^+fQ,, + ^^^0,) - 2 9P (^. + If. + ^.) «iS«i + «^°«t- 

 At the surface the const. 



= 2 Qpa^^a, + ^ <? ; 



•••^=i2^«. ^^^-1"^ + l2^^ V F 



