52 



THE UNIVERSITY SCIENCE BULLETIN. 



U 



-J — -X 



a 6 



2 9 <S 



FIG.l 



r(x,y,u)=o,y=o 

 y 



_I I I L. 



8 C 9 \ 2 



£ \y 6 a 



FIG. II 



r(x.y,u)=o,u^o , (b) /so/a fed 



