Murthy 



Now 





x -j a ( 1 » _ y -v S /I 



z -f 



so that 



d / 1 \ - y -V , . 



x -* 



dh, . dh 



1 z -f 1 



a* 



7 + 



3 ar 



and considering first S with 

 6 1 + 



V = V' 



= b + 5 hj (m 



we have 



a (JL) . -y + b + a hl ({Y) + <(,- { ) -^. + * ( ..f)-^ 



*,+ |"(x-{) 2 + |y -b-« hj (f'f')| 2 + (z-f) Z J 

 Assume now that (x, y, z) lies just outside S so that 

 y = b + 5 h ( xV) + « 



where e is a small positive quantity « 6 

 Then 



a l 



ah. 



"ST^ 7 ; F~ i. In 3/2 



(x - u + 



*h (x'z 1 ) + e - 5h (ST) 



2 + (z - O 2 



which is of 0( 6 ) as e — >-0 , unless x — ?• £ and z — ^ f when 

 it is of 0( -4— ) • 



In the limiting case when 6 also — > it can be shown that 



-.— (— ) — ► 2tt 6 (x - S) 5 (z - D + 0( 8 ) 

 a n r 



232 



