1 903.] JMtctfic Waves round a Conducting Obstacle . 67 



Similarly the value of ?i, for which a group of terms of S 7 has a value 

 different from zero, is given by 



and remembering that -^ is always very small, the corresponding 

 value of n is /<] as in the- previous case. Now, when wi-f i : sin a, 



sin 2 a 



ta " *" = 



and is, therefore, to the order required, zero, cos \,, being unity, 



hence 



S 7 = 

 therefore 



2 sin 



The value of ~ is, therefore, for values of V which are not near 



0/^=0 



to or TT, given by 



& a 



ihe terms of highest order only being retained. Now 



where 



^ 

 that is, 



to the order adopted, and 



a 



or 



whieh for values of ^ not near to zero, becomes on putting i\ = 



' Koj. 8oe. I'l-or.. 1 vol. 71, p. 251. 



