Figure 27-15. Contour map of the function given in formula (59) . 



'«**« = 'tf{?=ij$T? 



+ 



l(x — u) (z — h) 



[ (x - u) 2 + (y- v) 8 ] [ (x - u) 2 + (y - v) 2 + (z-h) *]^ '2 



[(*-i*) 2 + (y-v)« + (*-£)*]*'* 



dudv 



(57) 



If we now compute IH X at the point (o,o,o), measuring x and y in units of h, 

 we get the approximation 



610 



