16 ART. ?.. — AICHT AND TANAKADATE : THEORY OF 



+Z dl 



or 



This coincides with (4'), i.e. the I'esult when we neglect the 

 angular diameter of the drop. 



6. General nature of the intensity curve. 



It will be advantageous to consider first tlie maxima and 

 minima of F as compared with those of /^, and then to discuss 

 the general character, and finally proceed to the numerical cal- 

 culation of F, In the expression (4') in § 4 put xx=z, then 



- y. >i> 



Thus the maxima and minima of F are given hy 





J ^Vw^-^'^^|/^'(>^^+^^)|=o 



Or, putting the mean value of -\/{x(ff-z'^ in the integral, we 

 arrive at the approximate relation 



For smaller values of d, especially at the first maximum, f^ 



has no symmetry on both sides of the maxima and minima 

 (see PI. I.) ; so that the first maximum of F receives a small 

 displacement towards 6 = as compai-ed with /-. This displace- 

 ment becomes smaller and smaller for other maxima and minima. 

 For larger values of 0, as /-' is nearly symmetrical on both sides, 

 the maxima and minima approximately coincide with those of 



