472 BELL SYSTEM TECHNICAL JOURNAL 



for a circle of unit illumination of radius R are 





(9) 



where /i is the first order Bessel function. In this particular subject 

 all components of a given wave length have equal amplitudes; and the 



Mimm 



Fig. 4 — Array of field components. 



amplitudes may therefore be plotted as a function of wave length alone, 

 as in Fig. 5. The curve illustrates the rapidity with which the ampli- 

 tudes fall off for the higher order components in a subject of this nature. 



