Cb) 



Corttini, Nellson, and 

 Altinbiiek (1983) 



(d) 



Ktnnedy ond Falcon (19655 



(f) 

 Dingier (1975) 

 ' lob 

 • field 



* .X;!^- 



2a 

 D 



Figure 5. A/D as function of 2a/D, from various observers. 



The straight line in each plot is given by equation (10) 



22 



