574 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



Fig. 13 — A Schlieren photograph of an ultrasonic quartz radiator shows the presence of 

 amplitude variations similar to those of Fig. 12. (After Osterhammel.) 



Fig. 14 — Plane waves dififracted by a knife edge become cylindrical in the shadow region. 



/ = 9 KC. 



remarkable similarity in the general appearance of the patterns. Immedi- 

 ately along the axis of the radiators, one observes quite large amplitude 



