downstream stagnation streamline intersected the trailing edge of the body. 

 Such an observation resulted from the visible reversed flows on the upper 

 and lower foil surfaces or the absence thereof in the region of the trailing 

 edge of the body. Therefore^ determination of the satisfaction or the vio- 

 lation of the Kutta-Joukowski condition is possible; the degree of accuracy 

 depends on the accuracy with which the conductors were positioned on the 

 surface of the foil. Such a determination would undoubtedly employ the 

 definition of separation point and reversed flow discussed earlier and the 

 lighting scheme as sketched in Figure 11. An experiment using essentially 

 this same method for specifying the position of separation is described 

 in Eeference 9- 



For instance^ in the surface of a plastic foil shape^ wire conductors 

 which can be energized separately are placed so that they are parallel to 

 the trailing edge and spaced^ e.g.^ 0.010 in. apart; then the point of 

 separation could be determined on this foil to an accuracy of not less than] 

 0.010 in. Such accuracy is achieved by observing between which two wires 

 the velocity gradient is normal to the surface and changes sign. 



ACKNOWLEDCMEM'S 



The author wishes to express his gratitude to Dr. F. R. Kama for 

 stimulating his initial interest in the hydrogen-bubble technique. 



Specific thanks also go to Mr. John Coon^, who greatly assisted in the 

 establishment of the technique at the Model Basin. 



Last, but certainly not least, many thanks for the helpful suggestions, 

 endless patience, and expert photographic experience which were made avail- 

 able to the author by Mr. Berkley Ball of the David Taylor Model Basin. 



25 



