Pr fessor H. S. Hele-Shaw 



[Feb. 10, 



I will now tiike a more striking case. If, instead of a circular 

 body, we bad a flat plate, tbe turbulent nature of tbe flow is evidently 

 very great, as you will see from tbe view (Fig. 13), which is a photo- 

 graph of the actual flow under these conditions, made visible by very 



Fig. 13. 



fine air bubbles, and showing water at rest in the clear space behind 

 the obstacle. 



We can, however, take steps to reduce this turbulence, and you now 

 see on the second screen the flow by means of apparatus which time 



