regime on the body, namely an attached boundary layer in which these small, 

 essentially stationary, bubbles grow, they conclude, by a process of air 

 diffusion. Subsequently, these bubbles, when of sufficient size, would be 

 "stripped off" to "feed" the downstream macroscopic cavitation seen by the 

 eye. It will be noticed that at the location of the observed small bubbles 

 the local pressure is actually above the fluid vapor pressure, hence, 

 vaporous growth would be impossible there. Presumably, truly microscopic 

 bubbles could grow further upstream near the minimum pressure point, but 

 these were not observable with the photographic technique used. Parkin 

 and Kermeen also stressed that travelling-bubble cavitation did not occur 

 in their tests readily because the new facility had a "resorber" which 

 prevented comparatively large freestream bubbles (the nuclei for the 

 travelling bubbles) from being recirculated, and thus, that this type of 

 cavitation had a true boundary-layer origin. 



This work had a vital, energizing effect on cavitation research and 

 the physical ideas presented were used as the basis for a number of 

 theories of the scaling effect (e.g., van der Walle 1962, Holl and 

 Kornhauser 1969, among others) . These theories incorporated the idea of a 

 microbubble stabilized on the surface of a body so that growth by gas 

 diffusion could occur until some critical size was achieved when downstream 

 transport into the flow would take place. Further refinements in bubble 

 dynamics accounting for thermodynamic effects (Plesset and Zwick 1955) and 

 growth by oscillating pressure fields, i.e., "rectified diffusion" (Hsieh 

 and Plesset 1961), did not provide additional mechanisms sufficient to 

 explain the large scale effect. Before turning to some of these data we 

 mention two additional concepts dealing with inception on smooth surfaces. 



The first of these, due to Daily and Johnson, pointed out that the 

 turbulent fluctuations in fully-developed pipe flow can also lead to 

 cavitation. (This observation has been expanded subsequently by Arndt and 

 others to deal with jet cavitation, but this is not the subject of the 

 present work.) In the meantime, Ripken and Killen were able to demonstrate 

 in certain types of cavitation the importance of the undissolved gas, i.e., 

 the microbubble "nuclei" within the flow. In addition, they published size 



