Peterson 
Thus it appears that the probability of bubbles existing in the towing 
basin water immediately prior to a run, is extremely remote. 
Now, if in fact free stream bubbles are necessary for cavita- 
tion inception, then a dichotomy exists between the basin and the wa- 
ter tunnel studies. The measured free stream bubbles in the water 
tunnel canaccain for the visually observed cavities but not the acou= 
stic determination of cavitation inception. The towing basin acoustic 
determination of inception agreed with the basin high speed movies and 
the water tunnel acoustic inception determination. As already pointed 
out, the probability of free gas bubbles existing in the basin water is 
extremely remote although the dissolved gas content was approximat- 
ely 100 percent saturated. 
On the basis of these studies, it appears that the free stream 
bubbles contributed to the production of the visibly observed cavities 
on the headforms but were not necessary for the generation of those 
cavities that produced acoustic radiation during collapse. Justas 
numerable investigators have concluded before, the results of the 
studies reported here can also best be explained by the existence of 
a hydrophobic particle with gas trapped within a crevice ( [27] - [29]). 
There has been a considerable amount of research performed by in- 
vestigators in other research disciplinesthat has significantly increas- 
ed the plausibility of this postulated nucleation mechanism. Within the 
cavitation literature available to this writer, it appears that these 
new related research results have not been discussed. Therefore, the 
next section will deal specifically with this related research. 
STABLE HYDROPHOBIC PARTICLES IN THE WATER 
The concept of cavity nucleation by a hydrophobic particle in water has 
long been the subject of considerable discussion. The basic hypothesis 
is that a small quantity of gas is trapped in a crevice of a particle and 
stabilized by the surface tension of the water because the particle it- 
self is hydrophobic. This theory was first advanced by Harvey, etal 
[27, 28, 29] and has most recently been reviewed by Apfel [30] .A 
number of recent experiments have been carried out that indicate the 
hydrophobic particle may play an important role in the cavity nucle- 
ation process in water [30 - 33] . In keeping with the nature of this 
paper, a survey of the literature on this subject will not be attempted 
but rather only those references most pertinent to the discussion will 
be considered. One of the most detailed experiments was carried out 
by Greenspan and Tschiegg [32] with an acoustically excited cylindric- 
al resonator. They found that the cavitation threshold for unfiltered 
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