reverberation time. The quality factor characterizes the 

 cavity plus the contained liquid. The above value refers to 

 the cavity filled with nominally pure water. However, it 

 should be noted that any contained bubbles on the walls will 

 tend to produce a low estimate of the Q which would apply 

 for completely degassed water. 



A cylindrical cavity in the form of a shallow pan was 

 also investigated. This has the advantage that the free 

 surface and bottom represent the major fraction of the 

 boundary, thus minimizing the area of rigid surface. Good 

 Q factors were obtained, since bubbles do not tend to stick 

 to the bottom and have little effect at the free surface. 

 Bubbles which cling to the cylindrical surface are so far 

 removed from the center that their effect is negligible, 

 since the main reflections take place between top and 

 bottom of the cavity. The main difficulty was that the 

 slightest vibration caused surface waves to be set up. 

 This created difficulties in tuning the cavity, as well as 

 irregularities in the way the sound died out, when the 

 generator was disconnected. 



The spherical cavities were obtained by cutting off the 

 neck of commercially available, round-bottom boiling 

 flasks made of Pyrex. Higher Q's can be obtained with 

 these bottles than by any other readily available method, 

 but they suffered from the same limitations as the cylin- 

 drical containers to an even more marked degree. The 

 opening in the flasks is so small that cleaning the inside 

 surface is virtually impossible. This type of resonator 

 has been used extensively for research on pure liquids and 

 gases, but was considered unsuited for measurements on 

 sea water with the naturally occurring particulate matter 

 suspended in it. The cylindrical resonators were likewise 

 given up for the same reasons. 



12 



