a ex' was determined on this basis. The attenuation with 

 the flooded glass rod suspended in the center of the cavity 

 was the same as without the glass rod, within the accuracy 

 of the measurements. By sighting along the reverberation 

 curves in figures 5 to 7, it can be seen that they are not 

 absolutely straight. The straight part with the smallest 

 attenuation is, however, long enough to give a reasonably 

 accurate determination of the reverberation time. The 

 points obtained have been plotted in figure 15, and the 

 vertical dashed line in this figure corresponds to the diam- 

 eter of a free bubble resonant at 5100 c/s. The glass rod 

 will undoubtedly change the resonance frequency as well 

 as the attenuation from the corresponding values for a 

 free bubble, but the agreement is still quite good. 



A vibrating bubble radiates a spherical sound field, 

 which will represent a scattering loss if the bubble is 

 situated in a plane progressive sound field. This same 

 spherical sound field will not cause a loss when measure- 

 ments are carried out in a cavity with the bubble suspended 

 in the center, but it will cause a change in the resonance 

 frequency of the cavity. 



The Sea Water Data 



The attenuation values as evaluated from the measure- 

 ments on the sea water samples are contained in figures 16 

 to 32. The group 16 to 2 pertain to measurements for 

 mode 1-1-1; group 21 to 2 5, to mode 2-1-1; and group 26 

 to 30, to mode 1-2-1. It will be recalled that the three 

 different modes correspond to the following frequency bands: 

 5. to 5. 5, 6. 5 to 6. 7, and 7. 8 to 7. 9 kc/s (the exact value 

 of the resonant frequency for each mode being dependent 

 mainly upon the depth of water). Figure 31 illustrates the 

 variation of attenuation with time for a series of samples 

 taken over a period of about 16 hours. Figure 32 is a 

 sequence of measurements taken in rapid succession for 

 given samples over a period of about 100 minutes. 



75 



