Pickwell 



the bubbles remain thus exposed for long periods, neither protruding 

 further, nor retracting. 



Correlation of bubble size with increasing float size is possible 

 only within very broad limits as shown in Fig. 3. The range in size 

 of expelled bubbles for a single pneumatophore may be greater than 

 an order of magnitude. The total observed number of expelled bub- 

 bles and of pneumatophores within arbitrarily chosen increments of 

 size is presented in Fig. 4. The maximum observed number of bub- 

 bles expelled by a single float was 9. 



Close observations from DEEPSTAR at mid- morning, mid- 

 afternoon, and in the early morning during October, November, and 

 December, 1966, have shown the pneumatophores of intact colonies 

 of Nanomia bi.juga to be inflated whenever observed. It is presumed 

 that the float is fully inflated at all times and, therefore, always a 

 potentially effective sound scatterer. 



An inflated pneumatophore, although small, is also an effective 

 light reflector. This is clearly seen in Fig. 5 where an intact colony 

 of Nanomia bijuga is shown in a characteristic feeding position with 

 tentacles extended. The glistening float is situated at the uppermost 

 terminus of the colony where it serves as a sort of gas-filled trim 

 tank providing neutral buoyancy for the motionless colony. 



DISCUSSION 



The standard means of determining resonant frequency, fp, for 

 a bubble of known radius, R, at any given depth is by the formula 



where fr is in cycles per second, R is in centimeters, Y is the ratio 

 of specific heat of the gas at constant pressure to its specific heat at 

 constant volume (this equals 1. 4 for both air and carbon monoxide), 

 Po is the static pressure of the gas within the bubble in dynes/ cm^, 

 and p is the specific gravity of the medium, usually taken to be 1. 025 

 gm/ cm^ for sea water. •'"^ 



Equation (1) may be reduced to the more convenient, approximate 

 form 



f =id+12)* (2) 



r R 



where fr is in kc/ s, d is the depth in meters, and the radius, R, is 

 in mm. 



Recently the Russians, Andreyeva and Chindinova, when deal- 

 ing with fish swimbladders, have added the shear factor of Lebedeva, 

 I^Q, to equation (1) to give 



18 



385 



