(n , n 3 , n,) = (1, 2-, 1) 



(1, 1, 1) 

 (1, 2, 1) 

 (2, 1, 1) 



Before a consistent data collection could be undertaken, 

 it was necessary to find a method for keeping the side walls 

 of the cavity clean. Of the several methods which were 

 tried, a squeegee mounted on a thin tube appeared the most 

 satisfactory. This device made it possible to insure abso- 

 lutely clean walls, with the only drawback that of the un- 

 avoidable disturbance in the water. 



Evaluation of Oxygen and Plankton 



Special precautions were taken in drawing plankton and 

 oxygen samples from the water in the cavity. A 50-ml 

 pipette with the tip removed was used to draw the samples, 

 and it was rinsed clean and thoroughly wetted before each 

 sampling. The plankton was drawn from the center of the 

 cavity, where its influence on the acoustic properties of 

 the sea water would be most pronounced. To avoid the 

 inclusion of water too far removed from the center, only 

 about 1 ounce was drawn. The sample was immediately 

 preserved by adding 2 cc of 40 per cent formaldehyde solu- 

 tion to the sampling jar. 



The plankton count was obtained by shaking the sample 

 thoroughly, filling a Sedgwick-Rafter counting cell with 

 the sample, and counting the organisms by lOOx in a micro- 

 scope. 



In drawing oxygen samples, great care was taken not 

 to work bubbles into the water at any time. The pipette 

 was allowed to fill by itself without suction, and the tip 

 was touched to the inside of the O2 bottle held at a slant, 

 so that the pipette would empty slowly and smoothly. The 

 preservation and titration of the sample followed the stand- 

 ard procedure used in connection with Winkler determina- 

 tion of oxygen. Standard 1 50-ml oxygen sample bottles 

 with ground glass stoppers were used throughout. 



64 



