Figure 5. Temperature and depth indicators for the car 

 containing the hydrophotometer. 



apart (fig. 3-E), These discs made it possible to sample a 

 very narrow cross-section of the water at the same level as 

 the hydrophotometer. The samples were pumped to the 

 surface for filtering and analysis. 



OBSERVATIONAL PROCEDURE 



The observational procedure was to run the cart and 

 instruments vertically through the water column every half- 

 hour, beginning with the cart on the bottom. Slightly less 

 than 3 minutes (at a speed of 4 inches per second) was re- 

 quired for the traverse from bottom to surface and for making 

 a continuous recording of light transmission (turbidity) and 

 temperature. After the run was completed, the cart was 

 again lowered to the bottom and left there until the start of 

 the next run. 



Water samples could be taken at any depth. If taken 

 while the cart was moving, the length of time required for 

 the water to be pumped through the hose had to be considered 

 in determining the depth from which the sample came. 

 Sampling while the cart was moving provided a continuous 

 hydrophotometer trace with water samples every few feet, 

 and made possible a direct comparison of the data. However, 

 the water samples were taken normally on separate casts, 

 the cart being stopped at 5-foot intervals for pumping of the 

 biological sample. The turbidity of the water was obtained 

 on these runs as well. 



11 



