HYDROPHOTOMETER 



Light transmission was measured with a hydropho- 

 tometer (fig. 2) developed by J. Tyler, of Scripps Institution 

 of Oceanography Visibility Laboratory. The theory of such 

 instruments is discussed by Tyler and Preisendorfer (1962)^ 

 and Holmes (1957). The device measured light intensity 

 impinging on a Weston 856-RR photocell. The light was 

 transmitted along a 1/2-meter path from a 6-volt light bulb 

 (General Electric 964). The filament voltage was monitored 

 by a Cohu electronic galvanometer, and a variable power 

 supply was used for calibration. Baffles were placed along 

 the light path to eliminate ambient light. The photocell 

 output was fed to the pen drive of a Leeds and Northrup 

 Speedomax recorder. The hydrophotometer was adjusted 



HYDROPHOTOMETER 



THERMISTOR 



Figure 2. Equipment rack on tower used to measure light transmission, temperature, and 

 depth, and to sample plankton in the water. 



