158 



electric bulb, but also from ambient light from the sun. 

 The resultant of these two was computed against the standard 

 calibration in air, and presented as percentage of light 

 transmission. 



The hydrophotometer was used primarily in water surrounding 

 sewer outfalls to detect layers of debris-ladden water. Several 

 lowerings of the device were made in Santa Monica Bay well away 

 from the outfall? but no detailed pattern of stations was 

 occupied (Fig, 77), Around the sewer outfalls s, hydrophotometer 

 casts were made at each bacteriological station and from the 

 determinations of light transmission, many valuable profile 

 patterns were produced. In Figure 78., for example 5 the surface 

 portion of the sewage field can easily be recognized, as can 

 the substirface debris layer. In several instances the trans- 

 parency profiles followed closely those plotted from bacteria 

 samples and they were,, therefore,, helpfal in reaching the con= 

 elusion that sedimentation of bacteria in the sea is an impor- 

 tant factor in their disappearariceo 



Transparency in Santa Monica Bay 



The average transparency of the water in Santa Monica Bay 

 as measured by the Secchi disc is shown in Figure 76, , The 

 waters within two miles of shore usually have a transparency 

 of less than 20 feet and in the vicinity of outfalls or streams 

 discharging detrital material into the bay, the readings are 

 normally less than 10 feet. In deeper water and farther from 

 shore, the transparency increases to a maximum of about 45 

 feet. Here the waters originate offshore and have little 



