14 



PROCEEDINGS OF THE NATIONAL MUSEUM 



of a Secchi disc provides a good absolute measure for water clarity 

 and one that is taken easily as a routine oceanographic measurement. 

 At the same time, apparent water color may be recorded in the Forel 

 scale. The BCF records and files both measurements on their punch 

 cards. Photometric depth is another measure of water clarity made 

 on oceanographic cruises, but it demands much more complicated 

 instrumentation and the figures vary with intensity of illumination. 

 It may be useful to record the presence of flotsam, large masses of weed, 

 ice, or other floating debris. Some observations suggest that marine 

 life and birds may be attracted locally to foreign matter in the water. 



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Figure 7. — Bar graphs of abundance of black-footed albatross (shaded) and sooty terns 

 (white) in birds per mile seen at various surface water temperatures on Cromwell cruises. 



On the day sheets several changes should be made. All observa- 

 tions for the pilot program were made in a single octant of the world, 

 but other sets of observations may be made in several octants or a 

 cruise track may cross the equator or a 90° meridian and thus require 

 two octant codes for the same day. For this reason octant columns 

 (37 and 46) should be added to sunrise position and sunset position 

 fields. As a result, the fields for sunrise and sunset time and number 

 of observers would be moved two columns to the right. It has not 

 been feasible to make these octant additions in the Smithsonian 

 program. 



