PHYSICAL PROPERTIES OF SEA WATER 



29 



within as narrow spectral bands as possible and has assigned the observed 

 coefficients to distinct wave lengths, but it should be understood that the 

 wave length actually stands for a spectral band of definite width. He 

 has made numerous observations in the shallow waters near islands in the 

 inner part of Juan de Fuca Strait and at four stations in the open oceanic 

 waters off the coast of Washington, and these can be considered typical of 

 coastal and of oceanic water, respectively. Table 4 contains the absorp- 

 tion coefficients of pure water (according to Sawyer) at the wave lengths 

 used by Utterback, the minimum, average, and maximum extinction 

 coefficients observed in oceanic water, and the minimum, average, and 

 maximum coefficients observed in coastal water. The minimum and 

 maximum coefficients have all been computed from the four lowest and the 

 four highest values in each group. In the clearest oceanic water the 

 extinction coefficients were only twice those of pure water, and the aver- 

 age values were four to five times the latter, w^hereas the maximum values 

 were up to ten times as great. In the coastal waters the minimum values 

 were up to sixteen times greater than the absorption coefficients of pure 

 water, the average values were up to twenty-four times as great, and 

 the maximum values were up to thirty-four times as great. The increase 

 of the extinction coefficients, however, varied widely in the different 

 parts of the spectrum and was relatively much greater for shorter wave 

 lengths than for longer ones. 



Table 4 



ABSORPTION COEFFICIENTS PER METER IN PURE WATER AND 

 EXTINCTION COEFFICIENTS IN THE SEA 



(From Utterback's data) 



The great difference between the mean and the maximum values of 

 the extinction coefficients shows that the absorption of sea water varies 

 within very wide limits. In the example presented in table 4 the per- 

 centage variations are about the same in coastal and oceanic waters, and 



