During descents into the sea to depths of over 1400 feet Beebe observed that the color of the water illuminated by the sun was a pure blue and measured the candle power of the illumination at various depths down to 800 feet. At 800 feet the spectrum was a narrow band centering at about wave length 520mμ. Using the light absorption coefficients of sea water as measured in the laboratory and the Raman-Einstein-Smoluchowski theory of the scattering of light in liquids, it is found that the spectrum of the daylight at 800 feet in the sea has a maximum brightness at about 500mμ; this agrees well enough with the observation.
The calculated candle powers of the undersea daylight illumination were much greater than the observed values. The assumption that the absorption in the sea below 200 feet was the same as the laboratory measured absorption and in the surface layers down to 200 feet was about 5 times the laboratory value led to good agreement between the observed and calculated candlepowers at all depths. The surface layer absorption would be accounted for if 25 millionths of the volume of the surface water was occupied by opaque material.
© 1932 Optical Society of AmericaFull Article | PDF Article
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