On the Penetration of Daylight into the Sea

Abstract

During descents into the sea to depths of over 1,400 feet Beebe observed that the color of the water during the midday hours of a sunny day was a pure blue and measured the candle‐power of the illumination at various depths down to 800 feet (Beebe, Bull. New York Zoological Society, v. 33, 201, 1930). At 800 feet the spectrum was a narrow band centering about wave‐length 520μμ The absorption of light in the visible and ultraviolet portions of the spectrum by samples of pure sea‐water taken from the Gulf Stream, the Atlantic and Pacific oceans, and the Caribbean Sea far from land have been measured in the Laboratory (Hulburt, J. Opt. Soc. Amer., v. 13, 553, 1926, and v. 17, 15, 1928). Using the Laboratory absorption‐coefficients 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 500μμ. This agrees with Beebe's result probably within the error of the observations.