With a quartz spectrograph, sodium hydride quartz photoelectric cell and quadrant electrometer, measurements were made in the ultraviolet spectrum region λ4000 to 2500A of the light absorption coefficients of pure water and sea water and of the molecular absorption coefficients of aqueous solutions of the principle salts in the sea, namely, NaCl, KCl, MgCl2, MgSO4 and CaSO4. The transparency of the sea water declines rapidly with decreasing wave length in the ultraviolet becoming quite small below λ3000A. From λ3400 to 3000A, CaSO4 contributes about half to the absorption of sea water, H2O about a fourth and the other salts the rest; from λ3000 to 2500A, MgCl2, CaSO4 and H2O each contribute roughly a third, the other salts giving relatively little absorption. There is a close correspondence between the falling off in the transparency of the sea with decreasing wave length in the ultra violet and the spectral energy curve of sunlight. This, together with the very similar correspondence in the case of the transparency of the atmosphere permits the suggestion that the actinic effects of sunlight may have played a part, perhaps more important than has been heretofore recognized, in the constitution of the sea and the air.
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