The Absorption of Light by Fog

Measurements between two stations 0.4 km apart with a thermocouple and galvanometer and with spectrograms, properly calibrated, of the absorption of light by fog for wave-lengths from 0.4 to 3{μ} showed that the absorption increased slightly with decrease in wave-length, but hardly enough to indicate that red light is appreciably better than blue light for the purpose of penetrating fog. For a fairly dense fog, such that in daylight dark colored objects at about 0.6 km could barely be be seen, the distances necessary to reduce the light to 10^-2 of its original value were about 710, 843, 910, 970, 980 and 980 meters for wave-lengths 0.4, 0.5, 0.6, 1.0, 2.0 and 3.0{μ}, respectively.