AbstractVisual and photographic observations of the illumination of the sky‐sea horizon, made in light of different wavelengths, indicate an enhanced brightness contrast when the shorter wavelengths are excluded. The effect is most pronounced in the presence of haze, or light mist. When use is made of an analysing filter to modify the relative amounts of polarised light received from sky and sea, the degree of contrast obtainable depends on a number of independent factors,e.g., amount of cloud cover, and state of sea surface that may, or may not, combine to give better visibility of the sky‐sea boundary. Anomalous polarisation effects are frequently observed during early twilight along the anti‐solar path. This work was carried out while with the Kodak Research Laboratories. The paper is issued as Communication No. 1263H from the Kodak Research Laborat