Abstract
Leaving the summit, where we had done observations before whose result we have already reported, we removed the observation tent to the top of a cliff very near to the seashore. The cliff is about 40 m. in height, and faces the Pacific Ocean to southern direction.
(a) When we observe the sea surface from such a low level, it seems that the light which comes to the observer from the sea is consisted of sky light reflected by wavelets of the sea surface. Therefore, the condition of its polarization depends mainly upon the nature of the sky light which is reflected by the sea surface. And consequently, in this case, the polarization phenomena can not sufficiently be explained merely by the theory of Rayleigh's scattering as in the former case, and so we have proposed that it is necessary to take into account the Brewster's law of reflection too to explain the polarization.
(b) In the case of clear skies, degrees and planes of polarization of light reflected by the sea surface varies parallel to those of the sky light from the zone at an altitude of about 10° in the same direction. In the case of overcast skies, the planes of polarization are always vertical for all directions.
The range of variation in degrees of polarization is 0.1_??_0.4 for the light from the sea, and 0.0_??_0.7 for that from the sky.
(c) As to the relation to bearings, such conspicuous correlation as seen in the preceding chapter can not be found, except in the case of clear and calm weather.
(d) The degree of polarization changes abruptly at the sea horizon. Thus the contrast between the sky and sea surface can be increa_??_ed by using the polarized light in most cases, except in the direction at right angles to the vertical plane passing through the sun. This seems to be an important fact concerning the contribution of the Polaroid to the improvement of visibility at sea.
