Reflection of Heat Radiation by Sea Surface

Abstract

(1) Introduction.
In considering the heat balance in the atmosphere, it is very important to know the exact value of the reflecting power of the atmospheric radiation by the sea surface, which covers about three fourthes of the area of the whole surface of the earth. Thus, in this preliminary paper, we shall report the method and the result of the measurement, though it is as yet rough. The measurement was done at the seashore of Tôkyô Bay in the last spring.
(2) Method of observation.
As a matter of course, it is desirable to measure the reflection of the atmospheric radiation directly, but it being so difficult, owing to the change of the state of the sky, that some artificial heat source was provisionally used in this observation.
In the figure^*, H is this heat source. It is warm water contained in a chemical flask, the diameter of which is 13.3cm. The surface of the flask was blackened with lamp-black so as to emit black body radiation corresponding to the temperature of the warm water. It is apparent that the energy _??_stribution with respect to the wave length of the radiation emitted from this artificial heat source is different from that of the actual atmospheric radiation, but as the temperature of the water is in the interval between 50°-100°C, it is supposed that the result obtained by the artificial heat source holds for the atmospheric radiation also.
In the same figure, M is a parabolic mirror which was spattered by alluminium in order to reflect the heat radiation almost perfectly. Diameter of the mirror is 30cm. and the focal length is 15cm.
J is a thermojunction of the compensation type, the surface of which is blackened with lamp-black, and G is a galvanometer, inner resistance of which is 11.4 ohm, critical damping resistance 13 ohm, period 4.8 second, and sensitivity 4×10^-9 A and 1.0×10^-7 V.
The thermojunction and the mirror were installed in a wooden box. The aperture of this box was so designed that it is somewhat smaller than the solid angle which subtends the ice-box I, explained below, at the thermojunction as vertex at 25 meter distance from this ice-box, and hence the radiation of the sky around this ice-box was perfectly shaded when the heat source was screened by this ice-box.
The glass, as is well known, is not transparent to the heat radiation, so that the window of the bulb of the thermojunction facing the mirror was made of rock-salt which is known to be transparent to heat radiation in the wave length interval of the atmospheric radiation under consideration. Unfortunately, the rock-salt is apt to deliquesce and looks dim by the vapour in the atmosphere, so that the surface of this rock-salt window was coated by a thin film of polystirol which is very transparent to heat radiation also.
As the zero point of the deflection of the galvanometer, the reading of the scale when the ice-box I was set just in front of the heat source was used. The heat source was thus perfectly screened.
This ice-box I was made of tin-plate, the size of which is about 75×75cm., and it was filled with smashed ice. The outer surface of it was painted with zinc-black so as to emit the black radiation corresponding to the temperature 273°C.