Daily Variation of Ultra-violet Radiation and its Distribution in the Sky

Abstract

The intensity of the ultra-violet radiation between the wave lengths 2700Å-3150Å (Fig. 1) was measur_??_d with a proper combination of the vacuum Chrom-photo-cell and the glass filter which is transparent enough for shorter wave lengths (Fig. 2). The results of the measurements are as follows:-
(1) The intensity of the U. V. radiation is strongest in the direction towards the sun, and becomes weak with the distance from the sun (Fig. 3 and 4). The U. V. radiation from the area with the radius of 30° around the sun exceeds oneha f of the total U. V. radiation from the whole sky.
(2) The daily variation is very remarkable (Fig. 5). The range of it is larger than that of the direct or scattered sky radiation which includes the whole wave lengths. The effect of the scattering for shorter wave lengths is very remarkable wh_??_n the altitude of the sun is low, as is expected by the theory of Rayleigh. (Fig. 6.)