Abstract
An integrating actinometer for ultraviolet radiation with a photo-tube and a filter was constructed which is operated by a 100V A. C. power supply. The principle of operation is charging up the photo-electric current due to incident radiant energy in a condenser and then discharging and forming an impulse to operate a relay counter. Experiments on the linearity of the response, errors due to power supply fluctuations, temperature effects of the instrument and the absolute sensitivity were carried out. The general performance has been very satisfactory. Above all, the stability against the fluctuations of power supply is the essential merit of this instrument.
Using these instruments ultraviolet solar and sky radiation falling on a horizontal plane were measured in two different ranges of wave-length, the one about 3, 700A and the other about 3, 400A. The observed results are compared with those of Robitzsch pyrheliometer. According to this result, the extinction of ultraviolet solar and sky radiation due to cloudy weather is stronger in the shorter range of wave-length than in the longer, and moreover, the extinction of total, that is, including visible and infrared radiation is by far the strongest, naturally because of the strong absorption of infrared radiation due to water vapour.
