A New Pyrheliometer and The Standard of Solor Radiation

Abstract

A New pyrheliometer was constructed for measuring the total radiation from sun and sky falling on a horizontal plane. It consists of a special symmetrical type thermopile mounted in a case under a hemispherical glass cover. Characteristics of the pyrheliometer are as follows ; (1) the change of sensitivity according to the direction of radiation follows cosine low; (2) the drift of zero point due to selfheating is within 1% of the indication; (3) the sensitivity is 120 millivolto per watt per centimeter square. (=8.37 millivolts per gram calorie per minute per centimeter square.) As the result of calibrations of the thermopile by our large black body furnace, the sensitivity of the thermopile changed slightly according to the temperature of the black body. In order to established the standard of solor radiation, the sensitivity of thermopiles at the color temperature of the sun was determined from the extrapolation of the certificated value by the black body arid the standard pyrheliometer was calibrated in sunshine against above thermopiles.