A new radiometer

A radiometer, which measures directly the flux of radiant energy integrated throughout a hemisphere, is described. It consists of a very light electrical resistance thermometer element which is suspended, thermally isolated in high vacuum, behind an infra-red transmitting window. The front is blackened to receive the radiation, while the back is a bright mirror to prevent absorption or emission. The element comes into thermal equilibrium at a temperature T °K with an incoming radiation stream of energy F . Then F = σ T 4 , with small corrections for heat leakage. The determination of these corrections is the only calibration which is necessary. The radiometer is robust, reasonably rapid in response, and is not affected by external airflow. For these reasons it is especially suitable for radiative flux measurements in the upper air from an aircraft. It may have other uses in heating and ventilating problems or wherever low-temperature radiation is important.