A new method of determining the radiation constant

Abstract

According to stefan's law the rate of radiation of energy from a full radiator in surroundings at a temperature of absolute zero is σ θ 4 ergs per cm. 2 per sec., where θ is the absolute temperature of the radiator. If the radiator be in surroundings which are themselves full radiators, but at absolute temperature θ 1 , the rate of loss of energy by radiation is taken to be σ( θ 4 - θ 1 4 ). The classical determination of the constant σ is due to Kurlbaum, who used a surface bolometer with a platinum-black surface. The rise of temperature of the bolometer when exposed to the radiation from an approximately full radiator or "black body" was observed. The radiation was then cut off, and an equal rise of temperature was produced by increasing the main current in the bolometer. It was assumed that the energy received per second from the radiator in the first case was equal to the energy received per second from the increase of current in the second ease. The resulting value of σ was 5·33 x 10 -5 ergs per cm. 2 per sec. per deg. 4 , or 5·33 x 10 -12 watts per cm. 2 per deg. 4 .