The effect of low temperatures on the sensitivity of radiometers

The behavior of radiometers at low temperatures, besides being of some interest to the theoretical physicist,(2) is of considerable importance to one desiring to carry radiant energy measurements to an extreme limit. Various workers have already pushed the sensitivity of such instruments as the thermocouple, radio micrometer, and radiometer into the region in which Brownian movement begins to mask observations so that any great gain in the sensitivity of existing instruments must come from some change in technique rather than from mere refinement of our instruments