Abstract
A galvanometer system for the measurement of very small voltages, of the order of 10−11volts, is described and its application to the measurement of feeble radiations with a thermocouple discussed. It has been found that energies of the order of 1/200 of that previously detected by other devices could be measured with the Resonance Radiometer. The effect of the Brownian Movement on the system has been calculated and has been found to be about 1/200 that of the effect on the ordinary galvanometer. An experiment is described for the measurement of the speed of action of thermocouples, and results on the splashed filament type are recorded.

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