Previous formulas for the design of radiation thermopiles to be used with a Thomson galvanometer are summarized and new formulas for the design of thermopiles for use with D'Arsonval galvanometers are developed.
A design of thermopile is described in which the cold junctions almost entirely surround the hot junctions thus reducing drifts. In this design, each element is constructed as a separate unit and when all are completed they are simply stacked up and fastened together with one screw, thereby minimizing the danger of breakage. The whole thermopile fits into a cubical evacuated case only 10 mm on an edge and, being so small, it can be used directly in front of an elliptical mirror which forms a small hot image, in some cases increasing the deflection due to a given radiation by a factor of 3. By a slight modification of the spectrometer, a thermopile having adjustable compensation can be utilized which, theoretically, will give almost no drifts due to changes in temperature of the optical parts of the spectrometer or of the surroundings.
A convenient technique of construction is described.