Variation of Diathermancy with the Temperature of the Radiating Source

Instrument for measuring radiant heat energy.—The radiation is focused by a mirror on a thin piece of copper oxide, 1 ${\mathrm{mm}.\mathrm{}}^2$ in area, with a resistance of 10,000 ohms and a temperature coefficient of resistance of 0.01 per degree. Such an instrument is simple to construct and use and is easily made sensitive to one per cent. of the radiation from a tubular electric furnace at 500° C.