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.

Diathermancy of various substances to the total radiation from a tubular furnace for temperatures from 200 to 1,200° C.—For furnace temperatures of 400, 700 and 1,000° the percentages transmitted are as follows: water (½ mm.), 4.6, 14.4, 24.8; ice (3 mm.), —, 4.6, 15; rock salt (11 mm. clear), 85.6, 87, 89; white mica (1 mm.), 6, 14, 29; glass (1.2 mm.), 10.6, 22, 40. A column of moist air 2.5 meters long containing 0.032 mm. of precipitable water absorbed 8.7 and 7.1 per cent. for temperatures of 510 and 850° respectively.

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