Daily Almanac for

Dec 11, 2009

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Radiometer

The name of an instrument invented by Crookes for measuring the mechanical effect of radiant energy. It is like a miniature anemometer, and is made to revolve by the action of light, the cups of the anemometer being replaced by discs coloured white on one side and black on the other, and the instrument is enclosed in a glass globe from which the air has been exhausted, so that no heat is transmitted.

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