A thermopile consisting of 50 couples is made from 6Au-40Pd with 90Pt-10Rh wire 0.0016 inch in diameter, by electrically fusing the junctions. Alternate junctions are attached to, but electrically insulated from, two thin concentric copper rings. The inner ring has its upper surface painted black; the outer ring, white. Details of construction are given.
When exposed to solar radiation, the excess in temperature of the junctions attached to the blackened ring over those attached to the whitened ring produces an electric current, the voltage of which is very nearly proportional to the intensity of the solar radiation. With a solar radiation intensity of one gram-calory per minute per square centimeter of surface the current generated has a voltage of between 9 and 10 millivolts.
A Type RM Engelhard recording voltmeter is employed to obtain continuous records of the solar radiation intensity. A sample record and illustrations of the thermopile are given.
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