Twenty-nine Gleams of Sunshine, August 7, 8, 9, in Nine Hours

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IN a paper, about weather, written by Mr. Ellis, of Greenwich Observatory, and published in NATURE, vol. xx. p. 313, mention is made of work done with an instrument for registering sunshine, which I contrived, got made, and gave to the Observatory. It consists of a glass sphere, a stand for it, and a metal bowl. The spherical surfaces have a common centre, and radii so measured that the focal cone of sunshine condensed by the glass is cut, by blackened cardboard fixed in the bowl, at the same distance, and at right angles, whatever the sun's position maybe in the visible sky. The temperature near the point is at least 700° when the weather is clear. The sun's circular image describes a circle about the common centre, and it burns a trace on cardboard when the sun shines clearly. I can think of nothing better or simpler for the purpose of registering sunshine and counting clouds daily.

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CAMPBELL, J. Twenty-nine Gleams of Sunshine, August 7, 8, 9, in Nine Hours. Nature 20, 403 (1879) doi:10.1038/020403b0

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