COUNTRY SCIENTIST

Ultra-Simple Sunshine Recorders

BY FORREST M. MIMS III

SUNSHINE IS ESSENTIAL FOR PLANT growth, which is one reason scientists have developed so many methods to measure it.

In a future column I’ll show how to measure sunshine electronically. But first, let’s enter the MAKE time machine and zip back to 1838, when instrument maker T.B. Jordan made the first known automatic sunshine recorder.

Jordan wrapped a strip of silver chloride photographic paper around a clock-driven cylinder, and mounted it behind the mercury column of a barometer. The photo paper was exposed to sunlight as it rotated past an aperture, and this provided a record of when clouds blocked the sun. The width of the exposed portion of the paper was controlled ...

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