Heliothermometer (updated December 25 2023)

An insulated box with a thermometer inside, sunlight is allowed in through a window with three panes of clear glass, to measure sunlight, but not the outside air.    

Horace Bénédict de Saussure (1740-1799), a Swiss natural scientist, used Mariotte’s insight to design and build a “heliothermometer” to measure the relative intensity of sunlight. It was an insulated box with one side consisting of three layers of glass separated by air layers. 

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Image and conflicting information about altitude here

Not found on Wikipedia (Aug 7 2015)

Found in an IPCC report (archived)

Dec 25 2023, still not found on Wikipedia