Weather in Space

The Sun

What is a Campbell-Stokes recorder?

A Campbell-Stokes recorder is a device for measuring not only the amount of sunlight reaching the ground, but also its intensity. Also called a Stokes sphere, it was invented in 1853 by John Francis Campbell (1821–1885), a Scotsman who was actually a Celtic scholar; his name is also cited as Iain Frangan Caimbeul an Iain Òg Ìle. Using a glass sphere to focus the Sun’s rays, Campbell placed a card with different marks on it to indicate times. Depending on the light’s intensity, the energy magnified by the glass burns the card. Differently marked cards are used depending on the season and whether one is in the Northern or Southern Hemisphere. The name Stokes comes from the English mathematician and physicist Sir George Gabriel Stokes (1819–1903), who improved the casing (he used metal) and changed the arrangement of the glass sphere and cards.


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