It was invented in 1853 by the Scottish Gaelic scholar Iain Òg Ìle, known in English as John Francis Campell. Perhaps unsurprisingly he was also the Secretary to the Lighthouse Commission at the time. It was adapted and improved in 1879 by Sir George Gabriel Stokes (pictured left) a Cambridge University based physicist and mathematician known for his work in fluid dynamics, mathematical physics and, importantly, optics. As president of the Royal Society and Commission he also investigated the causes of railway disasters during that period.
Campbell’s idea was straightforward but brilliant. A glass sphere would be placed in to a wooden bowl. The sun would burn a trace on the bowl as it the earth circled it - the above is a picture of the original now housed at the Science Museum in London. It worked and would measure the amount of sunshine in a single day with some accuracy. The downside, obviously, was the number of bowls which would have to be used to collect a significant amount of data – a year’s worth for example.
There are other versions of this simple device in use around the world. See pictures of them at Kuriositas. Link -via the Presurfer
(Image credit: Flickr user Science Museum London)