Day 120
April 30, 2010I spotted this in the grounds of Chatsworth House which is close by where we live.
It’s a Campbell-Stokes recorder (sometimes called aStokes sphere) is a kind of sunshine recorder.
It was invented by John Francis Campbell in 1853 and later modified in 1879 by Sir George Gabriel Stokes. The original design by Campbell consisted of a glass sphere set into a wooden bowl with the sun burning a trace on the bowl. Stokes’s refinement was to make the housing out of metal and to have a card holder set behind the sphere.This basic unit is still in use today with very little change.
The unit is designed to record the hours of bright sunshine which will burn a hole through the card. However, at sunrise and sunset the sun is lower in the sky and will tend to leave a scorch mark on the card which may at the extreme end be difficult to see.
The glass sphere – typically 10 cm (4 inches) in diameter – is designed to focus the rays from the sun onto a card mounted at the back and is set on a stand. The card is held in place by grooves of which there are three overlapping sets, to allow for the height of the sun during different seasons of the year.