This is the Campbell-Stokes sun recorder used by meteorologists to record the amount of sunshine in a given day. It is the most widely-used sunshine recorder in the world and remains largely unchanged since it was first invented by scholar James Francis Campbell in 1853 and later refined in 1879 by physicist George Gabriel Stokes. Intended to be left outside all year, the recorders 4" diam. annealed optical glass sphere focuses the suns rays into a fine point onto a paper card inserted into the bowls grooves, marking a line to indicate the hours of sunshine. The sphere attaches to a solid brass arc inscribed with degrees in latitude and the arc rests upon a base cast from non-corrosive gunmetal; screw holes allow you to attach it to the included wooden platform for indoor display or a post for outdoor use. Includes a years-worth of three types of cards to correspond to the behavior of the sun at different seasons (summer, winter, and equinoctial). 9 1/2" H x 7 1/2" W x 6 1/2" D. (9 1/2 lbs.)