This is a simplified version of the original sunshine recorder designed by T. B. Jordan and adopted by Negretti & Zambra as a more economical way of recording the hours of sunshine. The traditional and more expensive Campbell Stokes recorder uses a glass sphere to focus the sun's rays on to a printed card. This Jordan recorder uses a light-tight cylinder with a pin hole allowing the suns rays to leave a trace on sensitised chart, similar to paper used in blueprint drawings and still available today. Often bought for schools and those with limited budget, this fine instrument can still be used and would also make a lovely stand-alone collectors item.  An extract from Negretti & Zambra's 1950 trade catalogue describes the function in more detail.
Base 115mm x 115mm. Height approx. 180mm