Antique sunshine autograph, heliograph, sunshine measuring instrument made around 1900. Inspired by Campbell Stokes. The sunshine autograph was used to measure the sunshine duration of a day. This is how it works: A big glass ball is used as a burning lens, behind the glass, where the light is bundled, is placed a plastic or paper stripe with a time marker. When the sun shines, the light burns marks into the paper. So one can see at what time and how long the sun was shining and by adding those marks, the duration of sunshine can be calculated. Interesting collector´s piece!