Campbell-Stokes recorder: How to measure sunlight

The Campbell-Stokes recorder is a device for measuring sunshine duration. It consists of a glass sphere that acts as a lens and concentrates the sun's rays onto a special paper tape located in a metal arc-shaped frame.

When the sun shines brightly enough, the concentrated light burns through the tape, leaving marks on it. The length of these marks can be used to determine the number of hours of sunshine per day. Different scales on the tape are used for different seasons, since the angle of incidence of the sun's rays changes. This device is widely used in meteorology and climatology to study solar activity and its impact on the environment.