These new and mesmerising instruments from Nauticalia will measure the power of electromagnetic radiation.
The glass bulb has had much of the air removed, thus forming a partial vacuum. Inside is a set of fine metal vanes, each with one dark and one light side - mounted on a spindle. As the vanes rotate, when they are exposed to sunlight, artificial light or infrared radiation the more intense the light and faster the rotation.
They are pretty magical to watch.
Dimensions: 185mm x 60mm