Radiometer (large)

The radiometer is also known as a light mill, solar power station or the Crookes radiometer.  It was invented by the chemist and physicist Sir William Crookes.  Heat rays from the sun or a light bulb warm up the dark side of the rotating blade – and therefore the air close to it –  more than the light side. The difference in air pressure causes the blade to turn.

Height: about 17 cm
Diameter: about 7 cm