A glass light mill based on “Crookes radiometer” by Hightide. This is the small size. 

A radiometer is a device that has been used since the 1800s to measure the power of electromagnetic radiation. Ours take the form of the original "light mill” invented by William Crookes in 1873, in which the rotor spins in different speeds depending on the intensity of the radiant energy.

* Please not that the our radiometer vanes (wings) spin under sunlight.

Dimension: (Φ)2.4" x (H)5.5"

Also available in Large