The Crookes Radiometer or 'Light Mill' is a fascinating physics toy. The glass bulb contains a near vacuum, and 4 mica crystal vanes that rotate with very low friction. Place the Radiometer in sunlight and the vanes will spin happily around, just driven by the light!The Radiometer will also work with most warm artificial lights.
Invented by the British scientist Sir William Crookes in 1873, people initially thought it showed 'radiaion pressure'. In fact it is a kind of heat engine.
24cm high, these Radiometers are hand made in Germany. There is a metal oxide in the base, which gives the rich red colour. The vanes are made of mica.
For an explanation of how they work, see http://en.wikipedia.org/wiki/Crookes_radiometer