Maker's Name: 
Where made: 
7.5 × 7.5 × 12 cm

The bulb is evacuated to a soft vacuum. The rotating vanes pivot on the point of a wire. They are silvered one side and blackened the other. Radiation received by the blackened side heats that side and the adjacent gas molecules, creating convection currents in the gas. The reaction causes the vanes to rotate, the silvered sides leading the blackened sides.

Note that the vanes are NOT driven by radiation reflected by the silvered side, with the blackened side absorbing the radiation. Were it so, the blackened sides would lead the silvered sides. Also the momentum of the radiation source is not strong enough to cause rotation.