Invented in 1873 by chemist & experimenter Sir William Crookes, the solar radiometer was the first way a man could demonstrate light as an energy source.
The radiometer consists of an airtight glass bulb containing a partial vacuum. Inside are a set of metal vanes that are mounted on a spindle. The vanes turn with no apparent motive power when exposed to sunlight, artificial light, or infrared radiation. The dark sides retreat from the radiation source, and the light sides advance...the more intense the light, the faster the rotation.
The glass globe rests securely on a handsome wood base. 4.25 x 3.25" in diameter.