Invented in 1873 by chemist & experimenter Sir William Crookes, the solar radiometer was the first way in which 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. When exposed to sunlight, artificial light, or infrared radiation, the vanes turn with no apparent motive power, the dark sides retreating from the radiation source and the light sides advancing...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.