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 which 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.
Small - H: 12,5cm Ø: 6cm
Large - H: 17cm Ø: 9,5cm
Tall - H: 21cm Ø: 8cm