Inventor : Sir. William Crookes
What is it?
Device to measure electromagnetic radiation.
What is it made of?
An airtight partial vacuum glass bulb with set of vanes mounted on a spindle through a frictionless rotor inside.
The vanes are equally spaced. One side of vane is black and the other side white.
How does it work?
When electromagnetic radiation is incident on the device, the region near white side of vane gets warmer than the black side of vane.
As white side reflects radiation, it warms the air molecules more than the black side which absorbs radiation.
These gas molecules move from cooler region to warmer region thus pushing the vane from white side to black side.
This phenomenon is called thermal transpiration.
Facts
It is also known as light mill.
It was an accidental invention.
The correct phenomenon of it’s working was discovered later.
Where can I get one?
Benny's science blog 