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# Crookes incorrectly suggested that the force was due to the pressure of light.

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# Another incorrect theory was that the heat on the dark side was causing the material to outgas, which pushed the radiometer around.

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# REDIRECTCrookes radiometer

# Scanning multichannel microwave radiometer to measure sea surface temperature

# Visible and infrared radiometer to identify cloud, land and water features

Crookes radiometer

The Crookes radiometer, also known as the light mill, consists of an airtight glass bulb, containing a partial vacuum.

A Crookes radiometer in action

A Crookes radiometer, consistent with the word-element " meter " in its title, can provide a quantitative measurement of electromagnetic radiation intensity.

When a radiant energy source is directed at a Crookes radiometer, the radiometer becomes a heat engine.

Over the years, there have been many attempts to explain how a Crookes radiometer works:

The first experiment to disprove this theory was done by Arthur Schuster in 1876, who observed that there was a force on the glass bulb of the Crookes radiometer that was in the opposite direction to the rotation of the vanes.

The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate.

Both Einstein's and Reynolds's forces appear to cause a Crookes radiometer to rotate, although it still isn't clear which one is stronger.

In 2010 researchers at the University of California, Berkeley succeeded in building a nanoscale light mill that works on an entirely different principle to the Crookes radiometer.

da: Crookes ' radiometer

He was the inventor of the Crookes radiometer, which today is made and sold as a novelty item.

He soon discovered the phenomenon upon which depends the action of the Crookes radiometer, in which a system of vanes, each blackened on one side and polished on the other, is set in rotation when exposed to radiant energy.

The pressure is very feeble, but can be detected by allowing the radiation to fall upon a delicately poised vane of reflective metal in a Nichols radiometer ( this should not be confused with the Crookes radiometer, whose characteristic motion is not caused by radiation pressure but by impacting gas molecules ).

This apparatus is sometimes confused with the Crookes radiometer of 1873, in which vanes turn in a partial vacuum under the influence of low pressure gas molecules and not directly by the photons themselves.

Ernest Fox Nichols used a modified Crookes radiometer in an attempt to detect infrared radiation from Arcturus and Vega, but Nichols deemed the results inconclusive.

In other departments of physics may be mentioned his paper on the conduction of heat in crystals ( 1851 ) and his inquiries in connection with Crookes radiometer ; his explanation of the light border frequently noticed in photographs just outside the outline of a dark body seen against the sky ( 1883 ); and, still later, his theory of the x-rays, which he suggested might be transverse waves travelling as innumerable solitary waves, not in regular trains.

Two years later, researches on " Charcoal Vacua " with James Dewar led him to see the true dynamical explanation of the Crookes radiometer in the large mean free path of the molecule of the highly rarefied air.

* Crookes radiometer

An example of a Crookes radiometer.

A common example is the Crookes radiometer, an early-model device wherein a rotor ( having vanes which are dark on one side, and light on the other ) in a partial vacuum spins when exposed to light.

A common myth ( one originally held even by Crookes ) is that the momentum of the absorbed light on the black faces makes the radiometer operate.