Editing Nichols radiometer (section)

{{short description|Tool for measuring radiation pressure}}
[[File:Nichols radiometer.png|thumb|300px|right|Figures 1 and 2 in ''A Preliminary communication on the pressure of heat and light radiation'', Phys. Rev. 13, 307-320 (1901).]]
A '''Nichols radiometer''' was the apparatus used by [[Ernest Fox Nichols]] and [[Gordon Ferrie Hull]] in 1901 for the measurement of [[radiation pressure]]. 

It consisted of a pair of small silvered glass [[mirror]]s suspended in the manner of a [[torsion balance]] by a fine [[quartz]] fibre within an enclosure in which the air pressure could be regulated. The torsion head to which the fiber was attached could be turned from the outside using a [[magnet]]. A beam of [[light]] was directed first on one mirror and then on the other, and the opposite deflections observed with mirror and scale. By turning the mirror system around to receive the light on the unsilvered side, the influence of the air in the enclosure could be ascertained. This influence was found to be of almost negligible value at an air pressure of about {{cvt|16|mmHg|kPa atm psi}}. The [[radiant energy]] of the incident beam was deduced from its heating effect upon a small blackened silver disk, which was found to be more reliable than the [[bolometer]] when it was first used. With this apparatus, the experimenters were able to obtain an agreement between observed and computed radiation pressures within about 0.6%.

The original apparatus is at the [[Smithsonian Institution]].<ref>{{cite web|url=http://dujs.dartmouth.edu/spring-2008-10th-anniversary-edition/what-else-has-happened-a-celebration-of-the-legacy-of-physics-at-dartmouth|title=A Celebration of the Legacy of Physics at Dartmouth  |last=Lee|first=Dillon |year=2008|work=Dartmouth Undergraduate Journal of Science|publisher=Dartmouth College|access-date=2009-06-11}}</ref>

This apparatus is sometimes confused with the [[Crookes radiometer]] of 1873.

The original papers, with their historical context, have been re-printed in a chapter of the book ''Quantum Photonics: Pioneering Advances and Emerging Applications''.<ref>{{Citation |last=Garmire |first=Elsa |title=First Experiments on Measuring Light Pressure II (Ernest Fox Nichols and Gordon Ferrie Hull) |date=2019 |url=https://doi.org/10.1007/978-3-319-98402-5_13 |work=Quantum Photonics: Pioneering Advances and Emerging Applications |pages=455–479 |editor-last=Boyd |editor-first=Robert W. |access-date=2023-08-22 |series=Springer Series in Optical Sciences |volume=217 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-98402-5_13 |isbn=978-3-319-98402-5 |s2cid=171448261 |editor2-last=Lukishova |editor2-first=Svetlana G. |editor3-last=Zadkov |editor3-first=Victor N.|url-access=subscription }}</ref>