Fahrenheit
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rv. - removal was appropriate; uncited, plus "notable" feature is opinion (metirc users don't find the system awkward)
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'''Fahrenheit''' is a [[temperature|temperature scale]] named after [[Daniel Gabriel Fahrenheit]] (1686–1736), the [[Germany|German]] [[physicist]] who proposed it in 1724.
In this scale, the freezing point of [[water]] is 32 degrees Fahrenheit (°F) and the [[boiling point]] 212 °F, placing the boiling and freezing points of water exactly 180 degrees apart. A degree on the Fahrenheit scale is 1/180th part of interval between the ice point and steam point or boiling point. On the [[Celsius]] scale, the freezing and boiling points of water are exactly 100 degrees apart, thus the [[units of measurement|unit]] of this scale. A temperature interval of one degree Fahrenheit is an interval of {{frac|5|9}} of a degree Celsius. The Fahrenheit and Celsius scales coincide at −40 degrees (i.e. ''−40 °F'' and ''−40 °C'' describe the same temperature).
[[Absolute zero]] is −459.67 °F. The ''[[Rankine scale|Rankine]]'' temperature scale was created to use degrees the same size as those of the Fahrenheit scale, such that a temperature difference of one degree Rankine (1 °R) is the same as a temperature difference of 1 °F, but with absolute zero being 0 °R.
== History ==
According to Fahrenheit himself in an article he wrote in 1724,<ref name='ftempsc'> {{cite web|url=http://www.sizes.com/units/temperature_Fahrenheit.htm |title=Fahrenheit temperature scale |accessdate=2008-05-09 |date=2006-12-10 |publisher=Sizes, Inc }}</ref> he determined his scale by reference to three fixed points of temperature. The zero point is determined by placing the [[thermometer]] in a mixture of [[ice]], water, and [[ammonium chloride]], a salt. This is a type of [[frigorific mixture]]. The mixture automatically stabilizes its temperature at 0 °F. He then put an alcohol or mercury thermometer into the mixture and let the liquid in the thermometer descend to its lowest point. The second point is the 32nd degree found by putting the thermometer in still water as ice is just forming on the surface.<ref name='why32'> {{cite web|url=http://www.physlink.com/Education/AskExperts/ae64.cfm?CFID=21412834&CFTOKEN=55577927 |title=Why does the Fahrenheit scale use 32 degrees as a freezing point? |accessdate=2008-05-09 |last=Heath |first=Jonathan |publisher=PhysLink }}</ref> His third point, the 96th degree, was the level of the liquid in the thermometer when held in the mouth or under the armpit. Fahrenheit noted that, using this scale, mercury boils at around 600 degrees. Later work by other scientists observed that water boils about 180 degrees higher than the freezing point and decided to redefine the degree slightly to make it exactly 180<ref name='ftempsc'> {{cite web|url=http://www.sizes.com/units/temperature_Fahrenheit.htm |title=Fahrenheit temperature scale |accessdate=2008-05-09 |date=2006-12-10 |publisher=Sizes, Inc }}</ref> It is for this reason that normal body temperature is 98.6 on the revised scale (whereas it was 96 on Fahrenheit's original scale).<ref>{{Citation | last = Elert | first = Glenn | title = Temperature of a Healthy Human (Body Temperature) | url = http://hypertextbook.com/facts/LenaWong.shtml | accessdate = 04-12-2008}}.</ref>
According to a letter Fahrenheit wrote to his friend [[Herman Boerhaave]],<ref>Ernst Cohen and W. A. T. Cohen-De Meester. ''Chemisch Weekblad'', volume 33 (1936), pages 374–393, cited and translated in http://www.sizes.com:80/units/temperature_Fahrenheit.htm</ref> his scale built on the work of [[Ole Rømer]], whom he had met earlier. In [[Rømer scale|Rømer’s scale]], the two fixed reference points are that brine also freezes at 0 degrees and water boils at 60 degrees. He observed that, on this scale, water freezes at 7.5 degrees. Fahrenheit multiplied each value by four in order to eliminate the fractions and increase the granularity of the scale (resulting in 30 and 240 degrees). He then re-calibrated his scale between the freezing point of water and normal human body temperature (which he observed to be 96 degrees); he adjusted the scale so that the melting point of ice would be 32 degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power).<ref>{{cite web
|url=http://www.straightdope.com/classics/a4_188.html
|publisher=The Straight Dope
|title=On the Fahrenheit scale, do 0 and 100 have any special significance?
|author=Cecil Adams}}</ref>
== Usage ==
The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes in most English-speaking countries until the 1960s. In the late 1960s and 1970s, the [[Celsius]] (formerly ''Centigrade'') scale was phased in by governments as part of the standardizing process of [[metrication]].
Only in the [[United States]] and a few other countries (such as [[Belize]]<ref name='belizeweather'> {{cite web|url=http://www.hydromet.gov.bz/ |title=Belize Weather Bureau |accessdate=2008-05-09 }}</ref>) does the Fahrenheit system continue to be the accepted standard for non-scientific use. Most other countries have adopted Celsius as the primary scale in all use. Fahrenheit is sometimes used by older generations in English speaking countries, especially for measurement of higher temperatures and for cooking.{{Fact|date=March 2008}}
== The special Unicode “℉” character ==
The Fahrenheit symbol has its own [[Unicode]] character: “℉” (U+2109). This is a [[Unicode compatibility characters|compatibility character]] encoded for roundtrip compatibility with legacy [[CJK]] encodings (which included it to conform to layout in square [[ideographic]] character cells) and vertical layout. Use of compatibility characters is discouraged by the Unicode Consortium. The ordinary degree sign (U+00B0) followed by the Latin letter ''F'' (“°F”) is thus the preferred way of recording the symbol for ''degree Fahrenheit''.
==Temperatures and intervals==
As with the [[Celsius]] scale, the same symbol, "°", is used to denote both a point on the temperature scale, with a letter (C, F) indicating which scale is being used (e.g. “[[Gallium]] melts at 85.5763 °F”) and to denote a difference between temperatures or an uncertainty of temperature (e.g. “The output of the heat exchanger is hotter by 72 °C,” and “Our standard uncertainty is ±5.4 °C”).
== See also ==
* [[Comparison of temperature scales]]
== References ==
{{reflist}}
== External links ==
{{wiktionary}}
{{TemperatureScales}}
[[Category:Imperial units]]
[[Category:Units of temperature]]
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