Editing Daniel Gabriel Fahrenheit (section)

== Fahrenheit scale ==
{{main|Fahrenheit}}
According to Fahrenheit's 1724 article,<ref name="ftempsc"/><ref>Fahrenheit describes, in Latin, these numerical choices in the following paper: {{cite journal |author=Fahrenheit, D. G. |title=Experimenta et Observationes de Congelatione aquae in vacuo factae |journal=Philosophical Transactions of the Royal Society |volume=33 |pages=78–84 |year=1724 |doi=10.1098/rstl.1724.0016 |issue=381–391 |doi-access=free }}</ref> he determined his scale by reference to three fixed points of [[temperature]].  The lowest temperature was achieved by preparing a [[frigorific mixture]] of [[ice]], water, and a salt ("[[ammonium chloride]] or even sea salt"), and waiting for the [[eutectic system]] to reach [[equilibrium temperature]].  The thermometer then was placed into the mixture and the liquid in the thermometer allowed to descend to its lowest point.  The thermometer's reading there was taken as {{not a typo|0&nbsp;°F}}.  The second reference point was selected as the reading of the thermometer when it was placed in still water when ice was 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? |access-date=9 May 2008 |last=Heath |first=Jonathan |publisher=PhysLink}}</ref> This was assigned as {{not a typo|30&nbsp;°F}}. The third calibration point, taken as {{not a typo|90&nbsp;°F}}, was selected as the thermometer's reading when the instrument was placed under the arm or in the mouth.<ref name="Burdge2014">{{cite book|last=Burdge|first=Julia|title=Chemistry: Atoms First|url=https://books.google.com/books?id=2XVzCgAAQBAJ&pg=PA11|access-date=16 September 2017|date=10 January 2014|publisher=McGraw-Hill|isbn=9780077646479|page=11}}</ref>

Fahrenheit came up with the idea that mercury boils around 300 degrees on this [[temperature scale]]. Work by others showed that water boils about 180 degrees above its freezing point.  The Fahrenheit scale later was redefined to make the freezing-to-boiling interval exactly 180 degrees,<ref name="ftempsc">{{cite web|url=http://www.sizes.com/units/temperature_Fahrenheit.htm |title=Fahrenheit temperature scale |access-date=9 May 2008 |date=10 December 2006 |publisher=Sizes, Inc}}</ref> a convenient value as 180 is a [[highly composite number]], meaning that it is evenly divisible into many fractions. It is because of the scale's redefinition that normal mean body temperature today is taken as 98.6 degrees,<ref>{{cite journal |doi=10.1001/jama.1992.03490120092034 |title=A Critical Appraisal of 98.6°F, the Upper Limit of the Normal Body Temperature, and Other Legacies of Carl Reinhold August Wunderlich |year=1992 |last1=MacKowiak |first1=Philip A. |journal=JAMA: The Journal of the American Medical Association |volume=268 |issue=12 |pages=1578–80 |pmid=1302471}}</ref> whereas it was 96 degrees on Fahrenheit's original scale.<ref>{{cite journal |last1=Elert |first1=Glenn |title=Temperature of a Healthy Human (Body Temperature) |url=http://hypertextbook.com/facts/1997/LenaWong.shtml |access-date=4 December 2008 |doi=10.1046/j.1471-6712.2002.00069.x |year=2002 |journal=Scandinavian Journal of Caring Sciences |volume=16 |pages=122–8 |pmid=12000664 |last2=Forsberg |first2=C |last3=Wahren |first3=LK |issue=2}}</ref>

The [[Fahrenheit|Fahrenheit scale]] was the primary temperature standard for climatic, industrial and medical purposes in English-speaking countries until the 1970s, presently mostly replaced by the [[Celsius|Celsius scale]] long used in the rest of the world, apart from the United States, where temperatures and weather reports are still broadcast in Fahrenheit.<ref>{{cite web |url= https://www.livescience.com/39916-fahrenheit.html |title= Fahrenheit: Facts, History & Conversion Formulas |first= Kim Ann |last= Zimmermann |website= [[Live Science]] |date= 24 September 2013 |access-date= 16 September 2017}}</ref>