The FAHRENHEIT SCALE is a temperature scale based on one proposed in
1724 by Amsterdam-based physicist
Daniel Gabriel Fahrenheit
By the end of the 20th century,
Fahrenheit was used as the official
temperature scale only in the
United States (including its
unincorporated territories ), its freely associated states in the
Western Pacific (
* 1 Definition and conversion * 2 History * 3 Usage * 4 Unicode representation of symbol * 5 See also * 6 Notes and references * 7 External links
DEFINITION AND CONVERSION
FAHRENHEIT TEMPERATURE CONVERSION FORMULAE
FROM FAHRENHEIT TO FAHRENHEIT
CELSIUS = ( − 32) × 5⁄9 = × 9⁄5 + 32
KELVIN = ( + 459.67) × 5⁄9 = × 9⁄5 − 459.67
RANKINE = + 459.67 = − 459.67
For temperature intervals rather than specific temperatures, 1 °F = 1 °R = 5⁄9 °C = 5⁄9 K Comparisons among various temperature scales
On the Fahrenheit scale, the freezing point of water is 32 degrees Fahrenheit (°F) and the boiling point is 212 °F (at standard atmospheric pressure ). This puts the boiling and freezing points of water exactly 180 degrees apart. Therefore, a degree on the Fahrenheit scale is 1⁄180 of the interval between the freezing point and the boiling point. On the Celsius scale, the freezing and boiling points of water are 100 degrees apart. A temperature interval of 1 °F is equal to an interval of 5⁄9 degrees Celsius. The Fahrenheit and Celsius scales intersect at −40° (i.e., −40 °F = −40 °C).
Absolute zero is −273.15 °C or −459.67 °F. The Rankine
temperature scale uses degree intervals of the same size as those of
Fahrenheit scale, except that absolute zero is 0 °R — the same
way that the
Fahrenheit scale uses the symbol ° to denote a point on the
temperature scale (as does Celsius) and the letter F to indicate the
use of the
Fahrenheit scale (e.g. "
For an exact conversion, the following formulas can be applied. Here, f is the value in Fahrenheit and c the value in Celsius:
This is also an exact conversion making use of the identity -40 °F = -40 °C. Again, f is the value in Fahrenheit and c the value in Celsius:
Daniel Gabriel Fahrenheit
Fahrenheit proposed his temperature scale in 1724, basing it on two reference points of temperature. In his initial scale (which is not the final Fahrenheit scale), the zero point was determined by placing the thermometer in a mixture of ice , water, and ammonium chloride (salis Armoniaci). This is a frigorific mixture which stabilizes its temperature automatically: that stable temperature was defined as 0 °F (−17.78 °C). The second point, 96 degrees, was approximately the human body's temperature (sanguine hominis sani, the blood of a healthy man).
According to a story in Germany, Fahrenheit actually chose the lowest air temperature measured in his hometown Danzig in winter 1708/09 as 0 °F, and only later had the need to be able to make this value reproducible using brine. This is one explanation given why 0 °F is −17.78 °C, but the ammonium chloride cooling temperature actually is −3 °C, whereas that of NaCl is −21.1 °C; the other explanation is that he did not have a good enough brine solution to obtain the eutectic equilibrium exactly (i.e. he might have had a mixture of salts, or it had not fully dissolved). In any case, the definition of the Fahrenheit scale has changed since.
According to a letter
Fahrenheit wrote to his friend Herman Boerhaave
, his scale was built on the work of
Fahrenheit observed that water boils at about 212 degrees using this
scale. The use of the freezing and boiling points of water as
thermometer fixed reference points became popular following the work
Celsius and these fixed points were adopted by a committee
The Rankine temperature scale was based upon the Fahrenheit temperature scale, with its zero representing absolute zero instead.
Countries that use Fahrenheit. Countries that use Celsius.
The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes in English-speaking countries until the 1960s. In the late 1960s and 1970s, the Celsius scale replaced Fahrenheit in almost all of those countries—with the notable exception of the United States—typically during their metrication process.
Fahrenheit is used in the United States, its territories and
associated states (all served by the U.S.
National Weather Service ),
as well as the
Early in the twentieth century, Halsey and Dale suggested that the resistance to the use of centigrade (now Celsius) system in the U.S. included the larger size of each degree Celsius and the lower zero point in the Fahrenheit system.
Canada has passed legislation favoring the International System of Units , while also maintaining legal definitions for traditional Canadian imperial units. Canadian weather reports are conveyed using degrees Celsius with occasional reference to Fahrenheit especially for cross-border broadcasts. Virtually all Canadian ovens make legal use of the Fahrenheit scale. Thermometers, both digital and analog, sold in Canada usually employ both the Celsius and Fahrenheit scales. Also, in some instances (swimming pool temperature or cooking temperatures for example), temperatures are still expressed in Fahrenheit. European laundry symbol for "Wash at 40 °C"
Within the European Union, it is mandatory to use kelvins or degrees Celsius when quoting temperature for "economic, public health, public safety and administrative" purposes, though degrees Fahrenheit may be used alongside degrees Celsius as a supplementary unit. For example, the laundry symbols used in the United Kingdom follow the recommendations of ISO 3758:2005 showing the temperature of the washing machine water in degrees Celsius only. The equivalent label in North America uses one to six dots to denote temperature with an optional temperature in degrees Celsius.
Within the unregulated sector, such as journalism, the use of
Fahrenheit in the United Kingdom follows no fixed pattern with degrees
Fahrenheit often appearing alongside degrees Celsius. The
Daily Mail ,
on its daily weather page, quotes
Celsius first, followed by
Fahrenheit in brackets,
The Daily Telegraph
UNICODE REPRESENTATION OF SYMBOL
Unicode provides the Fahrenheit symbol at codepoint U+2109 ℉ degree fahrenheit. However, this is a compatibility character encoded for roundtrip compatibility with legacy encodings. The Unicode standard explicitly discourages the use of this character: "The sequence U+00B0 ° degree sign +U+0046 F latin capital letter f is preferred over U+2109 ℉ degree fahrenheit, and those two sequences should be treated as identical for searching."
* Energy portal
NOTES AND REFERENCES
* ^ Robert T. Balmer (2010). Modern Engineering Thermodynamics. Academic Press. p. 9. ISBN 978-0-12-374996-3 . Retrieved 17 July 2011.
* ^ Fahrenheit temperature scale, Encyclopædia Britannica Onlinbe. 25 September 2015 * ^ * ^ Celsius vs. Fahrenheit * ^ A B Walt Boyes (2009). Instrumentation Reference Book. Butterworth-Heinemann. pp. 273–274. ISBN 978-0-7506-8308-1 . Retrieved 17 July 2011. * ^ Preston–Thomas, H. (1990). "The International Temperature Scale of 1990 (ITS-90)" (PDF). Metrologia. 27: 6. Bibcode :1990Metro..27....3P. doi :10.1088/0026-1394/27/1/002 . Retrieved 17 July 2011.
* ^ "Sal Armoniac" was an impure form of ammonium chloride. The French chemist Nicolas Lémery (1645 – 1715) discussed it in his book Cours de Chymie (A Course of Chemistry, 1675), describing where it occurs naturally and how it can be prepared artificially. It occurs naturally in the deserts of northern Africa, where it forms from puddles of animal urine. It can be prepared artificially by boiling 5 parts of urine, 1 part of sea salt, and ½ part of chimney soot until the mixture has dried. The mixture is then heated in a sublimation pot until it sublimates ; the sublimated crystals are sal Armoniac. See:
* Nicolas Lémery, Cours de chymie … , 7th ed. (Paris, France: Estienne Michallet, 1688), Chapitre XVII: du Sel Armoniac, pp. 338-339. * English translation: Nicolas Lémery with James Keill, trans., A Course of Chymistry … , 3rd ed. (London, England: Walter Kettilby, 1698), Chap. XVII: of Sal Armoniack, p. 383. Available on-line at: Heinrich Heine University (Düsseldorf, Germany)
* ^ Fahrenheit, Daniele Gabr. (1724) "Experimenta circa gradum
caloris liquorum nonnullorum ebullientium instituta" (Experiments
performed concerning the degree of heat of some boiling liquids),
Philosophical Transactions of the
Look up FAHRENHEIT in Wiktionary, the free dictionary.
Daniel Gabriel Fahrenheit
* "At Auction