Last updated

Raumthermometer Fahrenheit+Celsius.jpg
Thermometer with Fahrenheit (marked on outer bezel) and Celsius (marked on inner dial) degree units. The Fahrenheit scale was the first standardized temperature scale to be widely used.
General information
Unit system Imperial/US customary
Unit ofTemperature
Named after Daniel Gabriel Fahrenheit
x °F in ...... is equal to ...
    °C    (x − 32) × 0.55 °C

The Fahrenheit scale is a temperature scale based on one proposed in 1724 by Dutch–German–Polish physicist Daniel Gabriel Fahrenheit (1686–1736). [1] It uses the degree Fahrenheit (symbol: °F) as the unit. Several accounts of how he originally defined his scale exist. The lower defining point, 0 °F, was established as the freezing temperature of a solution of brine made from equal parts of ice, water and salt (ammonium chloride). [2] Further limits were established as the melting point of ice (32 °F) and his best estimate of the average human body temperature (96 °F, about 2.6 °F less than the modern value due to a later redefinition of the scale). [3] The scale is now usually defined by two fixed points: the temperature at which water freezes into ice is defined as 32 °F, and the boiling point of water is defined to be 212 °F, a 180 °F separation, as defined at sea level and standard atmospheric pressure.

Scale of temperature is a way to measure temperature quantitatively. Empirical scales measure the quantity of heat in a system in relation to a fixed parameter, a thermometer. They are not absolute measures, that is why scales vary. Absolute temperature is thermodynamic temperature because it is directly related to thermodynamics. It is the Zeroth Law of Thermodynamics that leads to a formal definition of thermodynamic temperature.

Physicist scientist who does research in physics

A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate causes of phenomena, and usually frame their understanding in mathematical terms. Physicists work across a wide range of research fields, spanning all length scales: from sub-atomic and particle physics, through biological physics, to cosmological length scales encompassing the universe as a whole. The field generally includes two types of physicists: experimental physicists who specialize in the observation of physical phenomena and the analysis of experiments, and theoretical physicists who specialize in mathematical modeling of physical systems to rationalize, explain and predict natural phenomena. Physicists can apply their knowledge towards solving practical problems or to developing new technologies.

Daniel Gabriel Fahrenheit German-Polish physicist and engineer

Daniel Gabriel Fahrenheit FRS was a German physicist, inventor, and scientific instrument maker. Fahrenheit was born in Danzig/Gdańsk, a predominantly German-speaking Hanseatic city in the Pomeranian Voivodeship of the Polish–Lithuanian Commonwealth, but lived most of his life in the Dutch Republic (1701–1736) and was one of the notable figures in the Golden Age of Dutch science and technology.


At the end of the 2010s, 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 (Palau, the Federated States of Micronesia and the Marshall Islands), the Bahamas, the Cayman Islands and Liberia. Antigua and Barbuda and other islands which use the same meteorological service, such as Anguilla, the British Virgin Islands, Montserrat and Saint Kitts and Nevis, as well as Bermuda, Belize and the Turks and Caicos Islands, use Fahrenheit and Celsius. All other countries in the world officially now use the Celsius scale, named after Swedish astronomer Anders Celsius.

United States Federal republic in North America

The United States of America (USA), commonly known as the United States or America, is a country comprising 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico. The State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The extremely diverse geography, climate, and wildlife of the United States make it one of the world's 17 megadiverse countries.

Under United States law, an unincorporated territory is an area controlled by the United States government that is not "incorporated" for the purposes of United States constitutional law. In unincorporated territories, the U.S. Constitution applies only partially. In the absence of an organic law, a territory is classified as unorganized. In unincorporated territories, "fundamental rights apply as a matter of law, but other constitutional rights are not available". Selected constitutional provisions apply, depending on congressional acts and judicial rulings according to U.S. constitutional practice, local tradition, and law.

The Compact of Free Association (COFA) is an international agreement establishing and governing the relationships of free association between the United States and the three Pacific Island nations of the Federated States of Micronesia, the Marshall Islands, and Palau. These nations, together with the Commonwealth of the Northern Mariana Islands, formerly composed the Trust Territory of the Pacific Islands, a United Nations trusteeship administered by the United States Navy from 1947 to 1951 and by the U.S. Department of the Interior from 1951 to 1986.

Definition and conversion

Fahrenheit temperature conversion formulae
from Fahrenheitto Fahrenheit
Celsius [°C] = ([°F]  32) × 59[°F] = [°C] × 95 + 32
Kelvin [K] = ([°F] + 459.67) × 59[°F] = [K] × 95  459.67
Rankine [°R] = [°F] + 459.67[°F] = [°R]  459.67
For temperature intervals rather than specific temperatures,
1 °F = 1 °R = 59 °C = 59 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 180 degrees apart. [4] Therefore, a degree on the Fahrenheit scale is 1180 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 59 degrees Celsius. The Fahrenheit and Celsius scales intersect at −40° (i.e., −40 °F = −40 °C).

Water chemical compound

Water is a transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's streams, lakes, and oceans, and the fluids of most living organisms. It is vital for all known forms of life, even though it provides no calories or organic nutrients. Its chemical formula is H2O, meaning that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. Water is the name of the liquid state of H2O at standard ambient temperature and pressure. It forms precipitation in the form of rain and aerosols in the form of fog. Clouds are formed from suspended droplets of water and ice, its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or water vapor. Water moves continually through the water cycle of evaporation, transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea.

Boiling point temperature

The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.

Absolute zero is −273.15 °C or −459.67 °F. The Rankine temperature scale uses degree intervals of the same size as those of the Fahrenheit scale, except that absolute zero is 0 °R — the same way that the Kelvin temperature scale matches the Celsius scale, except that absolute zero is 0 K. [4]

Absolute zero coldest possible temperature

Absolute zero is the lowest limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as 0. The fundamental particles of nature have minimum vibrational motion, retaining only quantum mechanical, zero-point energy-induced particle motion. The theoretical temperature is determined by extrapolating the ideal gas law; by international agreement, absolute zero is taken as −273.15° on the Celsius scale, which equals −459.67° on the Fahrenheit scale. The corresponding Kelvin and Rankine temperature scales set their zero points at absolute zero by definition.

The Kelvin scale is an absolute thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. The kelvin is the base unit of temperature in the International System of Units (SI).

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. "Gallium melts at 85.5763 °F"), [5] as well as to denote a difference between temperatures or an uncertainty in temperature (e.g. "The output of the heat exchanger experiences an increase of 72 °F" and "Our standard uncertainty is ±5 °F").

The degree symbol (°) is a typographical symbol that is used, among other things, to represent degrees of arc, hours, degrees of temperature, alcohol proof, or diminished quality in musical harmony. The symbol consists of a small raised circle, historically a zero glyph.

Gallium Chemical element with atomic number 31

Gallium is a chemical element with the symbol Ga and atomic number 31. Elemental gallium is a soft, silvery blue metal at standard temperature and pressure; however in its liquid state it becomes silvery white. If too much force is applied, the gallium may fracture conchoidally. It is in group 13 of the periodic table, and thus has similarities to the other metals of the group, aluminium, indium, and thallium. Gallium does not occur as a free element in nature, but as gallium(III) compounds in trace amounts in zinc ores and in bauxite. Elemental gallium is a liquid at temperatures greater than 29.76 °C (85.57 °F), above room temperature, but below the normal human body temperature of 37 °C (99 °F). Hence, the metal will melt in a person's hands.

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, a pioneer of exact thermometry (temperature measurement). He invented the mercury thermometer (first practical, accurate thermometer) and Fahrenheit scale (first widely used, standardized temperature scale). Fahrenheit small.jpg
Daniel Gabriel Fahrenheit, a pioneer of exact thermometry (temperature measurement). He invented the mercury thermometer (first practical, accurate thermometer) and Fahrenheit scale (first widely used, standardized temperature scale).

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, of water, and of ammonium chloride (salis Armoniaci) [6] or even of sea salt". This combination forms a eutectic system which stabilizes its temperature automatically: 0 °F was defined to be that stable temperature. The second point, 96 degrees, was approximately the human body's temperature (sanguine hominis sani, the blood of a healthy man). [7]

Thermometer Device to measure temperature

A thermometer is a device that measures temperature or a temperature gradient. A thermometer has two important elements: (1) a temperature sensor in which some change occurs with a change in temperature; and (2) some means of converting this change into a numerical value. Thermometers are widely used in technology and industry to monitor processes, in meteorology, in medicine, and in scientific research.

Ice water frozen into the solid state

Ice is water frozen into a solid state. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color.

Ammonium chloride chemical compound

Ammonium chloride is an inorganic compound with the formula NH4Cl and a white crystalline salt that is highly soluble in water. Solutions of ammonium chloride are mildly acidic. Sal ammoniac is a name of the natural, mineralogical form of ammonium chloride. The mineral is commonly formed on burning coal dumps from condensation of coal-derived gases. It is also found around some types of volcanic vents. It is mainly used as fertilizer and a flavouring agent in some types of liquorice. It is the product from the reaction of hydrochloric acid and ammonia.

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. [8]

According to a letter Fahrenheit wrote to his friend Herman Boerhaave, [9] his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer's scale, brine freezes at zero, water freezes and melts at 7.5 degrees, body temperature is 22.5, and water boils at 60 degrees. Fahrenheit multiplied each value by four in order to eliminate fractions and make the scale more fine-grained. He then re-calibrated his scale using the melting point of ice and normal human body temperature (which were at 30 and 90 degrees); he adjusted the scale so that the melting point of ice would be 32 degrees and body temperature 96 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). [10] [11]

Fahrenheit soon after observed that water boils at about 212 degrees using this scale. [12] The use of the freezing and boiling points of water as thermometer fixed reference points became popular following the work of Anders Celsius and these fixed points were adopted by a committee of the Royal Society led by Henry Cavendish in 1776. [13] Under this system, the Fahrenheit scale is redefined slightly so that the freezing point of water is exactly 32 °F, and the boiling point is exactly 212 °F or 180 degrees higher. It is for this reason that normal human body temperature is approximately 98° (oral temperature) on the revised scale (whereas it was 90° on Fahrenheit's multiplication of Rømer, and 96° on his original scale). [14]

In the present-day Fahrenheit scale, 0 °F no longer corresponds to the eutectic temperature of ammonium chloride brine as described above. Instead, that eutectic is at approximately 4 °F on the final Fahrenheit scale. [15]

The Rankine temperature scale was based upon the Fahrenheit temperature scale, with its zero representing absolute zero instead.


Countries that use Fahrenheit (degF).
Countries that use Celsius (degC). Countries that use Fahrenheit.svg
  Countries that use Fahrenheit (°F).
  Countries that use Celsius (°C).
Thermometer CF.svg

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 general 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 Bahamas, the Cayman Islands and Liberia for everyday applications. For example, U.S. weather forecasts, food cooking, and freezing temperatures are typically given in degrees Fahrenheit. Scientists, such as meteorologists, use degrees Celsius or kelvin in all countries. [16]

Early in the 20th 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. [17]

Canada has passed legislation favoring the International System of Units, while also maintaining legal definitions for traditional Canadian imperial units. [18] Canadian weather reports are conveyed using degrees Celsius with occasional reference to Fahrenheit especially for cross-border broadcasts. Fahrenheit is still used on virtually all Canadian ovens, [19] and in reference to swimming pool temperatures and thermostats.[ citation needed ] Thermometers, both digital and analog, sold in Canada usually employ both the Celsius and Fahrenheit scales. [20] [21] [22]

European laundry symbol for "Wash at 40 degC" Waschen 40.svg
European laundry symbol for "Wash at 40 °C"

In 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. [23] 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. [24] The equivalent label in North America uses one to six dots to denote temperature with an optional temperature in degrees Celsius. [25] [26]

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, [27] The Daily Telegraph does not mention Fahrenheit on its daily weather page [28] while The Times also has an all-metric daily weather page but has a Celsius-to-Fahrenheit conversion table. [29] When publishing news stories, much of the UK press have adopted a tendency of using degrees Celsius in headlines and discussion relating to low temperatures and Fahrenheit for high temperatures. [30] [ discuss ] In February 2006, the writer of an article in The Times suggested that the rationale was one of emphasis: "−6 °C" sounds colder than "21 °F" and "94 °F" sounds more impressive than "34 °C". [31]

Unicode representation of symbol

Unicode provides the Fahrenheit symbol at code point U+2109DEGREE 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+0046FLATIN CAPITAL LETTER F is preferred over U+2109DEGREE FAHRENHEIT, and those two sequences should be treated as identical for searching." [32]

See also

Notes and references

  1. Robert T. Balmer (2010). Modern Engineering Thermodynamics. Academic Press. p. 9. ISBN   978-0-12-374996-3 . Retrieved 17 July 2011.
  2. "Fahrenheit: Facts, History & Conversion Formulas". Live Science. Retrieved 9 February 2018.
  3. Fahrenheit temperature scale, Encyclopædia Britannica Online. 25 September 2015
  4. 1 2 Walt Boyes (2009). Instrumentation Reference Book. Butterworth-Heinemann. pp. 273–274. ISBN   978-0-7506-8308-1 . Retrieved 17 July 2011.
  5. Preston–Thomas, H. (1990). "The International Temperature Scale of 1990 (ITS-90)" (PDF). Metrologia. 27 (1): 6. Bibcode:1990Metro..27....3P. doi:10.1088/0026-1394/27/1/002 . Retrieved 17 July 2011.
  6. "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)
  7. Fahrenheit, Daniele Gabr. (1724) Experimenta & observationes de congelatione aquæ in vacuo factæ a D. G. Fahrenheit, R. S. S (Experiments and observations on water freezing in the void by D. G. Fahrenheit, R. S. S.), Philosophical Transactions of the Royal Society of London, vol. 33, no. 382, page 78 (March-April 1724). Cited and translated in http://www.sizes.com:80/units/temperature_Fahrenheit.htm
  8. "Wetterlexikon - Lufttemperatur" (in German). Deutscher Wetterdienst. Archived from the original on 15 October 2013. Retrieved 13 December 2013.
  9. 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
  10. Frautschi, Steven C.; Richard P. Olenick; Tom M. Apostol; David L. Goodstein (14 January 2008). The mechanical universe: mechanics and heat. Cambridge University Press. p. 502. ISBN   978-0-521-71590-4.
  11. Cecil Adams (15 December 1989). "On the Fahrenheit scale, do 0 and 100 have any special significance?". The Straight Dope.
  12. Fahrenheit, Daniele Gabr. (1724) "Experimenta circa gradum caloris liquorum nonnullorum ebullientium instituta" Archived 29 June 2014 at the Wayback Machine (Experiments performed concerning the degree of heat of some boiling liquids), Philosophical Transactions of the Royal Society of London, 33 : 1–3. For an English translation, see: Le Moyne College (Syracuse, New York)
  13. Hasok Chang, Inventing Temperature: Measurement and Scientific Progress, pp. 8–11, Oxford University Press, 2004 ISBN   0198038240.
  14. Elert, Glenn; Forsberg, C; Wahren, LK (2002). "Temperature of a Healthy Human (Body Temperature)". Scandinavian Journal of Caring Sciences. 16 (2): 122–8. doi:10.1046/j.1471-6712.2002.00069.x. PMID   12000664. Archived from the original on 26 September 2010. Retrieved 12 April 2008.
  15. Eutectic temperature of ammonium chloride and water is listed as −15.9 °C (3.38 °F) and as −15.4 °C (4.28 °F) in (respectively)
  16. "782 - Aerodrome reports and forecasts: A user's handbook to the codes". World Meteorological Organization. Retrieved 23 September 2009.
  17. Halsey, Frederick A., Dale, Samuel S. (1919). The metric fallacy (2 ed.). The American Institute of Weights and Measures. pp. 165–166, 176–177. Retrieved 19 May 2009.CS1 maint: Multiple names: authors list (link)
  18. "Canadian Units of Measurement; Department of Justice, Weights and Measures Act (R.S.C., 1985, c. W-6)". 17 May 2011. Archived from the original on 13 May 2011. Retrieved 5 June 2011.
  19. Pearlstein, Steven (4 June 2000). "Did Canada go metric? Yes - and no". The Seattle Times. Retrieved 5 June 2011.
  20. "Example of analog thermometer frequently used in Canada". Archived from the original on 6 July 2011. Retrieved 6 June 2011.
  21. "Example of digital thermometer frequently used in Canada". Archived from the original on 6 July 2011. Retrieved 6 June 2011.
  22. Department of Justice (26 February 2009). "Canadian Weights and Measures Act". Federal Government of Canada. Archived from the original on 10 August 2011. Retrieved 17 July 2011.
  23. Statutory Instrument 2009/3046 - Weights and Measures - The Units of Measurement Regulations 2009 (PDF), archived from the original (PDF) on 1 January 2017, "The Secretary of State, being a Minister designated(a) for the purposes of section 2(2) of the European Communities Act 1972(b) in relation to units of measurement to be used for economic, health, safety, or administrative purposes, in exercise of the powers conferred by that subsection, makes the following Regulations:
  24. "Home Laundering Consultative Council - What Symbols Mean". Home Laundering Consultative Council. Retrieved 15 July 2013.
  25. "Guide to Common Home Laundering & Drycleaning Symbols". Textile Industry Affairs. 2010. Retrieved 15 July 2013.
  26. "Guide to Apparel and Textile Care Symbols". Office of Consumer Affairs, Government of Canada. 17 April 2003. Retrieved 15 July 2013.
  27. "Weather". The Daily Mail. 3 July 2013. p. 3.
  28. "Weather". The Daily Telegraph. 3 July 2013. p. 31.
  29. "Weather". The Times. 3 July 2013. p. 55.
  30. Roy Greenslade (29 May 2014). "Newspapers run hot and cold over Celsius and Fahrenheit". The Guardian.
  31. "Measure for measure". The Times. Times Newspapers. 23 February 2006.
  32. "22.2". The Unicode Standard, Version 8.0 (PDF). Mountain View, CA, USA: The Unicode Consortium. August 2015. ISBN   978-1-936213-10-8 . Retrieved 6 September 2015.

Related Research Articles

Anders Celsius Swedish astronomer, physicist, and naturalist (1701-1744)

Anders Celsius was a Swedish astronomer, physicist and mathematician. He was professor of astronomy at Uppsala University from 1730 to 1744, but traveled from 1732 to 1735 visiting notable observatories in Germany, Italy and France. He founded the Uppsala Astronomical Observatory in 1741, and in 1742 proposed the Celsius temperature scale which bears his name.

The Rankine scale is an absolute scale of thermodynamic temperature named after the Glasgow University engineer and physicist William John Macquorn Rankine, who proposed it in 1859. It may be used in engineering systems where heat computations are done using degrees Fahrenheit.

Thermodynamic temperature Absolute measure of temperature

Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics.

Timeline of temperature and pressure measurement technology. A history of temperature measurement and pressure measurement technology.

Mercury-in-glass thermometer Type of thermometer

The mercury-in-glass or mercury thermometer was invented by physicist Daniel Gabriel Fahrenheit in Amsterdam (1714). It consists of a bulb containing mercury attached to a glass tube of narrow diameter; the volume of mercury in the tube is much less than the volume in the bulb. The volume of mercury changes slightly with temperature; the small change in volume drives the narrow mercury column a relatively long way up the tube. The space above the mercury may be filled with nitrogen gas or it may be at less than atmospheric pressure, a partial vacuum.

Réaumur scale temperature scale

The Réaumur scale, also known as the "octogesimal division", is a temperature scale for which the freezing and boiling points of water are defined as 0 and 80 degrees respectively. The scale is named for René Antoine Ferchault de Réaumur, who first proposed a similar scale in 1730.

The Rømer scale, also known as Romer or Roemer, is a temperature scale named after the Danish astronomer Ole Christensen Rømer, who proposed it in 1701. It is based on the freezing point of pure water being 7.5 degrees and the boiling point of water as 60 degrees.

The Delisle scale (°D) is a temperature scale invented in 1732 by the French astronomer Joseph-Nicolas Delisle (1688–1768). Delisle was the author of Mémoires pour servir à l'histoire et aux progrès de l'Astronomie, de la Géographie et de la Physique (1738).

The Newton scale is a temperature scale devised by Isaac Newton in 1701. He called his device a "thermometer", but he did not use the term "temperature", speaking of "degrees of heat" instead. Newton's publication represents the first attempt to introduce an objective way of measuring temperature . Newton likely developed his scale for practical use rather than for a theoretical interest in thermodynamics; he had been appointed Warden of the Mint in 1695, and Master of the Mint in 1699, and his interest in the boiling points of metals are likely inspired by his duties in connection with the Royal Mint.

The term degree is used in several scales of temperature. The symbol ° is usually used, followed by the initial letter of the unit, for example “°C” for degree(s) Celsius. A degree can be defined as a set change in temperature measured against a given scale, for example, one degree Celsius is one hundredth of the temperature change between the point at which water starts to change state from solid to liquid state and the point at which it starts to change from its gaseous state to liquid.

The International Temperature Scale of 1990 (ITS-90) published by the Consultative Committee for Thermometry (CCT) of the International Committee for Weights and Measures (CIPM) is an equipment calibration standard for making measurements on the Kelvin and Celsius temperature scales. ITS-90 is an approximation of the thermodynamic temperature scale that facilitates the comparability and compatibility of temperature measurements internationally. It specifies fourteen calibration points ranging from 0.65±0 K to 1357.77±0 K and is subdivided into multiple temperature ranges which overlap in some instances. ITS-90 is the latest of a series of International Temperature Scales adopted by CIPM since 1927. Adopted at the 1989 General Conference on Weights and Measures, it supersedes the International Practical Temperature Scale of 1968 and the 1976 "Provisional 0.5 K to 30 K Temperature Scale". CCT has also adopted a mise en pratique in 2011. The lowest temperature covered by ITS-90 is 0.65 K. In 2000, the temperature scale was extended further, to 0.9 mK, by the adoption of a supplemental scale, known as the Provisional Low Temperature Scale of 2000 (PLTS-2000).

A medical thermometer is used for measuring human or animal body temperature. The tip of the thermometer is inserted into the mouth under the tongue, under the armpit, or into the rectum via the anus.

Degree of frost

A degree of frost is a non-standard unit of measure for air temperature meaning degrees below melting point of water. "Degree" in this case can refer to degree Celsius or degree Fahrenheit.

Celsius Scale and unit of measurement for temperature

The Celsius scale, also known as the centigrade scale, is a temperature scale used by the International System of Units (SI). As an SI derived unit, it is used by all countries except the United States, the Bahamas, Belize, the Cayman Islands and Liberia. It is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale. The degree Celsius can refer to a specific temperature on the Celsius scale or a unit to indicate a difference between two temperatures or an uncertainty. Before being renamed to honor Anders Celsius in 1948, the unit was called centigrade, from the Latin centum, which means 100, and gradus, which means steps.

Temperature physical property of matter that quantitatively expresses the common notions of hot and cold

Temperature is a physical quantity expressing hot and cold. It is measured with a thermometer calibrated in one or more temperature scales. The most commonly used scales are the Celsius scale, Fahrenheit scale, and Kelvin scale. The kelvin is the unit of temperature in the International System of Units (SI), in which temperature is one of the seven fundamental base quantities. The Kelvin scale is widely used in science and technology.

An absolute scale is a system of measurement that begins at a minimum, or zero point, and progresses in only one direction. An absolute scale differs from an arbitrary, or "relative," scale, which begins at some point selected by a person and can progress in both directions. An absolute scale begins at a natural minimum, leaving only one direction in which to progress.