Celsius

Last updated

Celsius
Pakkanen.jpg
A thermometer calibrated in degrees Celsius
General information
Unit system SI derived unit
Unit ofTemperature
Symbol°C
Named after Anders Celsius
Conversions
x °C in ...... is equal to ...
    K    x + 273.15
    °F    (x × 9/5) + 32

The Celsius scale, also known as the centigrade scale, [1] [2] is a temperature scale used by the International System of Units (SI). As an SI derived unit, it is used worldwide. In the United States, [3] the Bahamas, Belize, the Cayman Islands and Liberia however, Fahrenheit remains the preferred scale for everyday temperature measurement. The degree Celsius (symbol: °C) can refer to a specific temperature on the Celsius scale or a unit to indicate a difference between two temperatures or an uncertainty. It is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale. 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.

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.

International System of Units a system of units of measurement for base and derived physical quantities

The International System of Units is the modern form of the metric system and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units, which are the second, metre, kilogram, ampere, kelvin, mole, candela, and a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system also specifies names for 22 derived units, such as lumen and watt, for other common physical quantities.

SI derived units are units of measurement derived from the seven base units specified by the International System of Units (SI). They are either dimensionless or can be expressed as a product of one or more of the base units, possibly scaled by an appropriate power of exponentiation.

Contents

By international agreement, from 1743 through mid 2019, the degree Celsius and the Celsius scale depended upon measurements of the triple point of Vienna Standard Mean Ocean Water (VSMOW), a precisely defined water standard. On 20 May 2019, the kelvin was redefined so that its value is now determined by the definition of the Boltzmann constant. This means that the triple point is now a measured value, not a defined value. The newly-defined exact value of the Boltzmann constant was selected so that the measured value of the VSMOW triple point is exactly the same as the older defined value to within the limits of accuracy of contemporary metrology. The degree Celsius remains exactly equal to the kelvin, and 0 K remains exactly −273.15 °C.

Vienna Standard Mean Ocean Water A standard defining the isotopic composition of fresh water originating from ocean water

Vienna Standard Mean Ocean Water (VSMOW) is an isotopic standard for water. Despite the name, VSMOW is pure water with no salt or other chemicals found in the oceans. The VSMOW standard was promulgated by the International Atomic Energy Agency in 1968, and since 1993 continues to be evaluated and studied by the IAEA along with the European Institute for Reference Materials and Measurements and the American National Institute of Standards and Technology. The standard includes both the established values of stable isotopes found in waters and calibration materials provided for standardization and interlaboratory comparisons of instruments used to measure these values in experimental materials.

The Boltzmann constant, named after its discoverer, Ludwig Boltzmann, is a physical constant that relates the average relative kinetic energy of particles in a gas with the temperature of the gas. It occurs in the definitions of the kelvin and the gas constant, and in Planck's law of black-body radiation and Boltzmann's entropy formula. The Boltzmann constant has the dimension energy divided by temperature, the same as entropy.

Metrology Science of measurement and its application

Metrology is the science of measurement. It establishes a common understanding of units, crucial in linking human activities. Modern metrology has its roots in the French Revolution's political motivation to standardise units in France, when a length standard taken from a natural source was proposed. This led to the creation of the decimal-based metric system in 1795, establishing a set of standards for other types of measurements. Several other countries adopted the metric system between 1795 and 1875; to ensure conformity between the countries, the Bureau International des Poids et Mesures (BIPM) was established by the Metre Convention. This has evolved into the International System of Units (SI) as a result of a resolution at the 11th Conference Generale des Poids et Mesures (CGPM) in 1960.

History

An illustration of Anders Celsius's original thermometer. Note the reversed scale, where 100 is the freezing point of water and 0 is its boiling point. Celsius original thermometer.png
An illustration of Anders Celsius's original thermometer. Note the reversed scale, where 100 is the freezing point of water and 0 is its boiling point.

In 1742, Swedish astronomer Anders Celsius (1701–1744) created a temperature scale that was the reverse of the scale now known as "Celsius": 0 represented the boiling point of water, while 100 represented the freezing point of water. [4] In his paper Observations of two persistent degrees on a thermometer, he recounted his experiments showing that the melting point of ice is essentially unaffected by pressure. He also determined with remarkable precision how the boiling point of water varied as a function of atmospheric pressure. He proposed that the zero point of his temperature scale, being the boiling point, would be calibrated at the mean barometric pressure at mean sea level. This pressure is known as one standard atmosphere. The BIPM's 10th General Conference on Weights and Measures (CGPM) later defined one standard atmosphere to equal precisely 1,013,250 dynes per square centimeter (101.325  kPa). [5]

Anders Celsius Swedish astronomer and physicist

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 standard atmosphere is a unit of pressure defined as 101325 Pa. It is sometimes used as a reference or standard pressure. It is approximately equal to the atmospheric pressure at sea level.

International Bureau of Weights and Measures an intergovernmental organization established by the Metre Convention, through which Member States act together on matters related to measurement science and measurement standards (BIPM)

The International Bureau of Weights and Measures is an intergovernmental organisation that was established by the Metre Convention, through which member states act together on matters related to measurement science and measurement standards. The organisation is usually referred to by its French initialism, BIPM. The BIPM's secretariat and formal meetings are housed in the organisations headquarters in Sèvres, France.

In 1743, the Lyonnais physicist Jean-Pierre Christin, permanent secretary of the Académie des sciences, belles-lettres et arts de Lyon  [ fr ], working independently of Celsius, developed a scale where zero represented the freezing point of water and 100 represented the boiling point of water. [6] [7] On 19 May 1743 he published the design of a mercury thermometer, the "Thermometer of Lyon" built by the craftsman Pierre Casati that used this scale. [8] [9] [10]

Lyon Prefecture and commune in Auvergne-Rhône-Alpes, France

Lyon or Lyons is the third-largest city and second-largest urban area of France. It is located in the country's east-central part at the confluence of the rivers Rhône and Saône, about 470 km (292 mi) south from Paris, 320 km (199 mi) north from Marseille and 56 km (35 mi) northeast from Saint-Étienne. Inhabitants of the city are called Lyonnais.

Jean-Pierre Christin 18th-century French scientist

Jean-Pierre Christin was a French physicist, mathematician, astronomer and musician. His proposal in 1743 to reverse the Celsius thermometer scale was widely accepted and is still in use today.

In 1744, coincident with the death of Anders Celsius, the Swedish botanist Carl Linnaeus (1707–1778) reversed Celsius's scale. [11] His custom-made "linnaeus-thermometer", for use in his greenhouses, was made by Daniel Ekström, Sweden's leading maker of scientific instruments at the time, whose workshop was located in the basement of the Stockholm observatory. As often happened in this age before modern communications, numerous physicists, scientists, and instrument makers are credited with having independently developed this same scale; [12] among them were Pehr Elvius, the secretary of the Royal Swedish Academy of Sciences (which had an instrument workshop) and with whom Linnaeus had been corresponding; Daniel Ekström[[[SV]] [ sv ]], the instrument maker; and Mårten Strömer (1707–1770) who had studied astronomy under Anders Celsius.

Carl Linnaeus Swedish botanist, physician, and zoologist

Carl Linnaeus, also known after his ennoblement as Carl von Linné, was a Swedish botanist, zoologist, and physician who formalised binomial nomenclature, the modern system of naming organisms. He is known as the "father of modern taxonomy". Many of his writings were in Latin, and his name is rendered in Latin as Carolus Linnæus.

The first known Swedish document [13] reporting temperatures in this modern "forward" Celsius scale is the paper Hortus Upsaliensis dated 16 December 1745 that Linnaeus wrote to a student of his, Samuel Nauclér. In it, Linnaeus recounted the temperatures inside the orangery at the University of Uppsala Botanical Garden:

University of Uppsala Botanical Garden

The University of Uppsala Botanical Garden, near Uppsala Castle, is the principal botanical garden belonging to Uppsala University. It was created on land donated to the university in 1787 by Sweden's King Gustav III, who also laid the cornerstone of Linneanum, its orangery.

...since the caldarium (the hot part of the greenhouse) by the angle of the windows, merely from the rays of the sun, obtains such heat that the thermometer often reaches 30 degrees, although the keen gardener usually takes care not to let it rise to more than 20 to 25 degrees, and in winter not under 15 degrees...

Centigrade, hectograde and Celsius

Since the 19th century, the scientific and thermometry communities worldwide have used the phrase "centigrade scale".[ why? ]Temperatures on the centigrade scale were often reported simply as degrees or, when greater specificity was desired, as degrees centigrade (symbol: °C). Because the term centigrade was also the Spanish and French language name for a unit of angular measurement (1/10000 of a right angle) and had a similar connotation in other languages, the term centesimal degree (known as the gradian , "grad" or "gon": 1ᵍ = 0.9°, 100ᵍ = 90°) was used when very precise, unambiguous language was required by international standards bodies such as the BIPM. More properly, what was defined as "centigrade" then would now be "hectograde".

To eliminate any confusion, the 9th CGPM and the CIPM (Comité international des poids et mesures) formally adopted "degree Celsius" in 1948, [14] [lower-alpha 1] formally keeping the recognized degree symbol, rather than adopting the gradian/centesimal degree symbol.

For scientific use, "Celsius" is the term usually used, with "centigrade" remaining in common but decreasing use, especially in informal contexts in English-speaking countries. [15] It was not until February 1985 that the weather forecasts issued by the BBC switched from "centigrade" to "Celsius". [16]

Common temperatures

Some key temperatures relating the Celsius scale to other temperature scales are shown in the table below.

Key scale relations
Kelvin Celsius Fahrenheit
Absolute zero (exactly)0 K−273.15 °C−459.67 °F
Boiling point of liquid nitrogen 77.4 K−195.8 °C [17] −320.4 °F
Sublimation point of dry ice 195.1 K−78 °C−108.4 °F
Intersection of Celsius and Fahrenheit scales233.15 K−40 °C−40 °F
Melting point of H2O (purified ice) [18] 273.1499 K−0.0001 °C31.9998 °F
Room temperature (NIST standard) [19] 293.15 K20.0 °C68.0 °F
Normal human body temperature (average) [20] 310.15 K37.0 °C98.6 °F
Water's boiling point at 1 atm (101.325 kPa)
(approximate: see Boiling point) [lower-alpha 2]
373.1339 K99.9839 °C211.971 °F

Name and symbol typesetting

The "degree Celsius" has been the only SI unit whose full unit name contains an uppercase letter since the SI base unit for temperature, the kelvin, became the defined name in 1967 replacing the term degrees Kelvin. The plural form is degrees Celsius. [21]

The general rule of the International Bureau of Weights and Measures (BIPM) is that the numerical value always precedes the unit, and a space is always used to separate the unit from the number, e.g. "30.2 °C" (not "30.2°C" or "30.2° C"). [22] The only exceptions to this rule are for the unit symbols for degree, minute, and second for plane angle (°, ′, and ″, respectively), for which no space is left between the numerical value and the unit symbol. [23] Other languages, and various publishing houses, may follow different typographical rules.

Unicode character

Unicode provides the Celsius symbol at code point U+2103DEGREE CELSIUS. However, this is a compatibility character provided for roundtrip compatibility with legacy encodings. It easily allows correct rendering for vertically written East Asian scripts, such as Chinese. The Unicode standard explicitly discourages the use of this character: "In normal use, it is better to represent degrees Celsius "°C" with a sequence of U+00B0°DEGREE SIGN + U+0043CLATIN CAPITAL LETTER C, rather than U+2103DEGREE CELSIUS. For searching, treat these two sequences as identical." [24]

Temperatures and intervals

The degree Celsius is subject to the same rules as the kelvin with regard to the use of its unit name and symbol. Thus, besides expressing specific temperatures along its scale (e.g. "Gallium melts at 29.7646 °C" and "The temperature outside is 23 degrees Celsius"), the degree Celsius is also suitable for expressing temperature intervals: differences between temperatures or their uncertainties (e.g. "The output of the heat exchanger is hotter by 40 degrees Celsius", and "Our standard uncertainty is ±3 °C"). [25] Because of this dual usage, one must not rely upon the unit name or its symbol to denote that a quantity is a temperature interval; it must be unambiguous through context or explicit statement that the quantity is an interval. [lower-alpha 3] This is sometimes solved by using the symbol °C (pronounced "degrees Celsius") for a temperature, and C° (pronounced "Celsius degrees") for a temperature interval, although this usage is non-standard. [26] Another way to express the same is "40°C ± 3 K", which can be commonly found in literature.

Celsius measurement follows an interval system but not a ratio system; and it follows a relative scale not an absolute scale. For example, an object at 20 °C does not have twice the energy of when it is 10 °C; and 0 °C is not the lowest Celsius value. Thus, degrees Celsius is a useful interval measurement but does not possess the characteristics of ratio measures like weight or distance. [27]

Coexistence of Kelvin and Celsius scales

In science and in engineering, the Celsius scale and the Kelvin scale are often used in combination in close contexts, e.g. "a measured value was 0.01023 °C with an uncertainty of 70 µK". This practice is permissible because the magnitude of the degree Celsius is equal to that of the kelvin. Notwithstanding the official endorsement provided by decision #3 of Resolution 3 of the 13th CGPM, [28] which stated "a temperature interval may also be expressed in degrees Celsius", the practice of simultaneously using both °C and K remains widespread throughout the scientific world as the use of SI-prefixed forms of the degree Celsius (such as "µ°C" or "microdegrees Celsius") to express a temperature interval has not been well-adopted.

Melting and boiling points of water

The melting and boiling points of water are no longer part of the definition of the Celsius scale. In 1948, the definition was changed to use the triple point of water. [29] In 2005 the definition was further refined to use water with precisely defined isotopic composition (VSMOW) for the triple point. In 2019, the definition was changed to use the Boltzmann constant, completely decoupling the definition of the kelvin from the properties of water. Each of these formal definitions left the numerical values of the Celsius scale identical to the prior definition to within the limits of accuracy of the metrology of the time.

When the melting and boiling points of water ceased being part of the definition, they became measured quantities instead. This is also true of the triple point.

In 1948 when the 9th General Conference on Weights and Measures (CGPM) in Resolution 3 first considered using the triple point of water as a defining point, the triple point was so close to being 0.01 °C greater than water's known melting point, it was simply defined as precisely 0.01 °C. However, later measurements showed that the difference between the triple and melting points of VSMOW is actually very slightly (<0.001 °C) greater than 0.01 °C. Thus, the actual melting point of ice is very slightly (less than a thousandth of a degree) below 0 °C. Also, defining water's triple point at 273.16 K precisely defined the magnitude of each 1 °C increment in terms of the absolute thermodynamic temperature scale (referencing absolute zero). Now decoupled from the actual boiling point of water, the value "100 °C" is hotter than 0 °C – in absolute terms – by a factor of precisely373.15/273.15 (approximately 36.61% thermodynamically hotter). When adhering strictly to the two-point definition for calibration, the boiling point of VSMOW under one standard atmosphere of pressure was actually 373.1339 K (99.9839 °C). When calibrated to ITS-90 (a calibration standard comprising many definition points and commonly used for high-precision instrumentation), the boiling point of VSMOW was slightly less, about 99.974 °C. [30]

This boiling-point difference of 16.1 millikelvins between the Celsius scale's original definition and the previous one (based on absolute zero and the triple point) has little practical meaning in common daily applications because water's boiling point is very sensitive to variations in barometric pressure. For example, an altitude change of only 28 cm (11 in) causes the boiling point to change by one millikelvin.

Celsius temperature conversion formulae
from Celsiusto Celsius
Fahrenheit [°F] = [°C] × 95 + 32[°C] = ([°F]  32) × 59
Kelvin [K] = [°C] + 273.15[°C] = [K]  273.15
Rankine [°R] = ([°C] + 273.15) × 95[°C] = ([°R]  491.67) × 59
For temperature intervals rather than specific temperatures,
1 °C = 1 K = 95 °F = 95 °R
Comparisons among various temperature scales

See also

Notes

  1. According to The Oxford English Dictionary (OED), the term "Celsius' thermometer" had been used at least as early as 1797. Further, the term "The Celsius or Centigrade thermometer" was again used in reference to a particular type of thermometer at least as early as 1850. The OED also cites this 1928 reporting of a temperature: "My altitude was about 5,800 metres, the temperature was 28° Celsius." However, dictionaries seek to find the earliest use of a word or term and are not a useful resource as regards to the terminology used throughout the history of science. According to several writings of Dr. Terry Quinn CBE FRS, Director of the BIPM (1988–2004), including "Temperature Scales from the early days of thermometry to the 21st century" (PDF). (146  KiB) as well as Temperature (2nd Edition/1990/Academic Press/0125696817), the term Celsius in connection with the centigrade scale was not used whatsoever by the scientific or thermometry communities until after the CIPM and CGPM adopted the term in 1948. The BIPM was not even aware that "degree Celsius" was in sporadic, non-scientific use before that time. It is also noteworthy that the twelve-volume, 1933 edition of OED didn't even have a listing for the word Celsius (but did have listings for both centigrade and centesimal in the context of temperature measurement). The 1948 adoption of Celsius accomplished three objectives:
    1.    All common temperature scales would have their units named after someone closely associated with them; namely, Kelvin, Celsius, Fahrenheit, Réaumur and Rankine.
    2.    Notwithstanding the important contribution of Linnaeus who gave the Celsius scale its modern form, Celsius's name was the obvious choice because it began with the letter C. Thus, the symbol °C that for centuries had been used in association with the name centigrade could remain in use and would simultaneously inherit an intuitive association with the new name.
    3.    The new name eliminated the ambiguity of the term "centigrade", freeing it to refer exclusively to the French-language name for the unit of angular measurement.
  2. For Vienna Standard Mean Ocean Water at one standard atmosphere (101.325 kPa) when calibrated solely per the two-point definition of thermodynamic temperature. Older definitions of the Celsius scale once defined the boiling point of water under one standard atmosphere as being precisely 100 °C. However, the current definition results in a boiling point that is actually 16.1 mK less. For more about the actual boiling point of water, see VSMOW in temperature measurement. A different approximation uses ITS-90, which approximates the temperature to 99.974 °C
  3. In 1948, Resolution 7 of the 9th CGPM stated, "To indicate a temperature interval or difference, rather than a temperature, the word 'degree' in full, or the abbreviation 'deg' must be used." This resolution was abrogated in 1967/1968 by Resolution 3 of the 13th CGPM, which stated that ["The names "degree Kelvin" and "degree", the symbols "°K" and "deg" and the rules for their use given in Resolution 7 of the 9th CGPM (1948),] ...and the designation of the unit to express an interval or a difference of temperatures are abrogated, but the usages which derive from these decisions remain permissible for the time being." Consequently, there is now wide freedom in usage regarding how to indicate a temperature interval. The most important thing is that one's intention must be clear and the basic rule of the SI must be followed; namely that the unit name or its symbol must not be relied upon to indicate the nature of the quantity. Thus, if a temperature interval is, say, 10 K or 10 °C (which may be written 10 kelvins or 10 degrees Celsius), it must be unambiguous through obvious context or explicit statement that the quantity is an interval. Rules governing the expressing of temperatures and intervals are covered in the BIPM's "SI Brochure, 8th edition" (PDF). (1.39  MiB).

Related Research Articles

Fahrenheit unit of temperature

The Fahrenheit scale is a temperature scale based on one proposed in 1724 by German physicist Daniel Gabriel Fahrenheit (1686–1736). It uses the degree Fahrenheit as the unit. Several accounts of how he originally defined his scale exist. The lower defining point, 0 ℉, was established as the freezing temperature of a solution of brine made from equal parts of ice, water and a salt. Further limits were established as the melting point of ice (32 ℉) and his best estimate of the average human body temperature. The scale is now usually defined by two fixed points: the temperature at which water freezes into ice is defined as 32 ℉, and the boiling point of water is defined to be 212 ℉, a 180 ℉ separation, as defined at sea level and standard atmospheric pressure.

Kilogram SI unit of mass

The kilogram is the base unit of mass in the metric system, formally the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering, and commerce worldwide, and is often simply called a kilo in everyday speech.

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.

In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases of that substance coexist in thermodynamic equilibrium. It is that temperature and pressure at which the sublimation curve, fusion curve and the vaporisation curve meet. For example, the triple point of mercury occurs at a temperature of −38.83440 °C and a pressure of 0.2 mPa.

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.

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).

The standard acceleration due to gravity, sometimes abbreviated as standard gravity, usually denoted by ɡ0 or ɡn, is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth. It is defined by standard as 9.80665 m/s2. This value was established by the 3rd CGPM and used to define the standard weight of an object as the product of its mass and this nominal acceleration. The acceleration of a body near the surface of the Earth is due to the combined effects of gravity and centrifugal acceleration from the rotation of the Earth ; the total is about 0.5% greater at the poles than at the Equator.

The kelvin is the base unit of temperature in the International System of Units (SI), having the unit symbol K. It is named after the Belfast-born, Glasgow University engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907).

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

A temperature expresses hot and cold, as measured with a thermometer. In physics, hotness is a body's ability to impart energy as heat to another body that is colder.

2019 redefinition of the SI base units Redefinition of the SI base units kilogram, ampere, kelvin, and mole

In 2019, the SI base units were redefined, effective on 144th anniversary of the Metre Convention, 20 May 2019. In the redefinition, four of the seven SI base units – the kilogram, ampere, kelvin, and mole – were redefined by setting exact numerical values for the Planck constant, the elementary electric charge, the Boltzmann constant, and the Avogadro constant, respectively. The second, metre, and candela were already defined by physical constants and were subject to correction to their definitions. The new definitions aimed to improve the SI without changing the value of any units, ensuring continuity with existing measurements. In November 2018, the 26th General Conference on Weights and Measures (CGPM) unanimously approved these changes, which the International Committee for Weights and Measures (CIPM) had proposed earlier that year after determining that previously agreed conditions for the change had been met. These conditions were satisfied by a series of experiments that measured the constants to high accuracy relative to the old SI definitions, and were the culmination of decades of research.

The history of the metric system began in the Age of Enlightenment with notions of length and weight taken from natural ones, and decimal multiples and fractions of them. The system became the standard of France and Europe in half a century. Other dimensions with unity ratios were added, and it went on to be adopted by the world.

Introduction to the metric system

The metric system was developed during the French Revolution to replace the various measures previously used in France. The metre is the unit of length in the metric system and was originally based on the dimensions of the earth, as far as it could be measured at the time. The litre, is the unit of volume and was defined as one thousandth of a cubic metre. The metric unit of mass is the kilogram and it was defined as the mass of one litre of water. The metric system was, in the words of French philosopher Marquis de Condorcet, "for all people for all time".

References

  1. "Celsius temperature scale". Encyclopædia Britannica . Retrieved 19 February 2012. Celsius temperature scale, also called centigrade temperature scale, scale based on 0 ° for the melting point of water and 100 ° for the boiling point of water at 1 atm pressure.
  2. Helmenstine, Anne Marie (December 15, 2014). "What Is the Difference Between Celsius and Centigrade?". Chemistry.about.com. About.com. Retrieved March 16, 2015.
  3. https://www.vox.com/2015/2/16/8031177/america-fahrenheit
  4. Celsius, Anders (1742) "Observationer om twänne beständiga grader på en thermometer" (Observations about two stable degrees on a thermometer), Kungliga Svenska Vetenskapsakademiens Handlingar (Proceedings of the Royal Swedish Academy of Sciences), 3 : 171–180 and Fig. 1.
  5. "Resolution 4 of the 10th meeting of the CGPM (1954)".
  6. Don Rittner; Ronald A. Bailey (2005): Encyclopedia of Chemistry. Facts On File, Manhattan, New York City. p. 43.
  7. Smith, Jacqueline (2009). "Appendix I: Chronology". The Facts on File Dictionary of Weather and Climate. Infobase Publishing. p. 246. ISBN   978-1-4381-0951-0. 1743 Jean-Pierre Christin inverts the fixed points on Celsius' scale, to produce the scale used today.
  8. Mercure de France (1743): MEMOIRE sur la dilatation du Mercure dans le Thermométre. Chaubert; Jean de Nully, Pissot, Duchesne, Paris. pp. 1609–1610.
  9. Journal helvétique (1743): LION. Imprimerie des Journalistes, Neuchâtel. pp. 308–310.
  10. Memoires pour L'Histoire des Sciences et des Beaux Arts (1743): DE LYON. Chaubert, París. pp. 2125–2128.
  11. Citation: Uppsala University (Sweden), Linnaeus' thermometer
  12. Citation for Daniel Ekström, Mårten Strömer, Christin of Lyons: The Physics Hypertextbook, Temperature; citation for Christin of Lyons: Le Moyne College, Glossary, (Celsius scale); citation for Linnaeus's connection with Pehr Elvius and Daniel Ekström: Uppsala University (Sweden), Linnaeus' thermometer; general citation: The Uppsala Astronomical Observatory, History of the Celsius temperature scale
  13. Citations: University of Wisconsin–Madison, Linnæus & his Garden and; Uppsala University, Linnaeus' thermometer
  14. "CIPM, 1948 and 9th CGPM, 1948". International Bureau of Weights and Measures . Retrieved 9 May 2008.
  15. "centigrade, adj. and n." Oxford English Dictionary. Oxford University Press. Retrieved 20 November 2011.
  16. 1985 BBC Special: A Change In The Weather on YouTube
  17. Lide, D.R., ed. (1990–1991). Handbook of Chemistry and Physics. 71st ed. CRC Press. p. 4–22.
  18. The ice point of purified water has been measured at 0.000089(10) degrees Celsius – see Magnum, B.W. (June 1995). "Reproducibility of the Temperature of the Ice Point in Routine Measurements" (PDF). Nist Technical Note. 1411. Archived from the original (PDF) on July 14, 2007. Retrieved 11 February 2007.
  19. "SI Units - Temperature". 2010. Retrieved 7 November 2019.
  20. Elert, Glenn (2005). "Temperature of a Healthy Human (Body Temperature)". The Physics Factbook. Retrieved 22 August 2007.
  21. "Unit of thermodynamic temperature (kelvin)". The NIST Reference on Constants, Units, and Uncertainty: Historical context of the SI. National Institute of Standards and Technology (NIST). 2000. Retrieved 16 November 2011.
  22. BIPM, SI Brochure, Section 5.3.3.
  23. For more information on conventions used in technical writing, see the informative SI Unit rules and style conventions by the NIST as well as the BIPM's SI brochure: Subsection 5.3.3, Formatting the value of a quantity. Archived 2014-07-05 at the Wayback Machine
  24. "22.2". The Unicode Standard, Version 9.0 (PDF). Mountain View, CA, USA: The Unicode Consortium. July 2016. ISBN   978-1-936213-13-9 . Retrieved 20 April 2017.
  25. Decision #3 of Resolution 3 of the 13th CGPM.
  26. H.D. Young, R. A. Freedman (2008). University Physics with Modern Physics (12th ed.). Addison Wesley. p. 573.
  27. This fact is demonstrated in the book Biostatistics: A Guide to Design, Analysis, and Discovery By Ronald N. Forthofer, Eun Sul Lee and Mike Hernandez
  28. http://www.bipm.fr/en/CGPM/db/13/3/
  29. "Resolution 3 of the 9th CGPM (1948)". International Bureau of Weights and Measures . Retrieved 9 May 2008.
  30. Citation: London South Bank University, Water Structure and Behavior, notes c1 and c2

Wiktionary-logo-en-v2.svg The dictionary definition of Celsius at Wiktionary