The CELSIUS SCALE, also known as the CENTIGRADE SCALE, is an SI
scale and unit of measurement for temperature . As an SI derived unit
, it is used by most countries in the world. It is named after the
Anders Celsius (1701–1744), who developed a
similar temperature scale. The DEGREE CELSIUS (symbol: °C) can refer
to a specific temperature on the
Thus, a temperature difference of one degree
* 1 History
* 1.1 Centigrade, hectograde and
* 2 Name and symbol typesetting
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 which was the reverse of the scale now known by the
name "Celsius": 0 represented the boiling point of water, while 100
represented the freezing point of water. 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 .
In 1743, the Lyonnais physicist Jean-Pierre Christin , permanent secretary of the Académie des sciences, belles-lettres et arts de LyonFR, working independently of Celsius, developed a scale where zero represented the freezing point of water and 100 represented the boiling point of water. 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.
In 1744, coincident with the death of Anders Celsius, the Swedish botanist Carolus Linnaeus (1707–1778) reversed Celsius's scale. 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 and 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; 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, the instrument maker; and Mårten Strömer (1707–1770) who had studied astronomy under Anders Celsius.
The first known Swedish document reporting temperatures in this
...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 referred to this scale as the centigrade scale. 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 (1/100 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
To eliminate such confusion, the 9th CGPM and the CIPM (Comité international des poids et mesures ) formally adopted "degree Celsius" in 1948, 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" otherwise continuing to be in common but decreasing use, especially in informal contexts in English-speaking countries. It was not until February 1985 that the forecasts issued by the BBC switched from "centigrade" to "Celsius".
Some key temperatures relating the
Key scale relations
KELVIN CELSIUS FAHRENHEIT
Absolute zero (precisely, by definition) 0 K −273.15 °C −459.67 °F
Boiling point of liquid nitrogen 77.4 K −195.8 °C −320.4 °F
Sublimation point of dry ice . 195.1 K −78 °C −108.4 °F
Melting point of H2O (purified ice) 273.1499 K −0.0001 °C 31.9998 °F
Water's triple point (precisely, by definition) 273.16 K 0.01 °C 32.018 °F
Normal human body temperature (approximate average) 310.15 K 37.0 °C 98.6 °F
Water's boiling point at 1 atm (101.325 kPa) (approximate: see Boiling point ) 373.1339 K 99.9839 °C 211.971 °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
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"). Thus the value of the quantity is the product of the number and the unit, the space being regarded as a multiplication sign (just as a space between units implies multiplication). 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. Other languages, and various publishing houses, may follow different typographical rules.
Shown below is the degree
When viewed on computers that properly support Unicode, the above line may be similar to the image in the line below (enlarged for clarity):
The canonical decomposition is simply an ordinary degree sign and
"C", so some browsers may simply display "°C" in its place due to
TEMPERATURES AND INTERVALS
What is often confusing about the
COEXISTENCE OF KELVIN AND CELSIUS SCALES
In science and in engineering, the
Notwithstanding the official endorsement provided by decision #3 of Resolution 3 of the 13th CGPM, 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
One effect of defining the
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