![]() In 1743, the Lyonnais physicist Jean-Pierre Christin, permanent secretary of the Academy of Lyon, inverted the Celsius scale so that 0 represented the freezing point of water and 100 represented the boiling point of water. The BIPM's 10th General Conference on Weights and Measures (CGPM) in 1954 defined one standard atmosphere to equal precisely 1,013,250 dynes per square centimeter (101.325 kPa). This pressure is known as one standard atmosphere. 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. He also determined with remarkable precision how the boiling point of water varied as a function of atmospheric pressure. 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. 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. Note the reversed scale, where 100 is the freezing point of water and 0 is its boiling point. History An illustration of Anders Celsius's original thermometer. The temperature in degree Celsius is now defined as the temperature in kelvins subtracted by 273.15, meaning that a temperature difference of one degree Celsius and that of one kelvin are exactly the same, and that the degree Celsius remains exactly equal to the kelvin (i.e., 0 ☌ remains exactly 273.15 K). 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. This means that the triple point is now a measured value, not a defined value. On, the kelvin was redefined so that its value is now determined by the definition of the Boltzmann constant rather than being defined by the triple point of VSMOW. Until, the temperature of the triple point of water was defined as exactly 273.16 K (0.01 ☌). Absolute zero, the lowest temperature possible, is defined as being exactly 0 K and −273.15 ☌. ![]() ![]() This definition also precisely related the Celsius scale to the scale of the kelvin, the SI base unit of thermodynamic temperature with symbol K. After 2007, it was clarified that this definition referred to Vienna Standard Mean Ocean Water (VSMOW), a precisely defined water standard. The 1743 scale reversal was proposed by Jean-Pierre Christin.īy international agreement, between 19 the unit degree Celsius and the Celsius scale were defined by absolute zero and the triple point of water. the boiling point was 0 degrees and the freezing point was 100 degrees). Prior to 1743 the values were reversed (i.e. Since 1743, the Celsius scale has been based on 0 ☌ for the freezing point of water and 100 ☌ for the boiling point of water at 1 atm pressure. The Kelvin scale is of use in the sciences, with 0 K (−273.15 ☌) representing absolute zero. Most countries use this scale the other major scale, Fahrenheit, is still used in the United States, some island territories, and Liberia. In 1948, the International Committee for Weights and Measures renamed it to honor Celsius and also to remove confusion with the term for one hundredth of a gradian in some languages. ![]() The unit was called centigrade in several languages (from the Latin centum, which means 100, and gradus, which means steps) for many years. It is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a variant of it in 1742. The degree Celsius (symbol: ☌) can refer to a specific temperature on the Celsius scale or a unit to indicate a difference or range between two temperatures. The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. A thermometer calibrated in degrees Celsius, showing a temperature of −17 ☌
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