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The degree Celsius (°C) can refer to a specific temperature on the Celsius scale as well as a unit to indicate a temperature interval (a difference between two temperatures). From 1744 until 1954, 0 °C was defined as the freezing point of water and 100 °C was defined as the boiling point of water, both at a pressure of one standard atmosphere .
1742 — Anders Celsius proposed a temperature scale in which 100 represented the temperature of melting ice and 0 represented the boiling point of water at 25 inches and 3 lines of barometric mercury height. [8] This corresponds to 751.16 mm, [9] so that on the present-day definition, this boiling point is 99.67 degrees Celsius. [10]
Anders Celsius's original thermometer used a reversed scale, with 100 as the freezing point and 0 as the boiling point of water.. 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. [5]
To convert a delta temperature from degrees Fahrenheit to degrees Celsius, the formula is {ΔT} °F = 9 / 5 {ΔT} °C. To convert a delta temperature from degrees Celsius to kelvin, it is 1:1 ({ΔT} °C = {ΔT} K).
With the Fahrenheit and Celsius scales now both defined by the kelvin, this relationship was preserved, a temperature interval of 1 °F being equal to an interval of 5 ⁄ 9 K and of 5 ⁄ 9 °C. The Fahrenheit and Celsius scales intersect numerically at −40 in the respective unit (i.e., −40 °F ≘ −40 °C).
[1]: 19 The development of today's thermometers and temperature scales began in the early 18th century, when Daniel Gabriel Fahrenheit produced a mercury thermometer and scale, both developed by Ole Christensen Rømer. Fahrenheit's scale is still in use, alongside the Celsius and Kelvin scales.
At the 9th CGPM, the Celsius temperature scale was renamed the Celsius scale, and the scale itself was fixed by defining the triple point of water as 0.01 °C, [81] though the CGPM left the formal definition of absolute zero until the 10th CGPM when the name "Kelvin" was assigned to the absolute temperature scale, and the triple point of water ...
It is because of the scale's redefinition that normal mean body temperature today is taken as 98.6 degrees, [17] whereas it was 96 degrees on Fahrenheit's original scale. [18] The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes in English-speaking countries until the 1970s, presently mostly ...