This Day in History: Jean-Pierre Christin developed the centigrade/celsius temperature scale on this day (May 19) in 1743. Or, more accurately, he reversed the temperature scale developed by Anders Celsius. Since 1743 the Celsius scale has been based on 0 °C for the freezing point of water and 100 °C for the boiling point of water at 1 atm pressure. Prior to 1743 the values were reversed (i.e. the boiling point was 0 degrees and the freezing point was 100 degrees). The 1743 scale reversal was proposed by Jean-Pierre Christin.
The boiling point 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. The point where liquid become stable is called the triple point, where all three phases (solid, liquid and gas) are all in equilibrium.
The Fahrenheit scale is a temperature scale based on one proposed in 1724 by the physicist Daniel Gabriel Fahrenheit (1686–1736). Historically, on the Fahrenheit scale the melting point of water was 32°F and the boiling point was 212°F (at standard atmospheric pressure). This put the boiling and freezing points of water 180 degrees apart.
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 and in certain cases, the United Kingdom—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 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, including meteorologists, use degrees Celsius or kelvin in all countries.
The formula to convert Celsius to Fahrenheit is [°F] = [°C] × 9/5 + 32. For instance, take 20 degrees Celsius, multiply it by 9, divide it by 5 and add 32, and you get 68 degrees Fahrenheit.
The Fahrenheit and Celsius scales have one point at which they intersect. They are equal at -40 °C and -40 °F.
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