Mercury-in-glass thermometer ushered in a new era of accuracy and precision in thermometry, and is still to this day regarded as one of the most accurate thermometers available. The thermometer was used by the originators of the Fahrenheit and Celsius scales. Anders Celsius, a Swedish scientist, devised the Celsius scale, which was described in his publication "The origin of the Celsius temperature scale" in 1742. Celsius used two fixed points in his scale: the temperature of melting ice and the temperature of boiling water. This wasn't a new idea, since Isaac Newton was already working on something similar. The distinction of Celsius
Scale of temperature is the function of the temperatures only: In addition, a reversible heat engine operating between temperatures "T" and "T" must have the same efficiency as one consisting of two cycles, one between "T" and another (intermediate) temperature "T", and the second between "T" and "T". This can only be the case if Specializing to the case that formula_5 is a fixed reference temperature: the temperature of the triple point of water. Then for any "T" and "T", Therefore, if thermodynamic temperature is defined by then the function "f", viewed as a function of thermodynamic temperature, is and the reference temperature