Science History of Temperature

About the history of temperature and the Farenheit, Celsius and Kelvin scales.


Attempts to measure temperature accurately began with Galileo's thermoscope. This was followed by the thermometers constructed by Jean Rey, the Accademia del Cimento of Florence, Guillaume Amontons, and a host of others.

In 1724 Gabriel Daniel Fahrenheit developed the temperature scale used in the U.S. and a few other countries today. A distinct advance, it had a fixed reference point that could be verified by anyone, anywhere: human body temperature. Fahrenheit called this a very approximate 96 deg, since 96 deg. is an easily divisible integer. Then he assigned the melting point of ice at 32 degrees on his scale, and the boiling point of water at 212.

In 1730 R. A. F. de Reaumur developed a scale using water's freezing and boiling points as references. Reaumur divided the scale between freezing and boiling into 80 deg.s. This scale is still used in some places in Europe.

The scale in widest use throughout the world was developed in 1742 by Anders Celsius. He called the freezing point of water 0 deg. and the boiling point 100 deg., and divided the scale between them into 100 degrees. This is known as the Centigrade, or alternatively the Celsius, scale.

The Kelvin scale, invented in 1848, is the scale used in the physical sciences. Its degrees are the same size as those of the Centigrade scale, but its zero point has been moved down to the theoretical lowest possible temperature in the universe: absolute zero (the point at which the volume of any gas would be reduced to zero). On the Kelvin scale (which does not use degree signs with numbers), water freezes at 273.15 and boils at 373.15.

The United States, along with other English-speaking nations, will soon be changing from the Fahrenheit scale to the Centigrade scale. To convert a Fahrenheit temperature reading to Centigrade, first subtract 32 deg, since the Centigrade scale places water's freezing point at 0 deg, not 32 deg. Then multiply the remainder by 5/9, because there are 5/9 as many degrees between water's freezing and boiling points on the Centigrade scale. These formulas summarize scale conversions between Fahrenheit and Centigrade:

Centigrade = 5/9 (Fahrenheit - 32deg)

Fahrenheit = 9/5 Centigrade + 32deg

Also: Kelvin = Centigrade + 273.15, and Reaumur = 4/5 Centigrade.

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