An odd thermometer invented in 1731 by René-Antoine Ferchault de Réaumur, a French naturalist with the sort of aristocratic name that would become wildly unfashionable after the Revolution.

It measured temperature on a scale (also named Réaumur) in which the freezing point of water was 0 degrees and the boiling point 80 degrees, at a standard pressure of one atmosphere. As one historian notes, "The gradation of temperature scales is arbitrary and Reaumur was an arbitrary scientist." 1 Not as numerically convenient as the Celsius scale and its theoretically-grounded successor Kelvin, the Réaumur scale never managed to gain the momentum of tradition that kept the Fahrenheit scale alive. It remains today as a historical curiosity, occasionally still used in parts of Eastern Europe.

The thermometer itself used alcohol mixed with water, rather than mercury, and often appeared as a component of a larger weather instrument such as a barometer. During the 18th and early 19th centuries CE Reaumur thermometers were in popular use; now they're mostly obsolete and tend to seriously confuse people when one shows up for sale at an auction or flea market.

Now odd and quaint, this device was once cutting-edge technology. Thomas Jefferson had one and kept records of using it regularly.2


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