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The Réaumur is a unit of temperature named for René Antoine Ferchault de Réaumur, who first proposed it in 1731. The freezing point of water is 0° Reaumur, the boiling point 80° Reaumur. Hence a degree Reaumur is 1.25 degrees Celsius or kelvin.

Réaumur's thermometer was constructed on the principle of taking the freezing-point of water as 0°, and graduating the tube into degrees each of which was one-thousandth of the volume contained by the bulb and tube up to the zero mark. It was the dilatability of the particular quality of alcohol employed which made the boiling point of water 80°; and mercurial thermometers the stems of which are graduated into eighty equal parts between the freezing- and boiling-points of water are not Réaumur thermometers in anything but name.

The Reaumur scale is still used in some parts of Europe, but today it is in most places of mainly historical significance.

Réaumur is also the name of a commune in the Vendée département, in France.\n