__NOTOC__ The Réaumur scale (; °Ré, °Re, °r), also known as the "octogesimal division", is a

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

scale for which the

melting Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which in ...

and

boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding env ...

s of

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

are defined as 0 and 80 degrees respectively. The scale is named for

René Antoine Ferchault de Réaumur René Antoine Ferchault de Réaumur (; 28 February 1683, La Rochelle – 17 October 1757, Saint-Julien-du-Terroux) was a French entomologist and writer who contributed to many different fields, especially the study of insects. He introduced t ...

, who first proposed a similar scale in 1730.

Change in scale

Réaumur's

thermometer A thermometer is a device that measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a mercury-in-glass thermometer ...

contained diluted

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

(ethanol) and was constructed on the principle of using 0° for the melting temperature of water, 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. He suggested that the concentration of alcohol employed be such that it began boiling at 80 °Ré – that is, when it had expanded in volume by 8%. He chose alcohol instead of mercury because it expands more visibly, but this posed problems: his original thermometers were very bulky, and the low boiling point of alcohol made them unsuitable for many applications. Instrument-makers generally chose different liquids, and then used 80 °Ré to signify the boiling point of water, causing much confusion. During 1772 Jean-André Deluc studied the several substances then used in thermometers and concluded that mercury thermometers were the best for practical use; for example, if two equal amounts of water at ''x'' and ''y'' degrees were mixed, the temperature of the result was then the average of ''x'' and ''y'' degrees, and this relationship was only reliable when mercury was used. From the late 18th century mercury was used almost without exception. Its range is 0 to 80 degrees.

Use

The Réaumur scale was used widely in Europe, particularly in France, Germany and Russia, and was referenced in the works of

Thomas Mann Paul Thomas Mann ( , ; ; 6 June 1875 – 12 August 1955) was a German novelist, short story writer, social critic, philanthropist, essayist, and the 1929 Nobel Prize in Literature laureate. His highly symbolic and ironic epic novels and novell ...

Dostoyevsky Fyodor Mikhailovich Dostoevsky (, ; rus, Фёдор Михайлович Достоевский, Fyódor Mikháylovich Dostoyévskiy, p=ˈfʲɵdər mʲɪˈxajləvʲɪdʑ dəstɐˈjefskʲɪj, a=ru-Dostoevsky.ogg, links=yes; 11 November 18219 ...

, Flaubert,

Tolstoy Count Lev Nikolayevich TolstoyTolstoy pronounced his first name as , which corresponds to the romanization ''Lyov''. () (; russian: link=no, Лев Николаевич Толстой,In Tolstoy's day, his name was written as in pre-refor ...

, and

Nabokov Vladimir Vladimirovich Nabokov (russian: link=no, Владимир Владимирович Набоков ; 2 July 1977), also known by the pen name Vladimir Sirin (), was a Russian-American novelist, poet, translator, and entomologist. Born ...

. For example, at the beginning of Book X of ''

The Brothers Karamazov ''The Brothers Karamazov'' (russian: Братья Карамазовы, ''Brat'ya Karamazovy'', ), also translated as ''The Karamazov Brothers'', is the last novel by Russian author Fyodor Dostoevsky. Dostoevsky spent nearly two years writing '' ...

'', the narrator says, "We had eleven degrees of frost", i.e. −11 °Ré, equivalent to −14 °C or 7 °F. By the 1790s, France had chosen the

Celsius The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The d ...

scale as part of the

metric system The metric system is a system of measurement that succeeded the decimalised system based on the metre that had been introduced in France in the 1790s. The historical development of these systems culminated in the definition of the Intern ...

, rather than the Réaumur measurement, but it was used commonly in some parts of Europe until at least the mid-19th century, and in parts of Russia until the early 20th. While living in Paris, George Orwell mentions "translating Réaumur into Fahrenheit" even in 1929. Its main modern uses are in some Italian and Swiss factories for measuring milk temperature during cheese production,Reaumur thermometer for Parmigiano-Reggiano cheese)
/ref> and in the Netherlands for measuring temperature when cooking sugar syrup for desserts and sweets.

Conversion between different temperature units

Notes and references

{{DEFAULTSORT:Reaumur Scale Obsolete units of measurement Scales of temperature Science and technology in France Scales in meteorology