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| Réaumur scale | |
|---|---|
| Name | René Antoine Ferchault de Réaumur |
| Birth date | 1683 |
| Death date | 1757 |
| Nationality | French |
| Known for | Réaumur temperature scale |
Réaumur scale The Réaumur scale is a historical temperature scale devised in the early 18th century by French scientist René Antoine Ferchault de Réaumur. It played a role alongside contemporary developments by Anders Celsius, Daniel Gabriel Fahrenheit, and Lord Kelvin in shaping thermometry used across Europe and in scientific instrumentation during the Enlightenment and Industrial Revolution. The scale influenced practical practices in fields associated with figures and institutions such as François-Marie Arouet de Voltaire, the Académie des Sciences, the Jardin du Roi, the Royal Society, and the Prussian Academy of Sciences.
Réaumur proposed his scale in 1731 while corresponding with members of the Académie des Sciences and exhibiting work at salons attended by Antoine Lavoisier, Jean-Jacques Rousseau, Georges-Louis Leclerc, Comte de Buffon, and contemporaries in Paris. The scale spread through networks connected to the French Navy, House of Bourbon administrative reforms, and printing centers in Paris, Amsterdam, and Berlin. It was adopted in artisan communities influenced by guilds in Lyon, Rouen, and Milan and featured in manuals produced by instrument makers associated with workshops near Guildhall and Gewerbehalle institutions. During the 18th and 19th centuries, proponents in the courts of Frederick the Great, commissioners at the Imperial Russian Academy of Sciences, and scientists at the University of Göttingen debated Réaumur versus Celsius scale and Fahrenheit scale standards. The scale’s adoption intersected with industrial patrons such as the Watt steam engine manufacturers and textile merchants in Manchester and Lodz.
Réaumur defined his scale with zero at the freezing point of a particular aqueous mixture and 80 degrees at the boiling point of water under local atmospheric pressure. Réaumur’s reference relied on methods practiced at the Royal Observatory, Greenwich, the Paris Observatory, and experimental protocols discussed at the Royal Institution and the École Polytechnique. The choice of an 80-degree interval connected to duodecimal and centesimal traditions found in discussions among members of the Philosophical Transactions readership, pamphleteers in Leipzig, and instrument treatises circulated by publishers in Venice and Geneva.
A Réaumur degree was defined by Réaumur to be one eightieth of the interval between two reproducible fixed points, a concept refined by instrument makers like those working for the Habsburg courts and technicians trained at the Technische Hochschule. Calibration practices were influenced by standards developed at the Bureau International des Poids et Mesures precursor discussions and comparative studies conducted in laboratories at Cambridge University, Oxford University, and the University of Paris (Sorbonne). Craftsmen in Nuremberg, Florence, Turin, and Antwerp produced thermometers with alcohol or mercury columns scaled in degrees Réaumur for patrons such as the Medici and industrialists like Matthew Boulton.
The Réaumur scale was widely used in confectionery and distillation texts from authors connected with the Académie des Sciences de Lyon, in brewing manuals for brewers in Munich and Brussels, and in textile dyeing recipes employed in workshops in Ghent and Bordeaux. Adoption persisted in agricultural treatises endorsed by agronomists linked to estates of Louis XV and in viticulture guides circulated among vintners near Bordeaux, Burgundy, and Piedmont. Municipal public works in cities such as Milan and Zurich referenced Réaumur in descriptions of snowmelt and ice formation used by engineers influenced by the writings of Gottfried Wilhelm Leibniz and administrators trained under the Napoleonic Code. Technical journals published in St. Petersburg and Vienna recorded comparative measurements in Réaumur alongside Reaumur-period Celsius and Fahrenheit readings.
Conversion formulas between Réaumur, Celsius, Fahrenheit, and Kelvin were established in comparative studies undertaken at institutions including the Royal Society, the Académie des Sciences, and the Prussian Academy of Sciences. The linear relationships permitted transformations such as multiplying Réaumur degrees by 1.25 to obtain Celsius values, a technique applied in engineering calculations by firms like Boulton and Watt and standardized in metrology circles connected to the International Committee for Weights and Measures. Thermodynamic work by scientists affiliated with the University of Göttingen and the École des Mines de Paris employed conversions when reporting experimental temperatures in multilingual publications.
Thermometers graduated in Réaumur were produced by prominent instrument makers whose workshops maintained clientele among the House of Habsburg, the House of Savoy, and urban municipal governments in Hamburg and Lille. Designs ranged from alcohol-filled glass capillary thermometers used in domestic kitchens of Naples and Seville to mercury thermometers for laboratory use at the Collège de France and apparatus in the laboratories of Joseph Priestley and Henry Cavendish. Barometers, psychrometers, and calorimeters of the period often presented temperatures in Réaumur in treatises published by houses in Leiden and Strasbourg.
By the late 19th and early 20th centuries, the Réaumur scale declined in favor of the Celsius and Kelvin standards promoted by international metrology bodies and national academies such as the British Association for the Advancement of Science, the Deutsche Physikalische Gesellschaft, and the Académie des Sciences. The scale remained in use in particular trades in Alsace, Lorraine, and parts of Italy into the interwar period, with collectors and historians at museums like the Science Museum, London, the Musée des Arts et Métiers, and the Deutsches Museum preserving specimens. Réaumur’s influence persists through historical thermometry scholarship at institutions such as Sorbonne University, Utrecht University, and the Max Planck Society, and through archival collections in libraries at Bibliothèque nationale de France and the Bodleian Library.