Convert Delisle to Reaumur easily.

Temperature conversion doesn't get much more historical than this. While most of us breeze between Celsius and Fahrenheit these days, the Delisle and Réaumur scales offer fascinating glimpses into 18th-century scientific thinking. Let's explore how to bridge these two antique measurement systems.

Unit definitions

What is a Delisle (°De)?

Joseph-Nicolas Delisle created this inverted scale in 1732 while working in Russia. Water boils at 0°De and freezes at 150°De, making it one of the few scales that decreases as temperature rises. It maintained popularity in Russia for nearly a century before metrication.

• Symbol: °De
• Common uses: Historical Russian meteorological records
• Definition: (100 - Celsius) × 1.5

What is a Reaumur (°Ré)?

French scientist René Antoine Ferchault de Réaumur proposed his scale in 1730, dividing the range between freezing and boiling water into 80 degrees. This made calculations simpler in pre-decimal Europe. Surprisingly, some European cheesemakers still reference Réaumur in traditional production methods.

• Symbol: °Ré
• Common uses: Historic European science, food production
• Definition: Celsius × 0.8

Conversion formula

The direct conversion between these scales eliminates Celsius:
Réaumur = 80 - (Delisle × 0.8)

Example calculations

1. Converting 100°De to Réaumur:
   80 - (100 × 0.8) = 0°Ré
2. Converting 50°De to Réaumur:
   80 - (50 × 0.8) = 40°Ré

Conversion tables

Delisle to Reaumur

Reaumur to Delisle

From observatories to cheese caves

The Delisle scale's story begins in St. Petersburg's imperial observatory, where Joseph Delisle needed precise instruments for astronomical calculations. His mercury thermometer design accidentally created a temperature scale that outlived its original purpose. Meanwhile, Réaumur's work with thermal expansion in liquids led to his eponymous scale that became standard in Enlightenment-era laboratories.

Both scales faced obsolescence as metrication spread, but their legacy persists. Modern historians analyzing 18th century Russian weather records must convert Delisle measurements, while European artisan cheese producers still monitor aging caves using Réaumur thermometers for tradition's sake.

Interesting facts

1. Delisle's original scale had 2,400 degrees between boiling and freezing, later simplified to 150°
2. Russia's Academy of Sciences used Delisle exclusively until 1740
3. Réaumur's scale influenced Linnaeus' development of Celsius
4. Some Swiss alpine cheeses specify aging temperatures in Réaumur
5. The coldest theoretical temperature (-273.15°C) equals 559.725°De

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