Convert Réaumur to Delisle like an 18th-century scholar.

Ever wondered how scientists in 1700s Europe measured temperature without modern tools? They used scales like Réaumur and Delisle, two systems that feel almost poetic in their complexity. While you probably won’t need these for baking cookies, they offer a fascinating glimpse into the history of science. Let’s explore how to bridge these two relics with a converter that’s faster than you can say "thermometric evolution."

Unit definitions

What is a réaumur (°ré)?

The Réaumur scale, named after French scientist René Antoine Ferchault de Réaumur, sets water’s freezing point at 0°Ré and boiling point at 80°Ré. It was widely used in Europe during the 18th and 19th centuries, particularly in France, Germany, and Russia. Cheesemakers still occasionally reference it for aging processes. Symbol: °Ré. Definition: 1°Ré = 1.25°C.

What is a delisle (°de)?

Created by French astronomer Joseph-Nicolas Delisle in 1732, this scale does everything backward. Water boils at 0°De and freezes at 150°De, with values increasing as temperatures drop. It’s like the contrarian cousin of temperature scales. Symbol: °De. Definition: 1°De = -2/3°C.

Conversion formula

To convert Réaumur to Delisle:
Delisle = (80 - Réaumur) × 1.25

Why? Since both scales relate to Celsius but invert each other, you’re essentially flipping Réaumur’s 80-degree range into Delisle’s 150-degree spread. Multiply by 1.25 to scale it up properly.

Example calculations

1. Converting 16°Ré to Delisle
   (80 - 16) = 64
   64 × 1.25 = 80°De
2. Converting 40°Ré to Delisle
   (80 - 40) = 40
   40 × 1.25 = 50°De

Funny enough, 80°Ré (boiling water) equals 0°De, while 0°Ré (freezing) becomes 100°De. It’s a perfect mirror image with a mathematical twist.

Conversion tables

Réaumur to Delisle

Delisle to Réaumur

From wine cellars to observatories: A brief history

Réaumur developed his scale in 1730 while studying the expansion of liquids, initially using alcohol instead of mercury. His work became a benefit to European industry, particularly in metallurgy and food preservation. Delisle, on the other hand, was mapping Siberian winters when he devised his scale. Ironically, Russia adopted his system more enthusiastically than his homeland France. By the mid 1800s, both scales began fading as Celsius and Fahrenheit gained dominance, though you will still find Réaumur references in Swiss alpine weather stations and vintage French cookbooks.

Interesting facts

1. Upside-down universe: A hot summer day (30°C) equals 24°Ré but -45°De. The lower the Delisle number, the warmer it is!
2. Cheese legacy: Traditional Swiss Gruyère production still uses Réaumur for monitoring fermentation temperatures.
3. Astronomical roots: Delisle created his scale specifically for calibrating thermometers in Saint Petersburg’s observatory.
4. Scale showdown: In 1740, Swedish botanist Carl Linnaeus compared Réaumur and Delisle thermometers side-by-side, calling the latter "a numerical labyrinth."
5. Survival story: The Delisle scale remained Russia’s official standard until 1927, long after most countries switched to Celsius.

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