Convert Romer to Delisle easily.

Ever wondered how people measured temperature before Celsius and Fahrenheit took over? Let’s talk about two historical scales, Romer and Delisle, and how to convert between them. If you’re restoring old European scientific texts or just love quirky measurement systems, this guide is your trusty sidekick.

Unit definitions

What is a Romer (°Rø)?

The Romer scale was invented in 1701 by Danish astronomer Ole Rømer. It’s one of the earliest temperature scales that used fixed reference points. Water freezes at 7.5°Rø and boils at 60°Rø under standard atmospheric pressure. Fun fact, Daniel Gabriel Fahrenheit visited Rømer and later based his own scale on this system.

Symbol: °Rø
Common uses: 18th-century Danish thermometers, pre-industrial science
Definition: 0°Rø = freezing point of brine, 60°Rø = boiling water

What is a Delisle (°De)?

Created in 1732 by French astronomer Joseph-Nicolas Delisle, this scale flips the script. Unlike most systems, Delisle temperatures decrease as heat increases. Water boils at 0°De and freezes at 150°De. Russia adopted it for over a century because its inverted scale avoided negative numbers during harsh winters.

Symbol: °De
Common uses: 18th-century Russian meteorology
Definition: 0°De = boiling water, 150°De = freezing water

Conversion formula

To convert Romer to Delisle, use this equation:
°De = (60 − °Rø) × 20⁄7

Let’s break it down. Subtract the Romer value from 60 to align with Delisle’s inverted scale, then multiply by 20/7 to stretch the interval between freezing and boiling points. The 20/7 ratio comes from dividing Delisle’s 150-degree freezing range by Romer’s 52.5-degree range (60 − 7.5).

Example calculations

Example 1: Convert 25°Rø to Delisle
(60 − 25) = 35
35 × 20⁄7 = 100°De

Example 2: Convert 10°Rø to Delisle
(60 − 10) = 50
50 × 20⁄7 ≈ 142.86°De

Conversion tables

Romer to Delisle (common values)

Delisle to Romer (common values)

Historical background and cultural impact

Ole Rømers scale was groundbreaking because it introduced fixed calibration points, a concept later refined by Fahrenheit. But why did Delisle invert his scale? Joseph-Nicolas Delisle worked in Russia, where winters were brutally cold. His system started at boiling water (0°De) and increased as temperatures dropped, which meant thermometers rarely showed negative numbers in snowy Saint Petersburg. Talk about practical design.

Russia used the Delisle scale until the 19th century, when Celsius became the continental standard. Meanwhile, Rømer’s design faded after Fahrenheit improved upon it by adjusting the reference points for greater precision. Today, both scales survive mainly in historical records and niche scientific discussions.

Interesting facts

1. Double Legacy: Delisle’s scale was modified twice. The original version had water freeze at 2,400°De, but his student Josias Weitbrecht recalibrated it to the 150°De range we know today.
2. Fahrenheit’s Inspiration: Fahrenheit attended one of Rømer’s lectures and later tweaked his scale by multiplying Rømer’s intervals by 4. This led to the 32°F freezing point we still use.
3. Thermometer Wars: In the 18th century, instrument makers competed to build the most accurate Delisle thermometers, often engraving them with elaborate floral patterns.
4. Coldest Recorded Delisle: The lowest temperature ever measured in Delisle was −358.3°De at Antarctica’s Vostok Station in 1983. That’s equivalent to −89.2°C.
5. Modern Niche: Some vintage clockmakers still use Delisle thermometers to monitor workshop conditions , claiming they’re easier to read in cold environments.

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