Convert Wedgwood to Delisle like an 18th-century scientist

Ever wondered how porcelain makers measured kiln temperatures before modern thermometers? Or how Russian scientists recorded freezing winters in the 1700s? The Wedgwood and Delisle temperature scales tell this story. While you'll never use these units in a modern lab, understanding them is like holding a thermometer to history itself.

Unit definitions

What is a Wedgwood (°W)?

Josiah Wedgwood (yes, the pottery magnate) created this scale in 1782 to control clay firing temperatures. Its zero point corresponds to 1077.5°C, with each °W representing approximately 130°C. Potters loved its practical approach: they'd measure how much a clay sample shrank when heated to determine temperatures. Though innovative for its time, it couldn't measure below 1077.5°C, making it useless for everyday weather.

Symbol: °W
Key fact: 1°W ≈ 130°C increase

What is a Delisle (°De)?

Joseph-Nicolas Delisle developed his inverted scale in 1732 for astronomical observations. In a quirky twist, water boils at 0°De and freezes at 150°De. Russia adopted it for nearly a century, with Daniel Fahrenheit even contributing to its development. The scale's backward nature (temperatures decrease as heat increases) confuses modern users but made sense for recording sub-zero St. Petersburg winters.

Symbol: °De
Key fact: 1°De = -2/3°C

Conversion formula

The mathematical bridge between these antiquated scales is: °De = 1766.25 - (195 × °W)

This formula combines two conversions: first from Wedgwood to Celsius (°C = °W × 130 - 1077.5), then to Delisle (°De = (100 - °C) × 1.5). The simplified version above skips the intermediate Celsius step.

Example calculations

1. Converting 8°W to Delisle: 1766.25 - (195 × 8) = 1766.25 - 1560 = 206.25°De
2. A pottery kiln at 12°W equals: 1766.25 - (195 × 12) = 1766.25 - 2340 = -573.75°De

Wait, negative Delisle? That's normal! Remember, Delisle's scale continues below water's boiling point. This result suggests an extremely high temperature (≈1482.5°C) that would make even experienced potters sweat.

Conversion tables

Wedgwood to Delisle

Delisle to Wedgwood

From clay kilns to frozen observatories

The Wedgwood scale's creation was driven by industrial necessity. Josiah Wedgwood needed consistent results in his pottery business, and existing mercury thermometers couldn't withstand kiln temperatures. His solution? Measure how much clay samples contracted at specific heats. While innovative, the scale had limitations. A 1792 Royal Society paper noted its margin of error (±7°C) made precise scientific work challenging.

Delisle's story begins in Paris but found its true home in Russia. When the French astronomer brought his scale to St. Petersburg in 1725, local scientists appreciated its granularity for extreme cold. At its peak, 30°De (-20°C) was considered a mild winter day. The scale's persistence in Russia until 1826 demonstrates how measurement systems can become cultural fixtures, even when better options exist.

Fun fact: Both scales benefit from modern conversion tools. In their heyday, converting between them required complex logarithmic tables and manual calculations that could take hours.

Five temperature tales you'll want to share

1. Wedgwood's secret sauce
   The original Wedgwood pyrometer used small clay cylinders. Artisans would fire them alongside pottery, then measure shrinkage with a special microscope.
2. Delisle's scale flip
   The original Delisle scale had water boiling at 0°De and freezing at 150°De. Later users reversed it, creating confusion in historical records.
3. Fahrenheit's cameo
   Gabriel Fahrenheit helped Delisle calibrate his thermometers, creating a brief overlap between the two measurement systems.
4. The pottery preservation paradox
   Museums now use Wedgwood conversions to authenticate 18th-century ceramics. Glaze colors reveal original firing temperatures.
5. Russia's century-long chill
   When Russia finally switched to Celsius in 1826, meteorologists had to reinterpret 100 years of Delisle-based weather records.

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