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Ten Things You Maybe Didn't Know About the Degree Delisle

1. It runs backwards

Yep, on the Delisle scale, the hotter it gets, the lower the number. Water boils at 0 °De, and the numbers get bigger as it gets colder. Totally upside-down compared to what you’re used to.

2. Invented by a French astronomer

Joseph-Nicolas Delisle came up with the scale in 1732. He was an astronomer who wanted to create a thermometer that could handle wide temperature ranges accurately—especially for scientific expeditions.

3. Originally based on mercury

Delisle’s thermometers used mercury and were calibrated based on how much the mercury contracted as it cooled. The full scale originally had 2400 degrees between boiling and absolute cold (which he never actually reached).

4. Water freezes at 150 °De

In its later adjusted form, water freezes at 150 °De and boils at 0 °De. That means cold temperatures have higher numbers, which definitely takes some mental gymnastics.

5. Used mostly in Russia

While it was invented in France, it gained more traction in Russia during the 18th and 19th centuries, especially for scientific work. It never really caught on in Western Europe.

6. You can still convert it

To convert Delisle to Celsius: °C = 100 − °De × 2⁄3. That’s right, it’s got a little math involved, but it’s still totally possible to make sense of if you’re into historical temperatures.

7. It’s a rare collector’s curiosity

Delisle thermometers are basically antiques now. If you see one, it’s probably in a museum or in a collector’s cabinet — and probably still confusing visitors.

8. Part of the temperature scale boom

The 1700s were wild for temperature scales — Delisle, Newton, Réaumur, Rømer, and Celsius were all tossing out ideas. Delisle’s stood out for how ambitious and backwards it was.

9. No longer used, but not forgotten

The Delisle scale has faded into history, but it's still taught in metrology classes and pops up in trivia nights. It’s a reminder of how science evolves (and sometimes simplifies).

10. It reflects early science quirks

The Delisle scale shows how experimental and regional early science was. Before global standards, it was every inventor for themselves, and that led to some truly wild systems like this one.