Science Of...

The Celsius Thermometer Is Upside Down

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On its face, the Celsius temperature scale seems like an obvious discovery: find the freezing point of water and make that zero, then find the boiling point of water and make that 100. But that's not actually how it was devised. Celsius's thermometer was a revision of one designed by Delisle, which had 0 degrees set at the boiling point of water, not the freezing point. Celsius had recently published his discovery that the freezing point of water was independent of latitude—a contested issue in scientific circles at the time—and, in 1742, he was able to design his thermometer with the freezing point of water at 100 degrees. Though it might seem backward to flip the thermometer from what we know today, these demarcations actually made a lot of sense. In Celsius's country of Sweden, temperatures often exceeded freezing but never went past boiling. This flipped scale helped scientists avoid negative numbers, since negative signs on paper are easily overlooked, leading to errors. Though the exact point that Celsius's scale was flipped to the modern one is unclear, most attribute it to Celsius's university colleague Carl Linnaeus. He's said to have first used it in 1745, a year after Celsius's death. We've collected some awesome videos on this topic. Watch them now to learn more.


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Key Facts In This Video

  1. Celsius had his scale upside down from the scale we use today, as did his predecessor. That's to avoid negative numbers. 01:15

  2. Its origins are unclear, but we do know that by 1745, there was a thermometer at Upsala University with the Celsius scale we know today. 02:27

  3. Celsius was the first to establish which physical processes could reliably produce a fixed temperature. Past scales had used wildly unreliable standards. 04:28