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  • >> DEREK: How did Celsius define his scale?

  • >> MICHAEL: Uh... He took the temperature water freezes at and said that's zero and then he took the

  • temperature it boils at and says that's a hundred. And he figured a hundred

  • was a good amount of demarcations to make in between the two. Right?

  • >> DEREK: Yeah. Except that's not what he did. >> MICHAEL: Really?

  • >> DEREK: Celsius never devised nor used the scale that now bears his name.

  • >> MICHAEL: Are you kidding me? >> DEREK: No, Michael, I'm not!

  • This is the Swedish town of Uppsala, located 70 kilometers north of Stockholm.

  • So this is the house where Celsius lived. In 1741 he was professor of astronomy at

  • Uppsala University. And this is the first ever Celsius thermometer... or is it?

  • >> This is the first scale of Anders Celsius added onto... or, added onto an old

  • thermometer.

  • So we have Delisle' scale on the left hand side and Celsius' new scale in the right.

  • >> DEREK: These few markings show that Celsius came up with

  • the idea of separating the freezing and boiling points of water by 100 degrees.

  • He made his first observations with the scale on Christmas Day 1741. But have you

  • noticed something strange about this scale?

  • I mean, 50 is marked in the middle but the numbers increase down towards the

  • bulb of the thermometer. So, Celsius had his scale upside down.

  • He set zero degrees at the boiling point of water and a hundred at the

  • freezing point.

  • Why would he do this? Well, for one thing

  • Celsius was just following the convention of the other scale on the

  • thermometer. Delisle' scale also had zero degrees for the boiling point of

  • water increasing down to 150 for his freezing point. And a likely reason both

  • of them used upside down scales is because they avoid negative numbers.

  • In Sweden it gets much colder than freezing but never warmer than boiling water so

  • you don't have to worry about pesky minus signs and this helps avoid logbook

  • errors.

  • I think it would be really weird if you had water boiling

  • zero degrees and freezing at a hundred. Wouldn't that be strange?

  • Although it might seem strange today, there is no objectively good reason for

  • preferring an ascending scale over a descending one for measuring degrees of

  • something, like hot or cold.

  • In fact, when Celsius died of tuberculosis in 1744, he was still using

  • this inverted scale.

  • So who reversed it? Who do we have to thank for the modern Celsius temperature scale?

  • Well in 1745, just a year after Celsius' death

  • a new column appears in the Uppsala temperature record using the modern

  • scale and at the top it's got the heading "Ekström" Now Ekström was the

  • instrument maker at Uppsala. In 1747 another column is added with the heading

  • Strömer who was Celsius' successor as professor of astronomy.

  • Again, it's got the same modern scale. But it's another professor at Uppsala who

  • claims that he reversed the scale:

  • That's the famous biologist Carl Linnaeus. He says he reversed the scale

  • when he ordered a thermometer from Ekström for his greenhouse.

  • Whoever it was, we know that by 1745 there was an operational thermometer at

  • Uppsala University with a scale that we now all know as the Celsius temperature scale.

  • Except... this was not the first such thermometer ever created. In 1743 the

  • year before Celsius died, a French scientist working independently in Lyon

  • created a thermometer with zero degrees at the freezing point of water and a

  • hundred at the boiling point.

  • his name was Jeane Pierre Christin. So why isn't it called a degree Christin instead

  • of a degrees Celsius?

  • Well, for a long time this temperature scale wasn't referred to using either of

  • their names and instead it was just called the "centigrade scale," meaning a

  • hundred steps.

  • The problem with this was "centigrade" has other meanings in French, Spanish and

  • Italian, where a grade specifically refers to one one-hundredth of a right

  • angle. So to eliminate this confusion the International Bureau of Weights and

  • Measures in 1948 decided to rename the centigrade scale after a scientist

  • bringing it into alignment with other temperature scales like Kelvin

  • and Fahrenheit. They chose Celsius possibly due to a popular 1800's German

  • chemistry textbook by a guy named Berzelius. In it, Berzelius identified

  • Celsius as the first to devise a temperature scale with zero at water's

  • freezing point and a hundred at its boiling point propagating the myth that

  • Celsius created this scale. So is Celsius undeserving of having his name

  • immortalized on weather maps around the world?

  • Well, no. I mean making two marks and deciding on a number of degrees in

  • between them that is the easy part which others could, and as history shows, did do...

  • but what Celsius did was he established which physical processes could reliably

  • produce a fixed temperature. At the time when he was working, there were some 30

  • different temperature scales in use. Some thermometers had 18 different scales on

  • them, some more reliable than others. For fixed reference points one scale used the

  • deepest cellar of the Paris observatory,

  • others used the melting temperature of butter, the internal temperatures of

  • certain animals, or the hottest day in summer in Italy, Syria or Senegal. These

  • dubious scales combined, with inconsistent thermometer construction

  • made recording accurate temperatures nearly impossible, not to mention sharing

  • those temperatures with other scientists elsewhere. Celsius solved this problem in

  • a number of ways: he demonstrated that melting snow maintains a fixed temperature

  • regardless of latitude or ambient pressure. He also determined the precise

  • relationship between boiling point of water and the ambient pressure, so that

  • thermometers could be calibrated under any conditions.

  • He made it possible to establish a universal reliable system of temperature

  • measurement and this is why Celsius' name is a unit of temperature, even

  • though the scale itself was not created by him and in fact today the Celsius

  • scale is no longer defined by either of water's phase transition points, instead

  • it is based off the Kelvin scale and that scale is defined by setting the

  • triple point of water,

  • where solid, liquid, and gas all exist in equilibrium at exactly 273.16 Kelvin.

  • This fixes the size of a degree Kelvin, which is exactly the same as the size of

  • a degree Celsius. The zero point of the Celsius scale is set a 273.15 Kelvin.

  • And what all this means is that today pure water boils at

  • 99.974 degrees Celsius and freezes at negative

  • 0.0001 Celsius. This precision in a nearly universal system of temperature

  • measurement is thanks to a huge number of scientists

  • so the C after the degree symbol stands not only for Celsius or Christin

  • or Carl Linnaeus, but for the community of scientists whose work over centuries

  • made a scale so robust that we take it for granted.

  • [sound effects]

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>> DEREK: How did Celsius define his scale?

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Celsius Didn't Invent Celsius

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    林宜悉 posted on 2020/03/28
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