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WATCH: Why People Still Use This Crazily Arbitrary Temperature Scale

What even is zero degrees Fahrenheit?

FIONA MACDONALD
2 DEC 2016
 

While the vast majority of the world now measures temperature in degrees Celsius, the US (as well as three small island nations) still use the Fahrenheit scale. 

But despite the loyalty to this system, not many people actually know how it came about. For instance, why does water freeze at the arbitrary figure of 32 degrees Fahrenheit? And what exactly does zero degrees Fahrenheit represent?

 

Many sources (including Wikipedia) will tell you that the Fahrenheit scale was defined by setting zero degrees equal to the temperature of an ice, salt, and water mixture, and 100 degrees is roughly equal to human body temperature.

That makes sense, but as the latest episode of Veritasium explains, it's not actually true. The real story is a lot stranger, and a lot more scientific.

It all starts back on 14 August 1701, when 15-year-old Daniel Gabriel Fahrenheit was having a terrible day. Both his parents had died suddenly from mushroom poisoning, and he was sent from his hometown in Poland to Amsterdam to become an apprentice book keeper.

The only problem was that Fahrenheit hated his apprenticeship, and ran away so many times, his employer put out a warrant for his arrest.

So Fahrenheit spent the next several years as a fugitive, hopping from European country to European country, all while studying and developing a fascination for scientific instruments - specifically, the thermometer.

 

During that time, Fahrenheit met with the mayor of Copenhagen, who just so happened to be the famous astronomer Ole Rømer. It turns out that, back in 1702, Rømer had broken his leg, and to pass the time, had come up with a brand new temperature scale.

Rømer's temperature scale was based on the boiling point of water being 60 degrees - astronomers are used to dividing things by 60, seeing as space is divided up this way into arcminutes and seconds.

And according to Rømer's new scale, the freezing point of water was 7.5 degrees, and human body temperature 22.5 degrees.

When Rømer told the thermometer-obsessed Fahrenheit about this new scale, Fahrenheit decided it was a good way to measure temperature, and decided to take it as his own. He adjusted it slightly to round the freezing point of water up to 8, and human body temperature up to 24.

And that is the original Fahrenheit scale.

Fahrenheit started making thermometers using this scale for several years, but at some point, he multiplied all numbers on the scale by four, making freezing point the now familiar 32, and human body temperature 96.

It's still not entirely clear why he did this. Fahrenheit was notoriously secretive when it came to making his instruments, which were by far the most precise at the time - he was the one who pioneered the use of highly accurate mercury in his thermometers.

But Derek from Veritasium thinks it might have had something to do with his being inducted into the British Royal Society, where he was exposed to the works of Newton, Boyle, and Hooke.

After reading about their researcher, he would have come across the idea that a 1-degree increase in temperature could correspond to a specific fractional increase in the volume of the measuring liquid. 

So what does that have to do with anything? Well, as random as the Fahrenheit scale might seem to those who aren't familiar with it, Derek notes that, today, a 1-degree-Fahrenheit increase in temperature increases the volume of mercury by exactly 1 part in 10 thousand.

Knowing all that, what does zero represent on the scales of Fahrenheit and Rømer? Well, we'll let Derek explain that one in the video above, but one thing's for sure, it's not the temperature of a random combination of ice, salt, and water.

The real question now is: should we still be using such an arbitrary temperature scale when Celsius is a much simpler scale?

We'll let you guys discuss that among yourselves, but we have to admit we're team Celsius all the way on this one.

Oh, and in case you were wondering, the Celsius temperature scale wasn't actually invented by Celsius at all (see the video below). Because the history of temperature measurements just happen to be much stranger than fiction.

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