What the Fahrenheit?!

As an Australian Canadian, the Fahrenheit temperature scale has always seemed a bit arbitrary to me. I mean, why does water freeze at 32 degrees? Why that integer? And what exactly does 0 represent? According to many sources, the Fahrenheit scale was defined by setting 0 degrees equal to the temperature of the ice, salt, and water mixture, and a hundred degrees being roughly equal to human body temperature. But that isn't true. The real story is much more interesting and scientific.

August 14th, 1701, was almost certainly the worst day in the life of 15-year-old Daniel Gabriel Fahrenheit. On that day, both of his parents died suddenly from mushroom poisoning. And he was sent from Poland, where he lived, to Amsterdam to become an apprentice bookkeeper. But Fahrenheit couldn't stand his apprenticeship and ran away so many times that his employer put out a warrant for his arrest.

Traveling from city to city around Europe, he became fascinated with scientific instruments and, in particular, thermometers. In 1708, possibly seeking help with the warrant, Fahrenheit met with the mayor of Copenhagen, who happened to be the famous astronomer Ole Rømer. Rømer is known for observing the eclipses of Jupiter's moons and realizing that variations in the timing of those eclipses were caused by the time it took light to reach Earth. In other words, he found a way to accurately measure the finite speed of light.

But, more pertinent to this story, in 1702, Rømer was housebound after breaking his leg. To pass the time, he devised a brand-new temperature scale with the freezing point of water at 7.5 degrees and body temperature at 22.5 degrees. Now, this might seem odd until you consider that Rømer wanted the boiling point of water to be 60 degrees. As an astronomer, he had experience dividing things by 60.

So, if you take this scale, divide it in half, in half again and in half once more, you find the freezing point of water one eighth up the scale, and human body temperature three eighths up the scale. So at their meeting in 1708, Fahrenheit learned of Rømer's temperature scale and adopted it as his own, adjusting it slightly because he found it "inconvenient and inelegant on account of fractional numbers."

So, he scaled them up to 8 and 24. And this is the original Fahrenheit scale. He produced thermometers for some time using this scale. But then, at some later point, Fahrenheit multiplied all numbers on the scale by 4, setting the freezing point to the now-familiar 32 and body temperature to 96. It's unclear exactly why he did this. He may just have wanted finer precision in his measurements.

But I think there was a better reason. You see, Fahrenheit was an excellent instrument maker. His thermometers agreed with each other precisely at a time when that was unheard of. He pioneered the use of mercury as a measuring liquid, which has the benefit of a much higher boiling point than the alcohol used in most other thermometers at the time. And for these accomplishments, he was inducted into the British Royal Society.

And we know that he read the works of Newton, Boyle, and Hook, in which he would have come across the idea that one degree increase in temperature could correspond to a specific fractional increase in the volume of the measuring liquid. And today, a one degree Fahrenheit increase in temperature increases the volume of mercury by exactly one part in 10,000. Is this just a coincidence? Well, we'll probably never know for sure, because as an instrument maker, Fahrenheit was very secretive about his methods.

But I think the data strongly suggest that this was the case. So, what exactly did zero represent on the scales of Fahrenheit and Rømer? By many accounts, it's the temperature of a salt, ice, and water mixture. The only problem is there are different descriptions of these mixtures, and none of them actually produces the temperature they're supposed to. More likely, I think they picked the coldest temperature in winter, set that as zero, and later used ice and brine to calibrate new thermometers.

In his day, the Fahrenheit thermometer was the best you could get. But now, his scale is only used regularly in the Cayman Islands, Bahamas, Belize—oh, and the United States of America. So maybe it's time we all adopted the global scale of temperature: Celsius, which, by the way, wasn't invented by Celsius at all.

Hey! So that was something a little bit different. This video was animated by Marcello Ascani. I've got a link to his channel in the description. You know, I became really fascinated with the temperature scale after I saw the original Celsius thermometer. You can see that video here.

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And I have a book that I would recommend to you. It is called "The Structure of Scientific Revolutions" by Thomas S. Kuhn. This is a classic in the history and philosophy of science. And it'll make you see science in a different way because it shows us that science is not just one process; but there are actually revolutions that take place when big discoveries are made. And that really changed my thinking about science when I first read this book ten years ago.

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