How Gabriel Fahrenheit used his wife's mouth to set his thermometer

Time to grapple with the mail that drops into our “Say What?” bin. The “Matthew, You Fraud” stuff. The most immediately eye grabbing is an extended e from one Alex Censor, edited here because, well, because nobody can stop me.

You got a detail wrong on your explanation of how Gabriel Fahrenheit set the 100-degree mark on his thermometer (“The top of his scale was average humanan body temperature. He called that 96.”). Doesn't it strike you as odd that a scientist would say, “Hmmm, I think 96 is a nice number for human body temperature”? [Actually], for the story to work he'd have had to make an evert weirder decision, "Hmmm, I think 98.6 is a nice number.” According to my physiology teacher in my doctorate program at the University of Illinois, a rather meticulous British fellow who never would propagate a falsehood, here's how it happened.

[Fahrenheit] decided to use human body temperature for the 100-degree mark. He put the thermometer in [his wife's] mouth arid scratched a mark on the glass at her body temperature and called that 100 degrees. [But] his wife was running a slight fever. By the time he and the world discovered that most folks were a tiny bit cooler [98.6], it was too late to change his scale.

Great story, Alex. But untrue in detail and spirit, I believe. Fahrenheit wasn’t trained as a scientist. He went to business school but became a designer of ingenious measuring instruments. When he happened on a nifty glass-tube thermometer invented by a Danish astronomer, he adapted the device by replacing the alcohol in the tube with mercury and reworking its very peculiar temperature-measuring scale (low marker: 7.5 degrees, the melting point of ice; high marker: 60 degrees, the boiling point of water). As he stated in one of his letters, Mr. F didn’t like “inconvenient and awkward fractions,” so he divided each degree in the Danish scale into four Fahrenheit degrees and set as his zero-degree point the temp of a mixture of ice, water, and salt. Since he already had a calibration, he simply measured stuff to set other benchmarks. The freezing point of water clocked in at 32 Fahrenheit degrees. And, as he wrote, his third benchmark was normal human body temperature, “when the thermometer is held in the mouth or under the armpit of a living man in good health.” On his already established scale, that happened to be 96 degrees. The feverish Mrs. F may have donated her pits to the cause, but she didn’t make scientific history in the process.

Basically, Fahrenheit cared about fixing a zero-degree point, and after that he let the thermal chips fall where they may. After Fahrenheit’s death, scientists re-calibrated his scale slightly, and human body temp then became 98.6. Revised Fahrenheit is the scale we use now. So, with all due respect to your learned prof, ka-BLOOEY! The sound of an anecdote self-destructing.