Summer has given way to Fall -- and Fall seems to be courting Winter altogether too well this morning. It's 36°F out there right now. And this is none of your scientific, 100-steps-from-froze-to-boiling stuff, either, but good old two-fisted Fahrenheit, established with buckets of slushy brine and the feverish body temperatures of Daniel Gabriel Fahrenheit and his wife, which is how come we ended up with 98.6 as the normal body temperature.
Or so the story goes. The truth is a little more complicated: 0°F was supposed to be the temperature that water, ice and ammonium chloride stabilize at, 30°F the freezing point of water and 90°F the normal human temperature. But that's sixty divisions from frozen to you, not all that easy to rule by eye. Fahrenheit was working in the 1720s, a time when precision work was very much a do-it-yourself process, and it's simplest to use a power of two for that: you can keep on dividing down using, well, dividers, a process that can yield surprising accuracy in skilled hands. 64 divisions work out, putting water's freezing point at 32, body temperature at 96 (and there, probably, are our feverish Fahrenheits -- but not so fast) and, conveniently, the boiling point of water right around 212°F
Time wore on, and not very much time, either, before scientific dignity and convenience looked for a better way to define that high end than lining up a few select friends and sticking thermometers in their mouths. Boiling water was a lot easier to come by and, as long as you hung out at sea level, a nice, stable reference that wasn't going to catch a cold and throw the whole process out of whack. In 1776, Henry Cavendish of England's Royal Society proposed setting exactly 212°F at the boiling point of water, and there we were. There's no telling what Fahrenheit might have thought of it; after a busy career of science, instrument-making, teaching and invention, he died in 1736 at the age of 50.
Physicians, meanwhile, were still stuck using our normal temperature as a reference point. If you're like me, you grew up being told it was 98.6°F (and Cavendish had doctors and nurses sqinting to examine thermometer scales for the decimal). But possibly medical science was still in the fever-swamps of measurement when they picked that; these days, 98.2°F seems to be the standard for oral temperature, and there's a wide band of acceptable temperatures.
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