Fahrenheit was a bit of a tinkerer. He wanted a scale that was practical for everyday life, not just for science experiments. He set 0° as the coldest thing he could reliably make in his lab: a mixture of ice, water, and salt.
Then, he decided 100° would be roughly the temperature of the human body. Roughly being the key word—turns out it’s closer to 98.6°F, but hey, nobody’s perfect.
Between that freezing salt-water slurry and his warm armpit, he had a scale. On that journey, fresh water froze at exactly 32°. It wasn’t a magical law of the universe; it was just a convenient stopping point.
