Hi Lynn,

No one really knows how Farenheit defined his scale. There are several competing theories, including the idea that 0°F is the temperature he measured at which a mixture of salt and water froze (something to do with the coldest winter where he lived (in Poland)).

But I'm willing to bet that the story you're thinking of is the one wherein 0°F is the temperature at which a person would (hypothetically) freeze to death and 100°F is the temperature at which a person would (again hypothetically) die from heat exhaustion. Of course, since I don't know of any reference to anything resembling an LD50 and Farenheit, and since I have personally worked in greater than 100°F temperatures (as a longshoreman in the hold of a ship in August in Southwest Louisiana) without dying of heat exhaustion, I tend to be suspicious of this version of the story.