Fahrenheit? Celsius?

A Straight Dope Classic from Cecil's Storehouse of Human Knowledge
December 15, 1989

Dear Cecil:

Everybody knows 0 degrees on the Celsius scale is the freezing point of water and 100 degrees is the boiling point. On the Fahrenheit scale, however, freezing is 32 degrees and boiling 212. How on earth were these numbers arrived at? Do 0 and 100 degrees Fahrenheit mean anything?

— Leslie, Montreal, Quebec

Cecil replies:

Researchers have gone to their graves trying to figure out what old man Fahrenheit was up to, Leslie. Here's the story as well as I can piece it together:

Daniel Gabriel Fahrenheit (1686-1736) was a German instrument maker who invented the first practical mercury thermometer. Casting about for a suitable scale for his device, he visited the Danish astronomer Ole Romer, who had devised a system of his own. As it turned out, it was a case of the blind leading the blind.