The wacky Fahrenheit scale, invented by Daniel Fahrenheit 300 years ago, was based on a scale concocted by Ole Rømer, an astronomer who was the first to show that light has at a finite speed. On the Romer scale a brine solution freezes at 0 and plain water boils at 60. Why Rømer didn't use the same substance for both measurements is a mystery. Fahrenheight divided Rømer's degrees by 4 to make the scale finer, so in his version the brine froze at 0, normal water at 30, and human body temp was 90. These numbers had to be adjusted later as more accurate thermometers were made.