Fahrenheit's odd numbers come from halving a thermometer six times over
Why does ice melt at 32 on the Fahrenheit scale? Daniel Fahrenheit wanted 64 steps between melting ice and body heat, set at 32 and 96, so he could mark his glass tubes simply by halving the gap six times. Later tidying pushed normal body temperature to the familiar 98.6.
Fahrenheit, who lived from 1686 to 1736, proposed his scale in 1724. He built on the work of the Danish astronomer Ole Rømer, whom he had met, as he explained in a letter to Herman Boerhaave. Rømer's scale put freezing brine at zero and boiling water at 60, with awkward fractions in between. Fahrenheit multiplied everything by four to clear the fractions and gain finer divisions, then adjusted the marks for ice and the human body to land on 32 and 96.
His zero came from a frigorific mixture of ice, water and ammonium chloride, which settles at a steady temperature by itself. The trouble was that he also allowed sea salt, which settles several degrees lower, so the point was hard to reproduce; he probably never realised the two differed. A German story claims instead that zero was the coldest winter reading in his home town of Danzig in 1708 and 1709, and the brine came later.
After Anders Celsius popularised freezing and boiling water as reference points, a Royal Society committee led by Henry Cavendish adopted them in 1776 and 1777. Fahrenheit's scale was nudged so that water froze at exactly 32 and boiled at exactly 212, 180 degrees apart. That small redefinition is what moved body temperature up from 96. The scales cross at −40, where Fahrenheit and Celsius read the same.
Fahrenheit ruled weather, industry and medicine across the English-speaking world until the 1960s, when Celsius displaced it almost everywhere except the United States. It survives there, in its associated Pacific states and in the Cayman Islands, and on nearly every Canadian oven. Some British tabloids still reach for it in heatwaves, since 94 °F sounds more dramatic than 34 °C.
Source: Fahrenheit
