Daniel Gabriel Fahrenheit

Daniel Gabriel Fahrenheit was born in 1686 in Danzig (now Gdańsk), then part of the Polish–Lithuanian Commonwealth, into a merchant family of German descent. Orphaned at fifteen when both parents died from eating poisonous mushrooms, he was apprenticed to a merchant in Amsterdam, but his fascination with scientific instruments drew him away from commerce and into the trade of glassblowing and instrument making, in which he became the finest practitioner of his age.

Fahrenheit's central achievement, around 1714, was the first reliable mercury-in-glass thermometer. Mercury expands more uniformly than the alcohol used by earlier makers and remains liquid over a wide range, and Fahrenheit's skill in producing fine, even bores made his instruments reproducible — two of his thermometers would agree, something no earlier maker could guarantee. This reproducibility, more than any single invention, made quantitative thermometry possible.

He fixed his scale to reproducible points: zero at the temperature of a freezing brine of ice, water, and ammonium chloride, and a higher mark near human body temperature. On the resulting scale water freezes at 32° and boils at 212°, a span of 180 degrees. The fine resolution of the Fahrenheit scale made it popular for meteorology and it remains in everyday use in the United States.

Fahrenheit also studied the supercooling of water, the dependence of boiling point on pressure, and the densities of liquids with a hydrometer of his own design. Elected to the Royal Society in 1724, he spent most of his career in the Dutch Republic and died in The Hague in 1736.