German physicist, engineer, and glassblower Daniel Gabriel Fahrenheit, best known for inventing the alcohol and mercury thermometers and for developing a temperature scale now named after him, was born on this day in 1686.
Born in Danzig in the Polish-Lithuanian Commonwealth in 1686 as the eldest of five sons born to a German Hanse merchant family, Fahrenheit lived most of his life in the Dutch Republic. Though he began training as a merchant in Amsterdam to follow his family trade, Fahrenheit soon abandoned that line of work for natural science, his true interest. In 1717 he settled in The Hague as a glassblower, making barometers, scientific instruments used in meteorology to measure atmospheric pressure; altimeters, instruments used to measure the altitude of an object; and thermometers, where he ultimately found his calling. The following year, in 1718, Fahrenheit began lecturing in chemistry in Amsterdam.
During his travels through Europe, Fahrenheit met Olaus Roemer, a Danish astronomer in Copenhagen. Utilizing wine, Roemer had invented an alcohol thermometer with two points: 60 degrees as the boiling point of water and 7.5 degrees as the melting point of ice. At the time, temperature scales were not standardized and each scientist invented his or her own scale.
Inspired by Roemer’s design and scale and inspired to introduce more standardization into the science, Fahrenheit went to work on his own. He determined his scale using three fixed points of temperature. The lowest was achieved by preparing a mixture of ice, water, and ammonium chloride, a type of salt, and allowing the thermometer to descend to its lowest point, which was 0 °F. The second point of reference was taken by plunging the thermometer in still water when ice was just beginning to form on its surface. This registered at 32 °F. The final calibration was taken by placing the thermometer under an arm or in a mouth. This was read at 96 °F. (The scale was later adjusted by measuring the boiling point of water and making the freezing-to-boiling interval exactly 180 degrees. Using that calculation, normal body temperature is today taken as 98.6 °F.)
Though others have also been credited with inventing the alcohol thermometer before him, Fahrenheit’s alcohol thermometer, invented in 1709, provided one of the earliest, most efficient, and most accurate and reliable measurements of temperature. His mercury thermometer, invented in 1714, consisted of mercury in a blown glass tube. The Fahrenheit scale was widely used in Europe until the eventual switch to the Celsius scale, named after Anders Celsius, in 1948.