The German instrument maker Gabriel Daniel Fahrenheit (1686-1736) made the first reliable thermometers. The temperature scale he originated is named after him.

Born in Danzig on May 14, 1686, Gabriel Fahrenheit was the son of a well-to-do merchant. He lost both parents on the same day, Aug. 14, 1701, and was thereafter apprenticed to a shopkeeper in Amsterdam. After completing a term of 4 years there, he turned to physics and became an instrument maker and glassblower. Although he lived in Amsterdam most of his life, he traveled widely and spent considerable time in England, where he became a member of the Royal Society.

Fahrenheit completed his first two thermometers by 1714. They contained alcohol and agreed exactly in readings. The scale which was to bear Fahrenheit's name had not yet been calibrated, and many different scales were tried before he settled on one. He soon decided to replace the alcohol with mercury and completed a series of investigations based on the work of G. Amontons, in which he determined the boiling point of water and other liquids and studied the expansion properties of mercury. These experiments led to the discovery that the boiling point of water varied with changes in atmospheric pressure. Fahrenheit also discovered the phenomenon of supercooling of water, that is, cooling water to below its normal freezing point without converting it to ice.

Taking all of these factors into consideration, Fahrenheit was led to doubt the reliability of the freezing and boiling points of water and finally settled on a temperature scale ranging from 0 to 212. In 1724, announcing his method of making thermometers in the Philosophical Transactions of the Royal Society, he wrote concerning his scale, " ... degree 48, which in my thermometers holds the middle place between the limit of the most intense cold obtainable artificially in a mixture of water, of ice, and of sal ammoniac or even of sea salt, and the limit of heat which is found in the blood of a healthy man." (It has been suggested that the 96-degree range was chosen simply for the convenience of that number when laying off the scale by halving spaces on the thermometer stem.) Thus, finding the temperatures of the human body and of his freezing mixture to be reliable parameters, he set 0 as the temperature of the mixture; 32 as the temperature of water and ice; and 212, a point selected by chance, as about the boiling point of water.

Fahrenheit's thermometers were highly esteemed. He used mercury successfully because of his technique for cleaning it, and he introduced the use of cylindrical bulbs instead of spherical ones. However, his detailed technique for making thermometers was not disclosed for some 18 years, since it was a trade secret. Among the other instruments which he devised were a constant-weight hydrometer of excellent design and a "thermobarometer" for estimating barometric pressure by determining the boiling point of water.

On Sept. 16, 1736, Fahrenheit died, unmarried, in the Netherlands, presumably in The Hague, where he was buried.

Further Reading

• Henry Lipson, The Great Experiments in Physics (1968), includes a chapter on heat with reference to Fahrenheit. For background and additional material on Fahrenheit see Florian Cajori, A History of Physics (1899; rev. ed. 1929); Max von Laue, History of Physics (1947; trans. 1950); and Allen L. King, Thermophysics (1962).