Fahrenheit, Gabriel Daniel

Fahrenheit, Gabriel Daniel (1686-1736): German, Physicist

Fahrenheit, who was born in Danzig on 14 May 1686, revolutionized the thermometer in 1714, when he first used mercury instead of spirits of wine. The decision to use mercury was the result of a series of experiments that Fahrenheit conducted after reading the works of G. Amontons. Fahrenheit also revolutionized the design of the thermometer by sealing the mercury sealed inside a tiny glass bulb with a long, thin, cylindrical neck. This design replaced the spherical thermometers that were in use at the time. Fahrenheit chose mercury because it expanded uniformly when exposed to temperatures from about minus 40 to plus 626 degrees. After discovering that the zero-degree mark of his thermometer corresponded to the temperature of freezing salt water, he fixed his freezing point at 32 ° to avoid negative measurements.

During his investigations, Fahrenheit also discovered some of the physical properties of water, such as the fact that the boiling point of water varies with changes in atmospheric pressure. He also discovered the phenomenon of supercooling water, which is the process of cooling water to below its normal freezing point without converting it to ice. Such discoveries led him to doubt the reliability of using freezing and boiling points of water as a basis for a temperature scale. Eventually, he instead settled on a temperature scale ranging from 0º to 212º, based on the temperatures of the human body and of a mixture of water, ice and salt. In 1717 he moved his points to 32º and 96º in order to avoid fractions. Fahrenheit’s temperature scale hence became the first to be precise enough to become a worldwide standard. After Fahrenheit’s death, scientists adopted the temperature of 212º as the boiling point of water, but shifted the scale slightly to accommodate the change in boiling point that takes place with decreased atmospheric pressure. Hence, the normal temperature for the human body was set at 98.6º.

A contemporary of Fahrenheit’s, the Swedish Astronomer Anders Celsius designed a simpler scale whose 0 corresponded to boiling water and whose 100 corresponded to freezing water. He later reversed the scale to appease widespread objection.

An immediate and lasting impact of the invention of the Fahrenheit and Celsius thermometers was the worldwide founding of regional and national weather services. Although the instruments were clumsy in the beginning, eighteenth-century physicians began to use the thermometer, as well. It was 1866 before the British physician Thomas Clifford Allbutt invented the small clinical thermometer that is still used.

Further Reading:

Kimberly A. McGrath, ed., World of Invention: History’s Most Significant Inventions and the People Behind Them, 1999

Sarah Tusa