In existographies, Daniel Fahrenheit (1686-1736) (Gottlieb 1000:261) (CR:10) was a Polish-born German physicist noted for his circa 1720 invention of the mercury thermometer.

Overview

In c.1724, Fahrenheit, influenced by Guillaume Amontons' 1699 constant volume air thermometer work and finding that water boils at constant temperature, made a mercury thermometer.

In prior alcohol thermometers, the variability in alcohol’s purity made it difficult to obtain reproducible results; the use of mercury by Fahrenheit solved this issue. [1]

In a letter to his associate Herman Boerhaave, eponym of Boerhaave’s law, Fahrenheit acknowledged that he got his idea for his thermometer from Danish astronomer Ole Romer (who had invented his own thermometer in 1701), albeit using a renumbered scale, in which he used the fixed points of 96 (instead of 22.5 or 90), the temperature of his wife's armpit, 32 the temperature of ice melting in water), and 0 the temperature of a bath of ice melting in a solution of common salt; a scale that he says he began using in 1717. [2] In the letter, Fahrenheit is said to have commented: “as this graduation is inconvenient and awkward because of the fractions, I decided to alter the scale, and to use 96 instead of 22½ or 90; this I have always used since then.” [3]

The Fahrenheit scale (˚F), along with the improved Celsius scale (˚C), made by Anders Celsius in 1742, and eventual universal thermodynamics-based Kelvin scale (˚K), made by William Thomson in 1848, is one of the main indicators with which to measure temperature.

Education
Fahrenheit was orphaned in 1701, at the age of 16, when both his parents died of mushroom poisoning. He then was sent by his new guardians to Holland to apprentice at a bookkeeping firm, which he eventually ran away from. He then travelled about from city to city, studying under the likes of Gottfried Leibniz and Herman Boerhaave, among others.

Photo | Note
No extant photos of Fahrenheit exist; the one shown, above right, is a 2012 computer-generated image (Ѻ) based on images of his relatives.

Quotes | By
The following are quotes by Fahrenheit:

“I read that the celebrated Amontons, using a thermometer of his own invention, had discovered that water boils at a fixed degree of heat. I was at once inflamed with a great desire to make for myself a thermometer of the same sort, so that I might with my own eyes perceive this beautiful phenomenon of nature.”
— Daniel Fahrenheit (1724), “Experiments and Observations Concerning the Congealment of Water in a Vacuum” [4]

References
1. Blumberg, Mark S. (2002). Body Heat: Temperature and Life on Earth (pgs. 18-17). Harvard University Press.
2. Romer scale – Wikipedia.
3. (a) Ernst Cohen discovered in a Leningrad archive a letter in Dutch from Fahrenheit to Herman Boerhaave.
(b) Cohen, Ernst and Cohen-De Meester, W.A.T. (1936). “article”, Chemisch Weekblad, Vol. 33: 374-93.
(c) Middleton, W.E. Knowles. (1966). A History of the Thermometer and its Use in Meteorology (pg. 71). Johns Hopkins Press.
4. Fahrenheit, D.G. (1724). “Experiments and Observations Concerning the Congealment of Water in a Vacuum” (“Experimenta et Observationes de Congelatione aquae in vacuo factae a D. G. Fahrenheit” (Ѻ), Philosophical Transactions, London, Vol. 33, pg. 78.

Further reading
● Fahrenheit, Daniel. (1724). “Experiments on the Degree of Heat in Boiling Liquids”, Philosophical Transactions of the Royal Society (pg. 1).
● Bolton, Henry Carrington (1900). Evolution of the Thermometer, 1592-1743 (section: "Fahrenheit and the First Reliable Thermometers", pgs. 61-79). The Chemical Publishing Company.

External links
● Daniel Fahrenheit – Wikipedia.