History of the Thermometer

Daniel Fahrenheit - Fahrenheit Scale

Ice covered thermometer, close-up
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What can be considered the first modern thermometer, the mercury thermometer with a standardized scale, was invented by Daniel Gabriel Fahrenheit in 1714.

History

Various people are credited with inventing of the thermometer including Galileo Galilei, Cornelis Drebbel, Robert Fludd and Santorio Santorio. The thermometer was not a single invention, however, but a process. Philo of Byzantium (280 BC–220 BC) and Hero of Alexandria (10–70 AD) discovered that certain substances, notably air, expand and contract, and described a demonstration in which a closed tube partially filled with air had its end in a container of water.

The expansion and contraction of the air caused the position of the water/air interface to move along the tube.

This was later used to show the hotness and coldness of the air with a tube in which the water level is controlled by the expansion and contraction of the gas. These devices were developed by several European scientists in the 16th and 17th centuries, and eventually were called thermoscopes. The difference between a  thermoscope and a thermometer is that the latter has a scale. Though Galileo is often said to be the inventor of the thermometer, what he produced were thermoscopes.

Daniel Fahrenheit

Daniel Gabriel Fahrenheit was born in 1686 in Germany into a family of German merchants, however, he lived most of his life in the Dutch Republic. Daniel Fahrenheit married Concordia Schumann, daughter of a well-known business family.

Fahrenheit began training as a merchant in Amsterdam after his parents died on August 14, 1701, from eating poisonous mushrooms.

However, Fahrenheit had a strong interest in natural science and was fascinated by new inventions such as the thermometer. In 1717, Fahrenheit became a glassblower, making barometers, altimeters, and thermometers. From 1718 onwards, he was a lecturer in chemistry. During a visit to England in 1724, he was elected a Fellow of the Royal Society.

Daniel Fahrenheit died in The Hague and was buried there at the Cloister Church.

Fahrenheit Scale

The Fahrenheit scale divided the freezing and boiling points of water into 180 degrees. 32°F was the freezing pint of water and 212°F was the boiling point of water. 0°F was based on the temperature of an equal mixture of water, ice, and salt. Daniel Fahrenheit based his temperature scale on the temperature of the human body. Originally, the human body temperature was 100° F on the Fahrenheit scale, but it has since been adjusted to 98.6°F.

Inspiration for the Mercury Thermometer

Fahrenheit met Olaus Roemer, a Danish astronomer, in Copenhagen. Roemer had invented an alcohol (wine) thermometer. Roemer's thermometer had two points, 60 degrees as the temperature of boiling water and 7 1/2 degrees as the temperature of melting ice. At that time, temperature scales were not standardized and everybody made up their own scale.

Fahrenheit modified Roemer's design and scale, and invented the new mercury themometer with a Fahrenheit scale.

The first physician that put thermometer measurements to clinical practice was Herman Boerhaave (1668–1738). In 1866, Sir Thomas Clifford Allbutt invented a clinical thermometer that produced a body temperature reading in five minutes as opposed to 20.