History of the Thermometer

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Air and water expand and contract with a change in temperature. Around 1600, scientists who understood that concept began experimenting with other materials to see if they would expand and contract too. That is the basic premise behind a thermometer. By using materials that change in some way when they are heated and cooled, a thermometer measures temperature. Modern thermometers are calibrated in standard temperature units such as Fahrenheit and Celsius. But before we discuss that, let's first look at the early history of thermometers.

Early history

The first thermometers were called thermoscopes. A thermoscope measures temperature by using a column of air in a tube with one end of the tube immersed in a container of colored water. Galileo Galilei invented a rudimentary water thermometer in 1593 which, for the first time, allowed temperature variations to be measured. In 1610 Galileo tried it with wine instead, and so is credited with the first alcohol thermometer. The first sealed thermometer was designed in 1641 for the grand duke of Tuscany.

The modern thermometer

In 1714, a German instrument maker, Gabriel Fahrenheit settled on mercury as the most suitable liquid for measuring temperature. He calibrated his first thermometer by using a mixture of ice and water with sea salt. But salt water has a much lower freezing point than ordinary water, so he chose 30 as the freezing point for his thermometer and 96 as the healthy temperature inside a human's mouth. He established the boiling point of water at 212 and later adjusted the freezing point of water on his thermometer to 32. That way, he could count exactly 180 degrees between boiling and freezing. In 1724 he introduced the scale that bears his name, the Fahrenheit Scale. Mercury thermometers are still widely used.

The celsius ccale

Some scientists thought 180 was an awkward number to work with and began working to change it. Two decades later the Swedish astronomer, Anders Celsius, worked out a scale of just one hundred degrees between freezing and boiling points. Because there were 100 steps between the two points, it was called a centigrade scale. Many modern thermometers use the Celsius Scale.

In 1948, an international conference of weights and measure adopted the Celsius Scale as the standard measure, but old habits die hard. Fahrenheit is still used widely in Britain and the U.S.

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