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A thermometer (from the Greek θερμός, thermos, meaning "hot" and μἐτρον, metron, "measure") is a device that measures temperature or temperature gradient using a variety of different principles.[1] A thermometer has two important elements: the temperature sensor (e.g. the bulb on a mercury-in-glass thermometer) in which some physical change occurs with temperature, plus some means of converting this physical change into a numerical value (e.g. the visible scale that is marked on a mercury-in-glass thermometer).

There are many types and many uses for thermometers.

Contents [hide]

1 Temperature

2 Development

3 Physical principles of thermometry

3.1 Thermometric materials

3.2 Constant volume thermometry

3.3 Radiometric thermometry

4 Primary and secondary thermometers

5 Calibration

6 Precision, accuracy, and reproducibility

7 Nanothermometry

8 Uses

9 Types of thermometer

10 See also

11 References

12 Further reading

13 External links


While an individual thermometer is able to measure degrees of hotness, the readings on two thermometers cannot be compared unless they conform to an agreed scale. There is today an absolute thermodynamic temperature scale. Internationally agreed temperature scales are designed to approximate this closely, based on fixed points and interpolating thermometers. The most recent official temperature scale is the International Temperature Scale of 1990. It extends from 0.65 K (−272.5 °C; −458.5 °F) to approximately 1,358 K (1,085 °C; 1,985 °F).


Various authors have credited the invention of the thermometer to Cornelis Drebbel, Robert Fludd, Galileo Galilei or Santorio Santorio. The thermometer was not a single invention, however, but a development.

Philo of Byzantium and Hero of Alexandria knew of the principle 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.[2] The expansion and contraction of the air caused the position of the water/air interface to move along the tube.

Such a mechanism 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, notably Galileo Galilei.[3] As a result, devices were shown to produce this effect reliably, and the term thermoscope was adopted because it reflected the changes in sensible heat (the concept of temperature was yet to arise).[3] The difference between a thermoscope and a thermometer is that the latter has a scale.[4] Though Galileo is often said to be the inventor


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