Thermometry or temperature measurement is important to a wide range of activities, including manufacturing, scientific research, and medical practice. The accurate measurement of temperature was developed only recently.
- Temperature (like mass, length, time) is a chosen fundamental quantity. Therefore, arbitrarily chosen units (such as degrees Celsius, degrees Fahrenheit or Kelvin) are used to measure temperature.
- Temperature is measured quantitatively by constructing a thermometer which makes use of a physical property of matter that varies with temperature.
- A physical property that changes continuously with temperature can be used to measure temperature and is usually referred to as its thermometric property.
Galileo invented the first thermometer. In his instrument, the changing temperature of an inverted glass vessel produced the expansion or contraction of the air within it, which in turn changed the level of the liquid with which the vessel’s long, open-mouthed neck was partially filled. This general principle was perfected in succeeding years by experimenting with liquids such as mercury and by providing a scale to measure the expansion and contraction brought about in such liquids by rising and falling temperature.