Thermometry is the science of temperature measurement; changes in temperature are produced by the flow of heat from one body to another.
Thermometers, whose invention is attributed to Galileo Galilei, often make use of the thermal expansion of a liquid such as mercury or alcohol contained in very narrow tube.

Thermal expansion was of interest to scholars in the mid-18th century; measurements of the specific heat capacities of various substances were conducted in the late 1700s and early 1800s. Fundamental contributions were made by French scientists Antoine Laurent Lavoisier (Paris, 1743 – 1794) and Pierre Simon Laplace (Beaumont-en-Auge, 1749 – Paris, 1827), who laid the basis of modern chemistry.

The most important development occurred in the 19th century, with the birth of thermodynamics. The French physicist Nicolas Léonard Sadi Carnot (Paris, 1796 – 1832) established the theoretical foundations of production cycles of mechanical work obtained through the exchange of heat between two ‘reservoirs’ with different temperatures.

The birth of technological applications of thermodynamic cycles, such as the locomotive and the internal combustion engine, constituted the basis of industrial development.