Learn More About Temperature and Thermometers

Through his experiments, Galileo Galilei (1564-1642) established the principle that the density of a liquid changes with temperature. His Termometro Lento, or "slow thermometer", was made possible by the skill of 17th Century European glass blowers.

Replicas of Galileo's Termometro Lento today are sculptures in glass that recreate his discovery. The glass globes of varying weights descend one by one as the temperature rises, since the liquid in which they are suspended is less dense and is not able to support them. Then, as the temperature falls, they slowly begin to rise. The lowest of the floats congregated at the top of the cylinder indicates the current temperature.

Today, temperature can be read using instruments that use alcohol, mercury, or electronic circuitry for measurement.