While searching for a method for measuring temperature, physicist Galileo Galilei (1564-1642), discovered that the density of a liquid changes as a function of temperature. In order to make his experiments reproducible, he took 4-5 glass balls, filled them with different amounts of water, sealed them and now had a clue for the temperature of his liquid.
The hand-blown balls of the thermometer are precisely weighed and given an indicator mark. This has to be done with great precision because there is a difference in weight of only a few thousandths of a gram between two consecutive balls. This guarantees a high accuracy of the temperature display of ± 1 ° C.
If the temperature rises, the balls fall down very slowly and if they drop again, the balls rise very slowly. The current temperature is read from the seal on the lowest of the balls floating above. The production of the Galilean glass ball thermometer is complex and almost entirely handcrafted.