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Functioning of the Galilei thermometer

liquids have a characteristic weight that changes with alterations in temperature. This physical property is the functioning principle of Galilei thermometers. Galilei was an Italian scientist and lived from 1564 to 1642. He held the chair for mathematics at universities in Pisa and Padua and discovered numerous laws of nature, such as the alteration in specific weight of liquids.

Liquids in glass tubes expand when the temperature rises and constrict when the temperature falls. The small glass balls with temperature pendant slightly change in volume when temperature changes occur.

Every little glass ball of the Galilei thermometer is weighted during the manufacturing process, so that it, considering the additional weight of the metal pendant it carries, will have the same specific weight as the liquid in the glass tube when the according temperature is reached. The little ball starts floating now. If the temperature continues rising, the liquid in the glass cylinder expands and cannot hold the weight of the glass ball anymore. It thus begins floating downward. If the temperature lowers, the liquids in the glass cylinder constricts and the glass ball begins rising again.

The difference between the glass balls of the Galilei thermometer lies in the weight of each ball only, the liquids in them are close to meaningless. The difference in weight is extremely small and amounts to only 2 thousandths of a gramme.

If the temperature rises, the glass balls start floating downward, one after another.
If the temperature falls, the balls begin rising, one after another.
The current temperature can be viewed on the lowest - on top floating - ball.