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Galileo Thermometer

Infinity candle

Galileo's thermometer works on the principle that the density of a liquid changes as its temperature changes...

The Galileo thermometer is named after Galileo Galilei, who did not build such a thermometer but discovered the principle on which such a thermometer works. This thermometer consists of a sealed glass cylinder containing a clear liquid. If the air surrounding the thermometer is warmer, the liquid in the thermometer is also warm, and its density is lower. However, if the air around the thermometer is cooler, the density of the liquid is higher. Inside the clear liquid are small vessels containing different colored liquids. These small vessels rise or fall according to the temperature of the liquid, which is surrounding them. Whether a particular vessel rises to the surface, floats, or sinks depends on the weight attached to it. Higher temperature labels have less weight, and lower temperature labels have more weight. We determine the temperature using a label on a weight that is currently floating in the middle of the thermometer. In this case, the total density of the small container and the weight attached to it is equal to the density of the liquid surrounding it.


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