4A10.20 • Galilean Thermometer

Location: Cabinet 10

Photo and Video Shows the Demonstration Used at U.T. Austin

Concepts Conveyed:

• The Galilean thermometer measures temperature using colorful floating capsules of different fixed effective densities submerged in ethanol inside a closed glass tube.
• The depth of the floating capsules is determined by the density of the surrounding ethanol solution.
• When the densities of the capsule and the environment are equal, the capsule is stationary.
• The density of ethanol is sensitive to changes in temperature. For instance, when the ethanol is heated (using the hot water), the density of the solution gradually decreases, causing more capsules to sink to the bottom.
• The temperature of the solution is indicated by the lowest number on the still-floating capsules.

Demo Staff Notes:

• Add enough water to a pot to fill it approximately 75% of the way up.
• Put the pot of water on a hotplate, and heat until it is hot, but not boiling. START THIS PROCESS AT LEAST 30 MINUTES BEFORE ROLLING OUT DEMO!
• Pour water into the thermos to keep warm for the class.
• Provide a short, wide beaker in which the base of the Galilean thermometer can be submerged.

Last updated on April 27, 2026