4A10.20 Galileo's Thermometer


The temperature dependence of fluid density as a thermometric property


Galileo's thermometer is a sealed liquid-filled glass cylinder containing sealed glass floats (in this case, labelled 18, 19, 20, 21, 22, 24 and 26 degrees C). The floats are adjusted in density so they sink at different temperatures. The current temperature is indicated by the the lowest marked temperature that is floating.



  • [1] Galileo's thermometer
  • [1] 4 liter beaker (approximately 24 cm high)
  • [1] Roll of paper towels
  • [1] Bucket of ice
  • [1] Ice scoop

Important Notes

  • The temperature tags are small and may not show up very well on a camera.
  • The thermometer is fragile. Handle with care.
  • The glass floats respond quickly when placed in cold water, but they respond slowly when removed from the water.


  1. Read the temperature of the room on the thermometer.
  2. Pour the water (but not the ice) into the beaker.
  3. Place the thermometer in the beaker of water.
  4. Read the temperature in the cold water.


Additional Resources



  • Don't attempt this at home!

Last revised

  • 2021


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