A Galileo thermometer is a temperature measuring device invented by Galileo Galilei in the 16th century. It consists of a sealed glass cylinder filled with a liquid, such as water or alcohol, and several glass bulbs of different densities suspended inside the liquid. Each bulb contains a metal tag indicating the temperature at which it will sink to the bottom of the cylinder.
To read a Galileo thermometer, simply observe which bulb is floating at the bottom of the cylinder. The temperature indicated on the tag of that bulb is the current temperature. Galileo thermometers are relatively accurate and can measure temperatures ranging from about -10 to +50 degrees Celsius.
