Look closely at each metal medallion. You will see a temperature engraved onto it. Different Galileo thermometers have different ranges of temperatures that they can report. For example, many have a range of 60 °F (16 °C) to 100 °F (38 °C) and won’t tell you the temperature if it’s higher or lower than those values.
The spheres also contain liquid, but it changes density much less rapidly than the clear liquid in the thermometer, so it isn’t affected by the temperature change. The spheres are different colors just to look beautiful.
Keep in mind that Galileo thermometers are not super precise. They’ll be able to tell you roughly the temperature of the room, within 4 °F (−16 °C). Their main benefit is that they’re beautiful, with all those floating glass spheres.
Using a beaker of water is great for a classroom demonstration because the temperature change between the air and the water makes for a dramatic show.
This is the most common scenario.
For example, if one sphere says 72 and one says 68, your average temperature would be 70.
The spheres float because the liquid inside the tube becomes denser than the spheres.
The spheres sink in high temperatures because as the liquid in the tube heats up, it becomes less dense than the spheres.
