The Galileo Thermometer works on principles developed by Galileo Galilei (1564-1642), the pioneer of modern astronomy and physics. Through his experiments, Galileo discovered that liquids change density as the temperature increases or decreases.
How it Works
A glass sphere is filled with clear liquid. Floating inside the sphere are two small glass bulbs. The bulbs are calibrated by filling them with precise amounts of colored liquid so that they have a specific density relative to the clear liquid in the main tube (some bulbs are calibrated to be higher in density and some are lower). Finally, metal tags that serve as counter weights are hung from each bulb. A temperature is engraved on each tag.
When temperature rises, the liquid inside the glass thermometer tube becomes less dense and the liquid-filled bulbs will sink. When the temperature drops, the liquid inside the tube becomes denser and the liquid-filled bulbs will float. Since the bulbs are different density, some will sink or float more than others.