How it works: The thermometer employs the principle of buoyancy and density. The body is mostly filled with paraffin, and any remaining air is removed from the tube. This allows the paraffin to expand and contract as needed, and isolates it from air pressure, which can affect the density of liquids. For most fluids, as temperature increases the density decrease – water is a notable exception which is why the Galileo Thermometer uses paraffin, as it responds to changes in temperature more quickly than water. As the temperature of the paraffin falls and it becomes denser, the baubles will rise. Each bauble is carefully weighted so that they will swap from floating ti sinking at a particular temperature, giving you a reading. How to use it: If there is a bauble floating in the middle of the thermometer, the attached tag will read the current temperature. If the middle of the thermometer is empty, then the temperature is on degree les than the lowest floating ball. If all the baubles are floating, then the temperature is at or below the minimum reading. Likewise, if all the baubles have sunk, the temperature is at or above the highest possible reading.