The history of the thermometer goes back to the ancient Greeks. It is not known exactly who invented a working thermometer, but the earliest record has Philo of Byzantium creating what was called a “thermoscope” back in the second century B.C.E. Similarly crude devices using the expansion of water due to temperature were used throughout the centuries. The prolific Renaissance inventor and artist Galileo Galilei (1564–1642) improved the air thermoscope in 1593. The thermoscope he created uses a different approach to measuring temperatures than the thermometer. Instead of containing a fluid, such as mercury, that is sensitive to changes in heat and cold, the thermoscope suspends several objects within a transparent tube. The objects are small glass spheres containing various amounts of liquid and gas and also attached to a piece of metal that is suspended from each one. These floats have varying levels of buoyancy, which could be finely adjusted further by changing the size of the piece of metal attached. Galileo understood that water’s density changed with temperature, and so the buoys (distinguished by the color of the dyed fluid inside them) would rise or fall within the tube accordingly. You could tell the temperature based on which buoys were floating and which ones had sunk to the bottom of the tube. In 1610, Galileo replaced the water in the tube with wine (alcohol). Galileo’s friend Santorio Santorio (1561–1636) adapted the thermometer to measure body temperature in his medical practice).