Our colourful glass thermometer is based on Galileo's theory: in liquid, a body of fixed mass becomes less buoyant as the liquid temperature rises, and more buoyant as the temperature decreases—due to changes in liquid density. As the temperature changes, the multicoloured balls rise and fall within the liquid-filled thermostatic tube. The lowest sphere in the top group within the instrument indicates ambient temperature. Made of glass, measures 23cm tall with five temperature indicators.