TFA Dostmann liquid thermometer GALILEO GALILEI Thermometer Coloured Liquid thermometer based on the idea of Galileo Galilei (1564-1642). Galileo discovered that liquids change their density depending on the temperature. When the temperature rises, the density of the liquid in the thermometer decreases. The relatively heavier spheres lose buoyancy and sink. If, on the other hand, the room temperature drops again, the lighter spheres gain buoyancy and gradually rise. The difference in weight of the glass spheres is calculated (to the nearest hundredth of a gram) so that the lower of the upper floating spheres always shows the current temperature range.