a galileo thermometer or galilean thermometer is a thermometer that uses the density of liquids to measure temperature. the thermometer was invented by galileo galilei, who had noticed that the density of a liquid changes with temperature. the thermometer is made of a glass container, filled with a liquid. inside, there are other containers, usually with other liquids. when the temperature changes, so does the density of the "container" liquid. as a consequence, the smaller containers may fall to the floor, or rise to the surface.