To read a Galileo thermometer, look at the lowest hanging bubble in the middle of the tube—the one that is not entirely sunk, nor entirely floating at the top. This bubble is in equilibrium with the surrounding liquid, and its tag will tell the current temperature.
Art meets science in this colorful glass thermometer. In 1593, Italian physicist Galileo invented a thermometer based on the principles of relative density. Individually calibrated weights containing a mixture of ethanol and dye float in a sealed tube with de-aromatic oil where they rise and fall with the temperature and the resulting changes in liquid density.
A simple, fairly accurate thermometer, today it is mostly used as decoration. The Galileo thermometer consists of a sealed glass tube that is filled with water and several floating bubbles. The bubbles are glass spheres.