Ambient Weather Galileo Thermometer and Glass Globe Fluid Barometer The Galileo thermometer consists of a sealed glass tube that is filled with liquid and several floating bubbles. The bubbles are glass spheres filled with a colored liquid mixture. Attached to each bubble is a little metal tag that indicates a temperature. The bubbles are calibrated by adding a certain amount of fluid to them so that they have the exact same density. So, after the weighted tags are attached to the bubbles. As the temperature of the air outside the thermometer changes, so does the temperature of the liquid surrounding the bubbles. As the temperature of the liquid changes, it either expands or contracts, thereby changing its density. The concept that 'decreasing atmospheric pressure predicts stormy weather' was postulated by Lucien Vidie -- and it's the basis for a weather prediction device called a storm glass or liquid barometer. A narrow spout connects to the body below the liquid level and rises above the liquid level, where it is open to the atmosphere.