Thermometers

All thermometers of conventional design are descended from a device invented by the Italian scientist Galileo in 1592, and now known as a thermoscope. It was a narrow glass tube with a bulb at the bottom. This was filled with water, and the top was left open. If the temperature of the surroundings rose the water would expand, causing its level in the tube to rise. The amount of expansion was tiny, but the change in level was amplified by the fact that the bulb was much larger in diameter than the tube.