An aneroid barometer is used to measure atmospheric pressure without using liquid. It consists of a sealed, flexible metal chamber that expands or contracts with changes in atmospheric pressure. In this demonstration, a large open aneroid barometer is displayed, showing how the metal chamber inside reacts to changes in pressure. By blowing into or sucking on the chamber, you can visibly observe the expansion and contraction of the barometer, which provides a direct and tangible illustration of how pressure variations affect the device. This demonstrates the principle behind aneroid barometers and their use in weather forecasting and altimetry.