An aneroid barometer measures air pressure without using liquid. Amercury barometer measures air pressure using liquid mercury.Mercury barometer and aneroid barometer are two instruments used in the pressure measurements. These two objects use different working principles and mechanisms. The aneroid barometer and mercury barometer are two of the most important devices used in the pressure measurements. These two devices are important both practically and theoretically. In this article, we are going to discuss what aneroid barometer and mercury barometer are, their working principles, the applications of mercury barometer and aneroid barometer, their similarities, and finally the difference between mercury barometer and aneroid barometer.