The scientific instrument used to measure atmospheric pressure is called a barometer. Barometers are essential tools in meteorology and are used to predict weather changes. There are several types of barometers, with the mercury barometer and aneroid barometer being the most common. A mercury barometer uses a column of mercury in a tube, where changes in atmospheric pressure cause the mercury level to rise or fall, indicating the pressure. An aneroid barometer, on the other hand, uses a sealed, flexible metal chamber that expands or contracts with pressure changes. These instruments help provide valuable data for weather forecasting and scientific research.