The scientific instrument that measures atmospheric pressure is called a barometer. Barometers can be categorized mainly into two types: mercury barometers and aneroid barometers. Mercury barometers utilize a column of mercury in a glass tube, while aneroid barometers use a sealed, flexible metal box. Changes in atmospheric pressure are crucial for predicting weather patterns and determining altitudes. Accurate measurements are vital for meteorology, aviation, and other scientific fields that rely on understanding atmospheric conditions and how they impact the environment.