What Is a Barometer Air Pressure Measurement, Types & Meteorology
A barometer is a scientific instrument designed to measure atmospheric pressure—the downward force exerted per unit area by the weight of the column of air in Earth’s atmosphere above a given location. Because air possesses mass, gravity pulls atmospheric gases downward toward the Earth's surface, generating atmospheric pressure that varies with altitude, air temperature, and dynamic meteorological weather patterns. Measuring these subtle pressure variations provides meteorologists with one of the most reliable tools for predicting weather changes, tracking cyclonic storms, and calculating aviation altitudes.
The mercury barometer was invented in 1643 by the Italian physicist and mathematician Evangelista Torricelli, a student of Galileo Galilei. In his groundbreaking experiment, Torricelli filled a one-meter glass tube sealed at one end with liquid mercury and inverted it into an open reservoir of mercury. Instead of emptying completely, the mercury column settled at a height of approximately 760 millimeters (29.92 inches) above the basin level, leaving an empty space at the top of the tube termed the "Torricellian Vacuum." The mercury column remained suspended because the downward weight of mercury inside the tube was exactly balanced by the downward atmospheric pressure pushing on the surface of the mercury in the open reservoir. Mercury was selected because its high density (13.6 g/cm3) allows for a compact, manageable column; a water barometer would require a glass tube over 10.3 meters tall.
In 1844, French inventor Lucien Vidi developed the Aneroid Barometer, which measures atmospheric pressure without using liquid. It utilizes a sealed, flexible metal capsule (an aneroid capsule) crafted from copper-beryllium alloy that is partially evacuated of air. As external atmospheric pressure increases, the thin corrugated walls of the capsule are compressed inward; when pressure drops, an internal spring expands the capsule. This mechanical movement is magnified through levers to turn a needle across a calibrated dial. In meteorology, rising barometric pressure indicates approaching high-pressure anticyclones with clear, dry weather, whereas a rapid drop in barometric pressure warns of incoming low-pressure storm systems, rain, and gales.