Which instrument is used to measure atmospheric pressure?

The instrument used to measure atmospheric pressure is the barometer. Barometers function based on the principle that changes in external pressure cause changes in a liquid column, typically mercury or water, within the device. As atmospheric pressure increases, it pushes down on the liquid, causing it to rise in the tube, while a decrease in pressure allows the liquid to fall. Hence, the height of the liquid column is indicative of the surrounding air pressure.

This measurement is crucial for meteorology, as it helps in weather prediction and understanding atmospheric conditions. High-pressure systems often correlate with clear skies, while low-pressure systems can indicate stormy weather. Other instruments, like a thermometer, measure temperature; an altimeter is designed to measure altitude by assessing atmospheric pressure, and an anemometer measures wind speed, but none of these serve the specific purpose of measuring atmospheric pressure.