Which instrument measures the atmospheric pressure?

The instrument that measures atmospheric pressure is the barometer. Barometers work on the principle of balancing the weight of a column of mercury (or other liquid) against the atmospheric pressure. When atmospheric pressure increases, it pushes the mercury up the tube, indicating higher pressure, and when it decreases, the mercury level falls. This measurement is crucial for weather forecasting and understanding atmospheric conditions since changes in atmospheric pressure are often associated with different weather patterns.

The other instruments listed serve different purposes: thermometers measure temperature, anemometers measure wind speed, and hydrometers measure the specific gravity of liquids. Each of these instruments is essential in meteorological observation, but only the barometer directly provides data on atmospheric pressure. Understanding how each instrument functions helps meteorologists gather comprehensive weather data for analysis.