Which instrument measures atmospheric pressure?

A barometer is the correct instrument for measuring atmospheric pressure. It functions by using the weight of the air and can provide essential information about weather conditions. Essentially, a barometer detects changes in air pressure, which is pivotal for meteorological predictions. When atmospheric pressure increases or decreases, it can indicate upcoming weather patterns, such as storms or clear skies.

The other instruments listed serve different purposes: a thermometer measures temperature, a hygrometer gauges humidity, and an anemometer assesses wind speed. While all these instruments provide valuable data regarding weather, only the barometer specifically focuses on atmospheric pressure, making it the appropriate choice for this question.