What is a characteristic feature of the mercury barometer?

The mercury barometer is specifically designed to measure atmospheric pressure using mercury, which is a dense liquid. This device operates on the principle that atmospheric pressure can support a column of mercury in a glass tube. As the atmospheric pressure changes, it causes the height of the mercury column to rise or fall, allowing for the measurement of that pressure in millimeters or inches of mercury.

The other options do not accurately represent the function of a mercury barometer: it does not measure temperature, humidity, or altitude. Instead, it serves a singular purpose of providing insights into atmospheric pressure, which is crucial for weather forecasting and understanding weather patterns.