What instrument measures wind speed?

An anemometer is the instrument specifically designed to measure wind speed. It typically consists of rotating cups or blades that catch the wind, with the speed of rotation correlating to the speed of the wind. This allows meteorologists and researchers to quantify how fast the wind is blowing, which is crucial for weather forecasting, aviation, and many other applications.

The other instruments serve different purposes: a barometer measures atmospheric pressure, a hydrometer measures the specific gravity of liquids, and a thermometer measures temperature. Each of these plays an important role in meteorology and other fields, but none of them is intended for measuring wind speed, which highlights the unique function of the anemometer in weather observation and analysis.