What instrument is used to measure wind speed and direction?

An anemometer is the instrument specifically designed to measure both wind speed and direction. It typically consists of rotating cups or blades that turn in the wind, allowing for the calculation of wind speed based on the rate of rotation. Additionally, some anemometers are equipped with mechanisms to also determine the wind's direction, providing comprehensive data on wind conditions.

In contrast, a barometer measures atmospheric pressure and is often used in weather forecasting, while a thermometer measures temperature. A hydrometer is used to measure the density or specific gravity of liquids. None of these instruments provide the necessary information about wind speed and direction, making the anemometer the clear choice for this function.