An anemometer is an instrument for measuring wind speed. The rotation type, which estimates wind speed from the rotation of cups mounted on a vertical shaft, is the most common of mechanical anemometers. The pressure-tube instrument utilizes the pitot-tube effect, while the sonic or acoustic anemometer depends on the velocity of sound in the wind. For laboratory work a hot-wire instrument is used: here air flow is estimated from the change in resistance it causes by cooling an electrically heated wire.
For more details, see the anemometer entry in the Encyclopedia of Alternative Energy and Sustainable Living.