Instrument particularly suited to the measurement of very low air velocities and the fluctuating velocities that occur in turbulent flow. Basically, it consists of a wire or wires, usually platinum, supported in a frame and heated electrically. When exposed to an air current, the heated wire cools, and as a result, its electrical resistance alters. The heated wire forms one arm of a Wheatstone-bridge-type circuit, and measurements of resistance change may be correlated with the velocity of airflow that caused that change.