anemometer An instrument for measuring the speed of wind, or any other flowing fluid. In a simple vane anemometer, a number of caps or vanes are fixed on a spindle. The moving air causes the spindle to rotate. The speed of rotation is calibrated to give the wind speed. A hot wire anemometer consists of a resistor which is heated electrically. When kept in flowing wind its temperature falls, which causes its resistance to change. The change in resistance is measured. From this the velocity of the fluid is found.