Leonardo da Vinci designed an anemometer to measure wind speed and indicate its direction.
His sketch, made in the late fifteenth century, shows a vertical board or vane that could be moved by air. A scale would let an observer compare how far the wind shifted the indicator, providing a practical estimate of wind strength. Leonardo wanted such measurements for studying flight and atmospheric conditions.
The invention is an early form of the anemometer, the general name still used for wind-speed instruments. Modern cup, vane, hot-wire, and ultrasonic anemometers use more precise mechanisms, but they serve the same basic purpose.
It is sometimes mislabeled a weather “barometer.” A barometer measures air pressure, while Leonardo's device responded directly to moving air.