Windmills, which normally consist of two or more glades or sails mounted on a shaft, are devices that generate power or perform other work using the force of the wind. During the 19th century, thousands of windmills were in use in Europe and the rural United States, mostly for irrigation work. The rural electrification program implemented in the U.S. from the 1930s to the 1950s brought electricity to replace the wind's power. Most modern machines fall into one of two general classes: horizontal-axis and vertical-axis. Examples of the horizontal-axis machines are the familiar multi -bladed windmills of the U.S. prairies, used primarily for pumping water.