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A windmill is a machine which converts the energy of wind into rotational motion by means of adjustable vanes called sails. The main use is for a grinding mill powered by the wind, reducing a solid or coarse substance into pulp or minute grains, by crushing, grinding, or pressing.[1][2] Windmills have also provided energy to sawmills, paper mills, hammermills, and windpumps for obtaining fresh water from underground or for drainage (especially of land below sea level).



The windwheel of the Greek engineer Heron of Alexandria in the 1st century marks one of the first known instances of wind powering a machine in history.[3][4] Another early example of a wind-driven wheel was the prayer wheel, which was used in ancient Tibet and China since the 4th century B.C..[5]

Vertical-axis windmills

The first practical windmills were the vertical-axis windmills invented in eastern Persia (what is now Afghanistan), as recorded by the Persian geographer Estakhri in the 9th century.[6][7] The authenticity of an earlier anecdote of a windmill involving the second caliph Umar (AD 634–644) is questioned on the grounds that it appears in a 10th-century document.[8] Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind grain or draw up water, and were quite different from the later European horizontal-axis versions. Windmills were in widespread use across the Middle East and Central Asia, and later spread to China and India from there.[9]

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