The New Student's Reference Work/Windmill
Wind'mill', a wheel driven by wind to obtain power. Windmills vary in diameter from eight to thirty feet. The largest sizes in ordinary wind developing as high as four H. P. The ordinary pumping-wheel develops less than one quarter H. P. For service requiring small power, and where constant operation is not vital, as in pumping water and grinding feed, windmills are, according to Wolff, the cheapest power available. He estimates an average of eight running hours a day for most parts of the United States. The number of windmills in use is very great. American windmills practically control the market all over the world. Windmills have been in use since the twelfth century in Europe. The old-fashioned mill still in use in Holland has its arms covered with canvass, and the diameter of the wheel is generally very large. One is mentioned with a diameter of 150 feet, but a common diameter is about a third of this. These wheels are largely used for pumping water and for grinding grain. They have various schemes for setting them to face the wind, a common method in Germany being to rotate the whole tower on wheels. The windmill has been developed in the United States, along different lines, and American windmills are very superior to the older forms. The American windmill consists of a wheel with a great number of narrow, radial, inclined arms of wood or metal, the axis of the wheel being horizontal, and the direction of the wheel being regulated by an arm carrying a vane. One firm in the United States is said to make nearly 20,000 windmills annually. Windmills are unsuited to driving dynamos on account of the variation in speed.