| 摘要 |
Four wide frames are fixed to a vertical axis. The frames have horizontal bars ten centimeters apart. On each horizontal bar, a sheet of cloth twenty centimeters high and as wide as the frame is hung such that the sheets of cloth are all on the same side of the frames so that when the wind blows from any direction, the windmill rotates in the same direction. For frames facing the wind direction, on one side of the axis, the wind will blow the sheets of cloth away from the frame, and the wind will pass through the frame. On the other side of the axis, the wind will blow the sheets of cloth, but the horizontal bars will stop them from blowing to the other side of the frame such that the sheets of cloth stick to the frame and prevent the wind from passing through. The frame on that other side will act like a big sail.
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