Ships may be made to move without oars or rowers, so that large vessels might be driven on the sea or on a river by a single man, and more swiftly than if they were strongly manned. Chariots can be built which can move without any draught animal at incalculable speed . . . Flying machines might be made in the middle of which a man might sit, turning a certain mechanism whereby artfully built wings might beat the air, in the manner of a bird in flight. Another instrument could be made which, although small, will lift or lower weights of almost infinite greatness . . . Again, instruments might
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