WIND AND OTHER POWER SOURCES
Through much of the pre-industrial age, the main power sources were derived from human and animal muscle or from water, as discussed in the previous chapters. The wind was used as a source of power in sailing but was not applied to other devices until the early part of the second millennium A.D. when windmills were used to drive corn mills, and later to drive fulling mills, water pumps, and other industrial mechanisms. Gunpowder was used, in about 1300 A.D., to provide the propulsive power of guns, and was later used in mining as an explosive but it did not find other applications. The invention of mechanical clocks driven by falling weights (gravity) prompted the application of clockwork mechanisms to other devices but although they are included here, they do not constitute a prime mover because their stored energy is usually supplied manually. Further sources of power based on hot air, or steam did not appear, despite Hero's turbine, until the Renaissance and never proceeded beyond experimental prototypes.
It is astonishing that windmills were not developed until about 3,500 years after the first use of sails. By 2700 B.C., the primitive reed boat of the Nile had developed into a more substantial structure capable of transporting rock and stone from quarries in the south to building sites in the north. From this time on there is a wealth of illustrations depicting river craft and sea going vessels with sails. Sailing ships show a continuous development from 2700 B.C. onwards and were very common, but the application of wind power to other devices did not develop. The windmill appears to have been unknown, as a source of power, to the Greeks and Romans although Hero of Alexandria describes a wind organ “with oar-like scoops like the so-called windmotors”. But nothing more is known of these wind-motors.