The Waterwheel
...re efficiently. Examples of these mills still exist today in Pompeii, Herculaneum, and Ostia (Giles 1994:24). Even with this extended power, animal and slave-powered mills required constant attention (Basalla 1988:145). Although the hand-mill and larger animal-powered mills are still, today, in use in many parts of the world, approximately 2,000 years ago humankind began to harness waterpower to turn the stones that ground its grain. Water wheels and their development can be seen in three distinct types of water mills. The first and simplest type, the horizontal waterwheel(See Figure 2), seems to have directly developed from the rotary quern and is believed to have been developed in the mountains of Armenia, c.200B.C.. “It consisted of a paddle-armed wheel either laid horizontally in the stream with one side masked against the current or furnished with a chute to guide the flow. Suited to streams with a small volume of water and moderate current, it could be readily harnessed to a grain mill by extending the vertical axle upward to a rotating millstone (Giles 1994:33).” The axle passed through the lower horizontal millstone to rotate the upper stone. Since there was no gearing, the speed of the turbine was the same at which the upper stone was turned. Horizontal water wheels are still found today in many parts of the world, but only in those areas where the river system will allow the water to be run through narrow channels and ultimately down a steep chute directed onto the blades of the wheel (Hodges 1970:192). The horizontal wheel was soon replaced by the more efficient vertical waterwheel. The vertical waterwheel originated in the eastern Mediterranean region, 150-100 B.C.(Basalla 1988:144). This type probably was derived from a “noria,” a water-lifting device developed in either Persia or India. “In its original form, the noria was a large vertical wheel, its circumference armed with buckets, that was turned by oxen circling a capstan or walking treadmill (Giles 1994:34).” When mounted in a rapidly flowing stream, the current was enough to turn the wheel of the noria, which in turn led to the development of the vertical waterwheel. Two basic types of vertical waterwheel exist: the undershot and the overshot wheels. Both varieties of the vertical waterwheel require the use of gears to transfer the force of the water to the milling mechanism. An undershot wheel (See Figure 3) uses the kinetic energy of the water striking the paddles to turn the wheel (Syson 1980:64). “There are two main kinds of undershot wheels:– one which is worked by a stream without a sluice and the second that is operated by a head of water built up behind a sluice gate. The former kind has a mechanical efficiency of some 35 per cent. The latter type can be sub-divided into two and if the water strikes the paddles at about the level of the axle the wheel is called a high-breast wheel. Wheels that are operated by the stream meeting the paddles below the axles are called low-breast wheels. High and low breast wheels are 55-60 percent efficient (Vince 1984:9).” The overshot wheel(See Figure 4), appearing by the fifth century A.D., is far more efficient than the undershot wheel. It does, however, require a site where there is a good fall of water to generate enough power to make the wheel useful. If the flow of water was not considerable, the water was ponded back in a mill-pool and directed by means of a chute over the top of the waterwheel (Hodges 1970:196). Overshot wheels rotate in the opposite direction to the undershot type and the efficiency of the overshot wheel is about 70 percent (Vince 1984:10). The overshot wheel needs only about a quarter of the volume of water needed by an undershot wheel because it not only has the velocity of the water to its advantage, but also the weight of the water (Syson 1980:69). Given these facts, the superiority of the overshot wheel to the previous forms is obvious. As well as its roots in Europe, waterpower had also come about in China around 100 B.C.. In China, however, the water powered rotary mills appeared before animal-powered, ‘dry water mills.’ The water mill spread to Korea, Japan and Tibet early in the Thang Dynasty. The Asians more commonly used the horizontal wheel, though the vertical wheel was known and the vertical fall of water was used in other devices. The most momentous application of Chinese waterpower was its use in the “driving mechanized astronomical instruments and finally timekeepers. A succession of planetary models, armillary spheres, and mechanically rotated star maps culminated in A.D. 1090 in a forty-foot-high tower clock built in Khaifeng, capital of the Northern Sung dynasty (Giles 1994:89).” The Chinese saw the potential of waterpower which is evident by its many remarkable uses. Though the waterwheel is believed to have been developed c. 150 B.C., it did not gain popularity in Europe until the around the fifth century A.D.. Terry S. Reynolds describes several reasons for the delay of widespread use of the waterwheel. First, the wheels built in antiquity were not constructed to use the full amount of avail...