Power for Technology: Water

Sources

Waterwheels. The Romans used waterwheels for various industrial applications, but they were not exploited to their fullest potential until the Middle Ages, when new configurations of the watermill allowed them to do heavy work even when powered by modest streams. A watermill was often the centerpiece of any village in western Europe—and in the European settlements of North America, where, after the church, the first structures built were mills to produce things such as flour, lumber, iron, and mash (for brewing).

Available Water Sources. Waterwheels were especially prevalent in western Europe during the Middle Ages. The reason was geographical. Because that part of Europe receives more rainfall than the Mediterranean basin, it has more rivers and streams that flow swiftly and year round. Mills could be located in more areas than were possible in the Roman Empire, and since rivers flowed all year, it was economically feasible to build

them, even though they, like modern factories, were expensive to construct and maintain. If a mill could be used for perhaps only three months during the winter rainy season or if the only usable flowing water were high in the mountains, where it was hard to build a mill and to bring raw materials to it, then there was little incentive to construct one. In the fertile valleys of France, Germany, and England, however, water was plentiful, not only to power the mills but to transport materials to and from the mills. People in those regions could be reasonably confident they could make a living, if not a large profit, from running them. Millers frequently did earn a great deal of money and were often important citizens of their town. The prevalence of the surname Miller today is one result of the importance and prevalence of millers in medieval European society. Because the miller often had a monopoly on a needed service in his town, the miller had the opportunity to overcharge or otherwise cheat his customers, and apparently many did. As Geoffrey Chaucer wrote of his miller in The Canterbury Tales (circa 1375–1400), “Well could he steal corn, and charge for it three times over. / And yet he had a thumb of gold, ’tis said.”

Replacing Manpower. After the plague swept through Europe during the late Middle Ages, killing up to one-third of the population in some areas, there was not enough manpower left to operate many hand-powered industries, so the automatic power provided by watermills became especially attractive. Although animal power was still available, animals need to eat, and with fewer people to farm the land, crop sizes were reduced, making animal power less feasible. These factors contributed to the widespread use of mills in the fourteenth and fifteenth centuries, but even before that time medieval Europeans were already relying heavily on water power.

Overshot versus Undershot Waterwheels. In ancient times there were two types of waterwheels that could be used to power mills for purposes such as grinding grain, beating rags to make paper, or running hammers to forge iron. The simplest and oldest form is the undershot waterwheel with bottom blades that are set into a swiftly flowing stream. While the undershot waterwheel is effective for fairly slow-moving rivers, in places where there is a large vertical drop, the overshot waterwheel offers more power for the same size wheel and same amount of water. At mills with overshot wheels, water is channeled along an elevated millrace from upstream and falls into buckets on the waterwheel. In this case the weight of the falling water, rather than its flow provides power to the wheel, making the overshot wheel about three times more efficient. Around 1450–1500 (or later), a hybrid model, combining the best features of overshot and undershot wheels, was introduced. At mills with this breast-shot wheel, swiftly flowing water is channeled into buckets on the upstream side of the wheel and the lower part of wheel is set in the flowing water. Thus, the breast-shot wheel is powered by the weight of the water and its impact.

Grinding Grain. All these waterwheels have limitations. They rotate in a vertical plane with a horizontal axle, like a Ferris wheel. Millstones for grinding grain, however, rotate in a horizontal plane with a vertical axle. So in order to grind grain, far and away the most common and important use of mills in the Middle Ages, the turning horizontal axle of the waterwheel has to be connected to the turning vertical axle of the millstone through a set

of gears. Frequently, additional intermediate gears were added to increase the speed of the millstone. Because of all these gears, some of the power of the waterwheel was lost to friction. This problem motivated medieval people to become adept at the use of gears in mechanisms, developing technology that was later employed in more-complex devices such as clocks.

Norse Mills. There was one other type of waterwheel used throughout Europe and on its northern and western fringes from fairly early in the Middle Ages until well into the modern period. It was called the Norse mill because it was primarily found in Norway, Denmark, and Scandinavian settlements in Ireland—but it seems to have originated in Asia Minor (modern-day Turkey) during the second century B.C.E. The Norse mill used a narrow stream of water directed obliquely against angled or scoop-shaped blades on a horizontal wheel. Since the horizontal wheel had a vertical axle, this same axle could be used as the axle for a millstone, making Norse mills simple to construct. They were not as powerful as mills with overshot wheels. The configuration of the Norse mill was the model for the modern turbine, used in virtually all hydro-electric installations around the world.

Bridge Mills. Because the remains of mills are often easy to find in the landscape, archeologists and historians have been able to ascertain that many cities owe their locations to convenient waterfalls or cataracts on rivers, where it was advantageous to erect mills. Undershot mills were often placed under the arches of bridges over rivers. Because water speeds up to fit through the narrow spaces between bridge piers, a bridge creates a mill race. When a mill wheel was placed under a bridge, however, boats could no longer go through the archway it occupied. Often boat captains and millers both wanted to use the main channels in the river because they provided the deepest water for boats and the swiftest water for mills. The problem was usually solvable if a bridge had several arches. In some places, however, there were so many mill wheels that they impeded boat traffic up and down a river. In rural areas mill owners often built dams or weirs to improve the efficiency of their mills or to store water to use when the rivers were low. These dams and weirs also impeded boats. Conflicts between millers and boatmen spilled over into manorial, town, and even royal courts, and there was a whole body of laws governing riparian (river) rights.

Wear and Tear. Because of the constant force of the water, waterwheels needed frequent repairs and replacement, and a storm surge could quickly destroy a mill. If possible, a watermill was fed by its own millrace, which allowed it to be sheltered to some extent from the main stream. When its millrace was shut with a sluice gate, a mill often had a good chance of survival.

Limitations of Water Power. Not all medieval Europeans lived near flowing streams and rivers. While northwestern Europe is blessed with more water than the Mediterranean world, by the time rivers reach France and Holland they are wide, meandering waterways that slowly empty into the sea. An undershot wheel needs at least a modest flow, and an overshot or breast wheel needs a significant drop in the elevation of the river. Some parts of European rivers, especially near their mouths, do not have such drops. People living in these areas could not effectively use water to power their mills.

Sources

Marjorie Nice Boyer, “Water Mills: A Problem for the Bridges and Boats of Medieval France,” History of Technology, 7 (1982): 1–22.

Frances and Joseph Gies, Cathedral, Forge and Waterwheel: Technology and Invention in the Middle Ages (New York: HarperCollins, 1994).

Elizabeth Bradford Smith and Michael Wolfe, eds., Technology and Resource Use in Medieval Europe: Cathedrals, Mills, and Mines (Alder-shot, U.K. & Brookfield, Vt.: Ashgate, 1997).

Paolo Squatriti, ed., Working with Water in Medieval Europe: Technology and Resource-Use (Leiden & Boston: Brill, 2000).