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An overshot waterwheel standing

42 ft (13 m) high powers the Old Mill

at Berry College in Rome, Georgia,

USA

Water wheelFrom Wikipedia, the free encyclopedia

(Redirected from Waterwheel)

A water wheel is a machine for converting the energy of free-flowing orfalling water into useful forms of power, often in a watermill. A waterwheel consists of a large wooden or metal wheel, with a number ofblades or buckets arranged on the outside rim forming the drivingsurface. Most commonly, the wheel is mounted vertically on a horizontalaxle, but the tub or Norse wheel is mounted horizontally on a verticalshaft. Vertical wheels can transmit power either through the axle or via aring gear and typically drive belts or gears; horizontal wheels usuallydirectly drive their load.

Water wheels were still in commercial use well into the 20th century, butthey are no longer in common use. Prior uses of water wheels includemilling flour in gristmills and grinding wood into pulp for papermaking, butother uses include hammering wrought iron, machining, ore crushing andpounding fiber for use in the manufacture of cloth.

Some water wheels are fed by water from a mill pond, which is formedwhen a flowing stream is dammed. A channel for the water flowing to orfrom a water wheel is called a mill race (also spelled millrace) or simply a"race", and is customarily divided into sections. The race bringing waterfrom the mill pond to the water wheel is a headrace; the one carrying

water after it has left the wheel is commonly referred to as a tailrace.[1]

John Smeaton's scientific investigation of the water wheel led tosignificant increases in efficiency in the mid to late 18th century and

supplying much needed power for the Industrial Revolution.[2][3]

Water wheels began being displaced by the smaller, less expensive and more efficient turbine developed by Benoît

Fourneyron, beginning with his first model in 1827.[3] Turbines are capable of handling high heads, or elevations,that exceed the capability of practical sized waterwheels.

The main difficulty of water wheels is their dependence on flowing water, which limits where they can be located.Modern hydroelectric dams can be viewed as the descendants of the water wheel as they too take advantage of themovement of water downhill. They use a turbine instead of a wheel though.

Contents

1 History

1.1 Greco-Roman world

1.1.1 Drainage wheels

1.1.2 Watermilling

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Water wheel powering a mine hoist in

De re metallica (1566)

1.1.3 Navigation

1.2 Early Medieval Europe

1.2.1 Domesday inventory of English mills ca. 1086

1.2.2 Locations

1.2.3 Economic influence

1.2.4 Applications of the water wheel in medievalEurope

1.2.5 Importance to 17th- and 18th-century Europe

(scientific influence)

1.3 Industrial European usage

1.4 China

1.5 India

1.6 Islamic world

2 Types

2.1 Horizontal wheel

2.2 Undershot wheel

2.3 Breastshot wheel2.4 Overshot wheel

2.4.1 Reversible wheel2.5 Backshot wheel

2.6 Hydraulic wheel2.7 Hydraulic wheel part reaction turbine

3 Efficiency

3.1 Power calculations4 Water-lifting

4.1 Greece5 Uses

6 Construction6.1 Headrace, tailrace

6.2 Materials7 See also

8 Notes9 References10 External links

11 Bibliography

History

Further information: Watermill

The two main functions of water wheels were historically water-lifting for irrigation purposes and as a powersource. In terms of power source, water wheels can be turned either by human or animal force or by the watercurrent itself. Water wheels come in two basic designs, either equipped with a vertical or a horizontal axle. The

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Sequence of wheels found in Rio

Tinto mines

Reconstruction of Vitruvius'

undershot-wheeled watermill

latter type can be subdivided, depending on where the water hits the wheel paddles, into overshot, breastshot andundershot wheels.

Greco-Roman world

See also: List of ancient watermills

The ancient Greeks invented the water wheel and were, along with the Romans, the first to use it for both irrigation

and as a power source. [4] The technological breakthrough occurred in the technically advanced and scientifically

minded Hellenistic period between the 3rd and 1st century BC.[5]

Drainage wheels

The Romans used water wheels extensively in mining projects. Theywere reverse overshot water-wheels designed for dewatering deep

underground mines.[citation needed] Several such devices were describedby Vitruvius. The one found during modern mining at the copper mines atRio Tinto in Spain involved 16 such wheels stacked above one anotherso as to lift water about 80 feet (24 m) from the mine sump. Part of asimilar wheel dated to about 90 AD, was found in the 1930s, atDolaucothi, a Roman gold mine in south Wales.

Watermilling

Taking indirect evidence into accountfrom the work of the Greek technicianApollonius of Perge, the Britishhistorian of technology M.J.T. Lewisdates the appearance of the vertical-axle watermill to the early 3rd century BC,and the horizontal-axle watermill to around 240 BC, with Byzantium and

Alexandria as the assigned places of invention.[6] A watermill is reported by theGreek geographer Strabon (ca. 64 BC–AD 24) to have existed sometime before71 BC in the palace of the Pontian king Mithradates VI Eupator, but its exact

construction cannot be gleaned from the text (XII, 3, 30 C 556).[7]

The first clear description of a geared watermill offers the late 1st century BCRoman architect Vitruvius who tells of the sakia gearing system as being applied

to a watermill.[8] Vitruvius's account is particularly valuable in that it shows howthe watermill came about, namely by the combination of the separate Greekinventions of the toothed gear and the water wheel into one effective mechanical

system for harnessing water power.[9] Vitruvius's water wheel is described asbeing immersed with its lower end in the watercourse so that its paddles could be driven by the velocity of the

running water (X, 5.2).[10]

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Schematic of the Roman Hierapolis

sawmill, Asia Minor, powered by a

breastshot wheel

Ox-powered Roman paddle wheel

boat from a 15th-century copy of De

Rebus Bellicis

About the same time, the overshot wheel appears for the first time in a poem by Antipater of Thessalonica, which

praises it as a labour-saving device (IX, 418.4–6).[11] The motif is also taken up by Lucretius (ca. 99-55 BC) wholikens the rotation of the water wheel to the motion of the stars on the

firmament (V 516).[12] The third horizontal-axled type, the breastshotwater wheel, comes into archaeological evidence by the late 2nd century

AD context in central Gaul.[13] Most excavated Roman watermills wereequipped with one of these wheels which, although more complex toconstruct, were much more efficient than the vertical-axle water

wheel.[14] In the 2nd century AD Barbegal watermill complex a series ofsixteen overshot wheels was fed by an artificial aqueduct, a proto-industrial grain factory which has been referred to as "the greatest known

concentration of mechanical power in the ancient world".[15]

In Roman North Africa, several installations from around 300 AD werefound where vertical-axle water wheels fitted with angled blades wereinstalled at the bottom of a water-filled, circular shaft. The water from the mill-race which entered the pit tangentiallycreated a swirling water column that made the fully submerged wheel act like true water turbines, the earliest known

to date.[16]

Navigation

Apart from its use in milling and water-raising, ancient engineers appliedthe paddled water wheel for automatons and in navigation. Vitruvius (X9.5-7) describes multi-geared paddle wheels working as a shipodometer, the earliest of its kind. The first mention of paddle wheels as ameans of propulsion comes from the 4th–5th century military treatise DeRebus Bellicis (chapter XVII), where the anonymous Roman author

describes an ox-driven paddle-wheel warship.[17]

Early Medieval Europe

See also: List of early medieval watermills

Ancient water-wheel technology continued unabated in the earlymedieval period where the appearance of new documentary genres such as legal codes, monastic charters, but also

hagiography was accompanied with a sharp increase in references to watermills and wheels.[18]

The earliest vertical-wheel in a tide mill is from 6th century Killoteran near Waterford, Ireland,[19] while the first

known horizontal-wheel in such a type of mill is from the Irish Little Island (c. 630).[20] As for the use in a commonNorse or Greek mill, the oldest known horizontal-wheels were excavated in the Irish Ballykilleen, dating to c.

636.[20]

The earliest excavated water wheel driven by tidal power was the Nendrum Monastery mill in Northern Irelandwhich has been dated at 787A.D. although a possible earlier mill dates to 619A.D. Tide mills became common inestuaries with a good tidal range in both Europe and America generally using undershot wheels.

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Water wheel powering a

small village mill at the

Museum of Folk

Architecture and Life,

Uzhhorod, Ukraine

Cistercian monasteries, in particular, made extensive use of water wheels topower watermills of many kinds. An early example of a very large water wheel isthe still extant wheel at the early 13th century Real Monasterio de NuestraSenora de Rueda, a Cistercian monastery in the Aragon region of Spain. Gristmills (for corn) were undoubtedly the most common, but there were alsosawmills, fulling mills and mills to fulfil many other labour-intensive tasks. Thewater wheel remained competitive with the steam engine well into the IndustrialRevolution. At around the eighth to 10th century, a number of Irrigationtechnologies were brought into Spain and thus introduced to Europe. One ofthose technologies is the Noria, which is basically a wheel fitted with buckets onthe peripherals for lifting water. It is similar to the undershot water wheelmentioned later in this article. It allowed peasants to power watermills moreefficiently. According to Thomas Glick's book, Irrigation and Society inMedieval Valencia, the Noria probably originated from somewhere in Persia. Ithas been used for centuries before the technology was brought into Spain by

Arabs who had adopted it from the Romans. Thus the distribution of the Noria in the Iberian peninsula "conforms to

the area of stabilized Islamic settlement".[21] This technology has a profound effect on the life of peasants. TheNoria is relatively cheap to build. Thus it allowed peasants to cultivate land more efficiently in Europe. Togetherwith the Spaniards, the technology then spread to North Africa and later to the New World in Mexico and SouthAmerica following Spanish expansion.

Domesday inventory of English mills ca. 1086

The assembly convened by William of Normandy, commonly referred to as the “Domesday” or Doomsday survey,took an inventory of all potentially taxable property in England, which included over six thousand mills spread

across three thousand different locations.[22][23]

Locations

The type of water wheel selected was dependent upon the location. Generally if only small volumes of water andhigh waterfalls were available a millwright would choose to use an overshot wheel. The decision was influenced by

the fact that the buckets could catch and use even a small volume of water.[24] For large volumes of water withsmall waterfalls the undershot wheel would have been used, since it was more adapted to such conditions andcheaper to construct. So long as these water supplies were abundant the question of efficiency remained irrelevant.By the 18th century with increased demand for power coupled with limited water locales, an emphasis was made

on efficiency scheme.[24]

Economic influence

By the eleventh century there were parts of Europe where the exploitation of water was commonplace.[22] Thewater wheel is understood to have actively shaped and forever changed the outlook of Westerners. Europe beganto transition from muscle labour, human and animal labor, towards mechanical labour with the advent of the WaterWheel. Medievalist Lynn White Jr. contended that the spread of inanimate power sources was eloquent testimony

to the emergence of the West of a new attitude toward, power, work, nature, and above all else technology.[22]

Even the most conservative commentators regarding the extent to which the water wheel influenced Medievalwestern technology and science recognize the basic elements of a power-based economy responsible for

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Ore stamp mill (behind worker raking

ore form chute). From: Georg

Agricola's De re metallica (1556)

distinguishing the Europeans above all others, had begun with the framework instilled by the water wheel.Furthermore Europeans, for the first time had begun to show their own capabilities for mechanized innovations, by

not limited themselves to merely water, but by beginning to experiment with wind and tidal mills.[25] Waterwheelsinfluenced the construction of cities, more specifically canals. The techniques that developed during this early periodsuch as stream jamming and the building of canals, put Europe on a hydraulically focused path, for instance water

supply and irrigation technology was combined to modify supply power of the wheel.[26] Illustrating the extent towhich there was a great degree of technological innovation that met the growing needs of the feudal state.

Applications of the water wheel in medieval Europe

The water mill was used for grinding grain, producing flour for bread,

malt for beer, or coarse meal for porridge.[27] Hammermills used thewheel to operate hammers. One type was fulling mill, which was used forcloth making. The trip hammer was also used for making wrought ironand for working iron into useful shapes, an activity that was otherwiselabour intensive. One application attributed from hammer milling was“rod ironing“. The water wheel was also used in papermaking, beatingmaterial to a pulp.

Importance to 17th- and 18th-century Europe (scientific influence)

Millwrights distinguished between the two forces, impulse and weight, atwork in water wheels long before 18th-century Europe. Fitzherbert, a16th-century agricultural writer, wrote “druieth the wheel as well as with

the weight of the water as with strengthe [impulse].”[28] Leonardo daVinci also discussed water power, noting “the blow [of the water] is notweight, but excites a power of weight, almost equal to its own

power.”[29] However, even realisation of the two forces, weight and impulse, confusion remained over theadvantages and disadvantages of the two, and there was no clear understanding of the superior efficiency of

weight.[30] Prior to 1750 it was unsure as to which force was dominant and was widely understood that both forces

were operating with equal inspiration amongst one another.[31] The waterwheel, sparked questions of the laws ofnature, specifically the laws of force. Torricellos work on water wheels, used an analysis of Galileo’s work onfalling bodies, that the velocity of a water sprouting from an orifice under its head was exactly equivalent to the

velocity a drop of water acquired in falling freely from the same height.[31]

Industrial European usage

The most powerful water wheel built in the United Kingdom was the 100 hp Quarry Bank Mill Water wheel nearManchester. A high breastshot design, it was retired in 1904 and replaced with several turbines. It has now beenrestored and is a museum open to the public.

The biggest working water wheel in mainland Britain has a diameter of 15.4 m and was built by the De Wintoncompany of Caernarfon. It is located within the Dinorwic workshops of the National Slate Museum in Llanberis,North Wales.

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The great water wheel in the Welsh

National Slate Museum

The largest working water wheel in the world is the Laxey Wheel (alsoknown as Lady Isabella) in the village of Laxey, Isle of Man. It is 72 feet6 inches (22.10 m) in diameter and 6 feet (1.83 m) wide and ismaintained by Manx National Heritage.

Development of water turbines during the Industrial revolution led todecreased popularity of water wheels. The main advantage of turbines isthat ability to harness head much greater than the diameter of the turbine,whereas a water wheel cannot effectively harness head greater than itsdiameter. The migration from water wheels to modern turbines tookabout one hundred years.

China

Chinese water wheels almost certainly have a separate origin, as early ones there were invariably horizontal waterwheels. By at least the 1st century AD, the Chinese of the Eastern Han Dynasty were using water wheels to crushgrain in mills and to power the piston-bellows in forging iron ore into cast iron.

In the text known as the Xin Lun written by Huan Tan about 20 AD (during the usurpation of Wang Mang), itstates that the legendary mythological king known as Fu Xi was the one responsible for the pestle and mortar,which evolved into the tilt-hammer and then trip hammer device (see trip hammer). Although the author speaks ofthe mythological Fu Xi, a passage of his writing gives hint that the water wheel was in widespread use by the 1stcentury AD in China (Wade-Giles spelling):

Fu Hsi invented the pestle and mortar, which is so useful, and later on it was cleverly improvedin such a way that the whole weight of the body could be used for treading on the tilt-hammer(tui), thus increasing the efficiency ten times. Afterwards the power of animals—donkeys,mules, oxen, and horses—was applied by means of machinery, and water-power too used for

pounding, so that the benefit was increased a hundredfold.[32]

In the year 31 AD, the engineer and Prefect of Nanyang, Du Shi (d. 38), applied a complex use of the water wheeland machinery to power the bellows of the blast furnace to create cast iron. Du Shi is mentioned briefly in the Bookof Later Han (Hou Han Shu) as follows (in Wade-Giles spelling):

In the seventh year of the Chien-Wu reign period (31 AD) Tu Shih was posted to be Prefect ofNanyang. He was a generous man and his policies were peaceful; he destroyed evil-doers andestablished the dignity (of his office). Good at planning, he loved the common people andwished to save their labor. He invented a water-power reciprocator (shui phai) for the castingof (iron) agricultural implements. Those who smelted and cast already had the push-bellows toblow up their charcoal fires, and now they were instructed to use the rushing of the water (chishui) to operate it ... Thus the people got great benefit for little labor. They found the 'water(-

powered) bellows' convenient and adopted it widely.[33]

Water wheels in China found practical uses such as this, as well as extraordinary use. The Chinese inventor ZhangHeng (78–139) was the first in history to apply motive power in rotating the astronomical instrument of an armillary

sphere, by use of a water wheel.[34] The mechanical engineer Ma Jun (c. 200–265) from Cao Wei once used awater wheel to power and operate a large mechanical puppet theater for the Emperor Ming of Wei (r. 226-

239).[35]

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Two types of hydraulic-powered

chain pumps from the Tiangong

Kaiwu of 1637, written by the Ming

Dynasty encyclopedist, Song

Yingxing (1587-1666).

India

The early history of the watermill in India is obscure. Ancient Indian textsdating back to the 4th century BC refer to the term cakkavattaka(turning wheel), which commentaries explain as arahatta-ghati-yanta(machine with wheel-pots attached). On this basis, Joseph Needhamsuggested that the machine was a noria. Terry S. Reynolds, however,argues that the "term used in Indian texts is ambiguous and does notclearly indicate a water-powered device." Thorkild Schiøler argued that itis "more likely that these passages refer to some type of tread- or hand-operated water-lifting device, instead of a water-powered water-lifting

wheel."[36]

According to Greek historical tradition, India received water-mills fromthe Roman Empire in the early 4th century AD when a certainMetrodoros introduced "water-mills and baths, unknown among them

[the Brahmans] till then".[37] Irrigation water for crops was provided byusing water raising wheels, some driven by the force of the current in theriver from which the water was being raised. This kind of water raisingdevice was used in ancient India, predating, according to Pacey, its use in

the later Roman Empire or China,[38] even though the first literary,archaeological and pictorial evidence of the water wheel appeared in the

Hellenistic world.[4]

Around 1150, the astronomer Bhaskara Achārya observed water-raisingwheels and imagined such a wheel lifting enough water to replenish the

stream driving it, effectively, a perpetual motion machine.[39] Theconstruction of water works and aspects of water technology in India isdescribed in Arabic and Persian works. During medieval times, thediffusion of Indian and Persian irrigation technologies gave rise to anadvanced irrigation system which bought about economic growth and

also helped in the growth of material culture.[40]

Islamic world

See also: Muslim Agricultural Revolution

Arab engineers took over the water technology of the hydraulic societies of the ancient Near East; they adopted theGreek water wheel as early as the 7th century, excavation of a canal in the Basra region discovered remains of awater wheel dating from this period. Hama in Syria still preserves one of its large wheels, on the river Orontes,

although they are no longer in use.[41] One of the largest had a diameter of about 20 metres and its rim was dividedinto 120 compartments. Another wheel that is still in operation is found at Murcia in Spain, La Nora, and althoughthe original wheel has been replaced by a steel one, the Moorish system during al-Andalus is otherwise virtually

unchanged. Some medieval Islamic compartmented water wheels could lift water as high as 30 meters.[42]

Muhammad ibn Zakariya al-Razi's Kitab al-Hawi in the 10th century described a noria in Iraq that could lift asmuch as 153,000 litres per hour, or 2550 litres per minute. This is comparable to the output of modern Norias in

East Asia which can lift up to 288,000 litres per hour, or 4800 litres per minute.[43]

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The norias of Hama on the

Orontes River Water wheel in Djambi,

Sumatra, c. 1918

The industrial uses of watermills in the Islamic world date back to the 7th century, while horizontal-wheeled andvertical-wheeled water mills were both in widespread use by the 9th century. A variety of industrial watermills wereused in the Islamic world, including gristmills, hullers, sawmills, shipmills, stamp mills, steel mills, sugar mills, and tidemills. By the 11th century, every province throughout the Islamic world had these industrial watermills in operation,

from al-Andalus and North Africa to the Middle East and Central Asia.[44] Muslim and Christian engineers alsoused crankshafts and water turbines, gears in watermills and water-raising machines, and dams as a source of

water, used to provide additional power to watermills and water-raising machines.[45] Fulling millsand steel millsmay have spread from Islamic Spain to Christian Spain in the 12th century. Industrial water mills were also

employed in large factory complexes built in al-Andalus between the 11th and 13th centuries.[46]

The engineers of the Islamic world developedseveral solutions to achieve the maximum outputfrom a water wheel. One solution was to mountthem to piers of bridges to take advantage ofthe increased flow. Another solution was theshipmill, a type of water mill powered by waterwheels mounted on the sides of ships moored inmidstream. This technique was employed alongthe Tigris and Euphrates rivers in 10th centuryIraq, where large shipmills made of teak andiron could produce 10 tons of flour from corn

every day for the granary in Baghdad.[47] Theflywheel mechanism, which is used to smoothout the delivery of power from a driving deviceto a driven machine, was invented by IbnBassal (fl. 1038-1075) of Al-Andalus; hepioneered the use of the flywheel in the saqiya

(chain pump) and noria.[48] The engineers Al-Jazari in the 13th century and Taqial-Din in the 16th century described many inventive water-raising machines in their technological treatises. They alsoemployed water wheels to power a variety of devices, including various water clocks and automata.

Types

Most water wheels in the United Kingdom and the United States are (or were) vertical wheels rotating about ahorizontal axle, but in the Scottish highlands and parts of southern Europe mills often had a horizontal wheel (with avertical axle). Water wheels are classified by the way in which water is applied to the wheel, relative to the wheel'saxle. Overshot & pitchback water wheels are suitable where there is a small stream with a height difference of morethan 2 meters, often in association with a small reservoir. Breastshot and undershot wheels can be used on rivers orhigh volume flows with large reservoirs.

Horizontal wheel

Commonly called a tub wheel or Norse mill, the horizontal wheel is essentially a very primitive and inefficient formof the modern turbine. It is usually mounted inside a mill building below the working floor. A jet of water is directedon to the paddles of the water wheel, causing them to turn; water exits beneath the wheel, generally through thecenter. This is a simple system, usually used without gearing so that the vertical axle of the water wheel becomes thedrive spindle of the mill.

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Undershot water wheel

Breastshot water wheel

Overshot water wheel

Sabegien, Poncelet and

Zuppinger water wheel

Undershot wheel

An undershot wheel (also called a stream wheel[49]) is a verticallymounted water wheel that is rotated by water striking paddles or bladesat the bottom of the wheel. The name undershot comes from this strikingat the bottom of the wheel. This type of water wheel is the oldest type ofwheel.

It is also regarded as the least efficienttype, although subtypes of this waterwheel (e.g. the Poncelet wheel, Sagebienwheel and Zuppinger wheel) allowsomewhat greater efficiencies than thetraditional undershot wheels. Theadvantages of undershot wheels are thatthey are somewhat cheaper and simpler tobuild, and have less of an environmentalimpact—as they do not constitute a majorchange of the river. Their disadvantagesare—as mentioned before—lessefficiency, which means that they generateless power and can only be used wherethe flow rate is sufficient to providetorque.

Undershot wheels gain no advantage fromhead. They are most suited to shallowstreams in flat country.

Undershot wheels are also well suited to installation on floating platforms.The earliest were probably constructed by the Byzantine generalBelisarius during the siege of Rome in 537. Later they were sometimesmounted immediately downstream from bridges where the flowrestriction of arched bridge piers increased the speed of the current.

Breastshot wheel

A vertically mounted water wheel that is rotated by falling water strikingbuckets near the center of the wheel's edge, or just above it, is said to bebreastshot. Breastshot wheels are the most common type in the United

States of America[citation needed] and are said to have powered theAmerican industrial revolution.

Breastshot wheels are less efficient than overshot wheels (see below),are more efficient than undershot wheels, and are not backshot (seebelow). The individual blades of a breastshot wheel are actually buckets,as are those of most overshot wheels, and not simple paddles like those of most undershot wheels. A breastshotwheel requires a good trash rack and typically has a masonry "apron" closely conforming to the wheel face, which

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The Anderson Mill of Texas is

undershot, backshot, and overshot

using two sources of water. This

allows the speed of the wheel to be

controlled.

Replica of a reversible

wheel with a 9.5 m

diameter in Clausthal-

Zellerfeld

helps contain the water in the buckets as they progress downwards. Breastshot wheels are preferred for steady,high-volume flows such as are found on the fall line of the North American East Coast.

Overshot wheel

A vertically mounted water wheel that is rotated by falling water strikingpaddles, blades or buckets near the top of the wheel is said to beovershot. In true overshot wheels the water passes over the top of thewheel, but the term is sometimes applied to backshot or pitchbackwheels where the water goes down behind the water wheel.

A typical overshot wheel has the water channeled to the wheel at the topand slightly beyond the axle. The water collects in the buckets on thatside of the wheel, making it heavier than the other "empty" side. Theweight turns the wheel, and the water flows out into the tail-water whenthe wheel rotates enough to invert the buckets. The overshot design canuse all of the water flow for power (unless there is a leak) and does notrequire rapid flow.

Unlike undershot wheels, overshot wheels gain a double advantage from gravity. Not only is the momentum of theflowing water partially transferred to the wheel, the weight of the water descending in the wheel's buckets alsoimparts additional energy. The mechanical power derived from an overshot wheel is determined by the wheel'sphysical size and the available head, so they are ideally suited to hilly or mountainous country. On average, theundershot wheel uses 22 percent of the energy in the flow of water, while an overshot wheel uses 63 percent, as

calculated by English civil engineer John Smeaton in the 18th century.[50]

Overshot wheels demand exact engineering and significant head, which usually means significant investment inconstructing a dam, millpond and waterways. Sometimes the final approach of the water to the wheel is along alengthy flume or penstock.

Reversible wheel

A special type of overshot wheel is the reversible water wheel. This has two sets ofblades or buckets running in opposite directions, so that it can turn in either directiondepending on which side the water is directed. Reversible wheels were used inmining industry in order to power various means of ore conveyance. By changing thedirection of the wheel, barrels or baskets of ore could be lifted up or lowered downa shaft. As a rule there was also a cable drum or a chain basket (German:Kettenkorb) on the axle of the wheel. It was also essential that the wheel hadbraking equipment in order to be able to stop the wheel (known as a braking wheel).The oldest known drawing of a reversible water wheel was by Georgius Agricolaand dates to 1556.

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Pitchback or "backshot" water wheel

Backshot wheel at New

Lanark World Heritage

Site, Scotland

Backshot wheel

A backshot wheel (also calledpitchback) is a variety of overshot wheelwhere the water is introduced just behindthe summit of the wheel. It combines theadvantages from breastshot and overshotsystems, since the full amount of thepotential energy released by the fallingwater is harnessed as the water descendsthe back of the wheel.

A backshot wheel continues to functionuntil the water in the wheel pit rises well

above the height of the axle, when any other overshot wheel will bestopped or even destroyed. This makes the technique particularly suitablefor streams that experience extreme seasonal variations in flow, andreduces the need for complex sluice and tail race configurations. Abackshot wheel may also gain power from the water's current past the bottom of the wheel, and not just the weightof the water falling in the wheel's buckets.

The direction of rotation of a backshot wheel is the same as that of a breastshot wheel at the same location so it caneasily replace one, without causing the directional gearing in the mill to be changed. This would increase the poweravailable while only requiring a change to be made to the water level in the top pound, which in some cases iseconomically viable.

Hydraulic wheel

A recent development of the breastshot wheel is a hydraulic wheel which effectively incorporates automaticregulation systems. The Aqualienne is one example. It generates between 37 kW and 200 kW of electricity from a

20m³ waterflow with a head of 1 to 3.5m.[51] It is designed to produce electricity at the sites of former watermills.

Hydraulic wheel part reaction turbine

A parallel development is the hydraulic wheel/part reaction turbine that also incorporates a weir into the centre ofthe wheel but uses blades angled to the water flow. The WICON-Stem Pressure Machine (SPM) exploits this

flow.[52] Estimated efficiency 67%.

The University of Southampton School of Civil Engineering and the Environment in the UK has investigated bothtypes of Hydraulic wheel machines and has estimated their hydraulic efficiency and suggested improvements, i.e.

The Rotary Hydraulic Pressure Machine. (Estimated maximum efficiency 85%).[53]

These type of water wheels have high efficiency at part loads / variable flows and can operate at very low heads, <1 metre. Combined with direct drive Axial Flux Permanent Magnet Alternators and power electronics they offer aviable alternative for low head hydroelectric power generation.

Efficiency

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The Suspension wheel with rim-

gearing at the Portland Basin Canal

Warehouse

Two early improvements were suspension wheels and rim gearing.Suspension wheels are constructed in the same manner as a bicyclewheel, the rim being supported under tension from the hub- this led tolarger lighter wheels than the former design where the heavy spokes wereunder compression. Rim-gearing entailed adding a notched wheel to therim or shroud of the wheel. A stub gear engaged the rim-gear and tookthe power into the mill using an independent line shaft. This removed therotative stress from the axle which could thus be lighter, and also allowedmore flexibility in the location of the power train. The shaft rotation wasgeared up from that of the wheel which led to less power loss. Anexample of this designed pioneered by Thomas Hewes and refined byWilliam Fairburn can be seen at the 1849 restored wheel at the Portland

Basin Canal Warehouse.[54]

Overshot (and particularly backshot) wheels are the most efficient type; abackshot steel wheel can be more efficient (about 60%) than all but the most advanced and well-constructed

turbines. Nevertheless, in some situations an overshot wheel is preferable to a turbine.[55]

The development of the hydraulic turbine wheels with their improved efficiency (>67%) opened up an alternativepath for the installation of water wheels in existing mills, or redevelopment of abandoned mills.

Power calculations

In an undershot wheel or a run of the river wheel the power is dependant to the kinetic energy of the river.Approximate power can be calculated.

Power in Watts= 100 x A x V3 xC

A = Area of paddles in the water (square meters)

V = Velocity of the stream in meters per secondC = Efficiency Constant (assume 1 for a water to wire efficiency of 20%)

Rotational speed of the wheel = 9 x V /D rpm

D = diameter in metres

[56] For a breast shot or over shot wheel both potential energy and kinetic energy must be considered. This takesthe form of the weight of water in the buckets and the vertical distance travelled. A rule of thumb formula is

Power in Watts = 4 x Q x H x Constant

Q = Weight of water (volume per sec x capacity of the buckets)

V = Velocity of the stream in meters per secondH = Head, or height difference of water between the lip of the flume (head race) and the tailrace

C = Efficiency Constant

The optimal rotational speed of a breast shot or overshot wheel is approximately:

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Detail of azud at Aranjuez, Spain

Rotational speed of the wheel= 21/ √D

D = diameter of the wheel in metres

[56]

Water-lifting

See also:Noria

In water-raising devices rotary motion is typically more efficient than machines based on oscillating motion.[57]

The compartmented water wheel comes in two basic forms, the wheelwith compartmented body (Latin tympanum) and the wheel with

compartmented rim or a rim with separate, attached containers.[57] Thewheels could be either turned by the flow of water, men treading on its

outside or by animals by means of a sakia gear.[58] While the tympanumhad a large discharge capacity, it could lift the water only to less than the

height of its own radius and required a large torque for rotating.[58] Theseconstructional deficiencies were overcome by the wheel with a

compartmented rim which was a less heavy design with a higher lift.[59]

Greece

The earliest literary reference to a water-driven, compartmented wheelappears in the technical treatise Pneumatica (chap. 61) of the Greek

engineer Philo of Byzantium (ca. 280−220 BC).[60] In hisParasceuastica (91.43−44), Philo advises the use of such wheels for

submerging siege mines as a defensive measure against enemy sapping.[61] Compartmented wheels appear to have

been the means of choice for draining dry docks in Alexandria under the reign of Ptolemy IV (221−205 BC).[61]

Several Greek papyri of the 3rd to 2nd century BC mention the use of these wheels, but don't give further

details.[61] The non-existence of the device in the Ancient Near East before Alexander's conquest can be deduced

from its pronounced absence from the otherwise rich oriental iconography on irrigation practices.[62][63][64][65]

Unlike other water-lifting devices and pumps of the period though, the invention of the compartmented wheelcannot be traced to any particular Hellenistic engineer and may have been made in the late 4th century BC in a rural

context away from the metropolis of Alexandria.[66]

The earliest depiction of a compartmented wheel is from a tomb painting in Ptolemaic Egypt which dates to the 2ndcentury BC. It shows a pair of yoked oxen driving the wheel via a sakia gear, which is here for the first time

attested, too.[67] The Greek sakia gear system is already shown fully developed to the point that "modern Egyptian

devices are virtually identical".[67] It is assumed that the scientists of the Museum of Alexandria, at the time the most

active Greek research center, may have been involved in its invention.[68] An episode from the Alexandrian War in48 BC tells of how Caesar's enemies employed geared water wheels to pour sea water from elevated places on the

position of the trapped Romans.[69]

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Drainage wheel from Rio Tinto mines Iced water wheel

Around 300 AD, the noria was finally introduced when the wooden compartments were replaced with inexpensive

ceramic pots that were tied to the outside of an open-framed wheel.[66]

Uses

Water Wheels have traditionally been used to power mills. More recently, water wheels have been adapted for theproduction of electricity. Small scale Hydro power plants are being used to power generators, creating cleanelectricity.

Construction

A water wheel consists of a largewooden or metal wheel, with a numberof blades or buckets arranged on theoutside rim forming the driving surface.Most commonly, the wheel is mountedvertically on a horizontal axle, but thetub or Norse wheel is mountedhorizontally on a vertical shaft. Verticalwheels can transmit power eitherthrough the axle or via a ring gear andtypically drive belts or gears; horizontalwheels usually directly drive their load.

Headrace, tailrace

A mill pond is formed when a flowing stream is dammed to feed a water wheel. A channel for the water flowing toor from a water wheel is called a mill race (also spelled millrace) or simply a "race" (in Scotland it is normallyreferred to as a lade), and is customarily divided into sections. The race bringing water from the mill pond to thewater wheel is a headrace; the one carrying water after it has left the wheel is commonly referred to as a

tailrace.[1]

Materials

Traditionally water wheels have been made mostly from wood. Steel in overshot (and pitchback) wheels allowshigher speeds. A wooden wheel with a wooden axle cannot necessarily sustain high speed needed for hydroelectricpower generation.

Until around 1820 water wheels in North America were generally built with a wooden axle (usually from seasonedwhite oak) with three or more spokes extending through the wood axle and interlocked inside. Additional spokesattached to pocket holes in the axle and were wedged inside the wood axle. These wheels generally had metalgudgeons held in place on the ends of the shafts using wedges and steel hoops, which allowed the wood axle tohave a small metal tip on the end. These metal tips or "journals" would then ride on wood or stone bearings. Awater wheel made this way was called a Compass Wheel. Sometimes a wood axle would need to be replaced after

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A mid-nineteenth century

water wheel at Cromford in

England used for grinding

locally mined barytes.

only a year or two prompting the development of "hybrid wheels". After 1820, water wheels began to have steelhubs and later steel axles with wood spokes, rims, and paddles. These hybrid wheels eliminated the oftenproblematic wood axle and allowed the addition of more spokes. Later cast-iron and all-steel wheels were used.

See also

Watermill

milldamCable railway

European water wheelIan GilmartinSmall Hydro

Micro Hydro

Example applications

The following installations use a water wheel as the prime mover:

Watermills in the United KingdomClaverton Pumping Station – canal water pumping station

Derby Industrial Museum – former silk millLaxey Wheel – pumping water from a mine

Snaefell Wheel – pumping water from a mine

Water turbines

Water turbine

Pelton wheelBanki turbine

Francis turbineKaplan turbineTurgo turbine

Tyson turbine

For devices to lift water for irrigation

NoriaSakia

Hydraulic ram

Devices to lift water for land drainage

Scoop wheel

Notes

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1. ̂a b Dictionary definition of "tailrace" (http://dictionary.reference.com/browse/tailrace)

2. ^ Musson; Robinson (1969). Science and Technology in the Industrial Revolution. University of Toronto Press.p. 69.

3. ̂a b Thomson, Ross (2009). Structures of Change in the Mechanical Age: Technological Invention in the UnitedStates 1790-1865. Baltimore, MD: The Johns Hopkins University Press. p. 34. ISBN 978-0-8018-9141-0.

4. ̂a b Oleson 1984, pp. 325ff.; Oleson 2000, pp. 217–302; Donners, Waelkens & Deckers 2002, pp. 10−15;Wikander 2000, pp. 371−400

5. ^ Wikander 2000, pp. 395; Oleson 2000, p. 229It is no surprise that all the water-lifting devices that depend on subdivided wheels or cylindersoriginate in the sophisticated, scientifically advanced Hellenistic period, ...

6. ^ Wikander 2000, pp. 396f.; Donners, Waelkens & Deckers 2002, p. 11; Wilson 2002, pp. 7f.

7. ^ Wikander 1985, p. 160; Wikander 2000, p. 396

8. ^ Oleson 2000, pp. 234, 269

9. ^ Oleson 2000, pp. 269−271

10. ^ Wikander 2000, pp. 373f.; Donners, Waelkens & Deckers 2002, p. 12

11. ^ Wikander 2000, p. 375; Donners, Waelkens & Deckers 2002, p. 13

12. ^ Donners, Waelkens & Deckers 2002, p. 11; Oleson 2000, p. 236

13. ^ Wikander 2000, p. 375

14. ^ Donners, Waelkens & Deckers 2002, pp. 12f.

15. ^ Greene 2000, p. 39

16. ^ Wilson 1995, pp. 507f.; Wikander 2000, p. 377; Donners, Waelkens & Deckers 2002, p. 13

17. ^ De Rebus Bellicis (anon.), chapter XVII, text edited by Robert Ireland, in: BAR International Series 63, part 2, p.34

18. ^ Wikander 2000, pp. 372f.; Wilson 2002, p. 3

19. ^ Murphy 2005

20. ̂a b Wikander 1985, pp. 155–157

21. ^ Glick, p. 178

22. ̂a b c Robert, Friedel, A Culture of Improvement. MIT Press. Cambridge, Massachusetts. London, England.(2007). p. 31.

23. ^ Robert, Friedel, A Culture of Improvement. MIT Press. Cambridge, Massachusetts. London, England. (2007). p.32.

24. ̂a b Robert, A. Howard, Primer on Water Wheels, Vol 15, No. 3 (1983) pp26-33. Published by: Association forPreservation Technology International. p26.

25. ^ Terry S, Reynolds, Stronger than a Hundred Men; A History of the Vertical Water Wheel. Baltimore; JohnsHopkins University Press, 1983. Robert, Friedel, A Culture of Improvement. MIT Press. Cambridge,Massachusetts. London, England. (2007). p. 33.

26. ^ Robert, Friedel, A Culture of Improvement. MIT Press. Cambridge, Massachusetts. London, England. (2007). p.34

27. ^ Robert, Friedel, A Culture of Improvement. MIT Press. Cambridge, Massachusetts. London, England. (2007)

28. ^ Anthony Fitzherbert, Surveying (London, 1539, reprinted in [Robert Vansitarrt, ed] Certain Ancient TractsConcerning the Management of Landed Property Reprinted [London, 1767.] pg. 92.

29. ^ Leonardo da Vinci, MS F, 44r, in Les manuscrits de Leonardo da Vinci, ed Charles Ravaisson-Moilien (Paris,1889), vol.4; cf, Codex Madrid, vol. 1, 69r [The Madrid Codices], trans. And transcribed by Ladislao Reti (NewYork, 1974), vol. 4.

30. ^ Smeaton, “An Experiemental Inquiry Concerning the Natural Powers of Water and Wind to Turn Mills, andOther Machines, depending on Circular Motion,” Royal Society, Philosophical Transactions of the Royal Societyof London 51 (1759); 124-125

31. ̂a b Torricella, Evangelica, Opere, ed. Gino Loria and Guiseppe Vassura (Rome, 1919.)

32. ^ Needham, p. 392

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33. ^ Needham, p. 370

34. ^ Morton, p. 70

35. ^ Needham, p. 158

36. ^ Reynolds, p. 14

37. ^ Wikander 2000, p. 400:This is also the period when water-mills started to spread outside the former Empire. According toCedrenus (Historiarum compendium), a certain Metrodoros who went to India in c. A.D. 325"constructed water-mills and baths, unknown among them [the Brahmans] till then".

38. ^ Pacey, p. 10

39. ^ Pacey, p. 36

40. ^ Siddiqui

41. ^ al-Hassani et al., p.115

42. ^ Lucas, Adam (2006), Wind, Water, Work: Ancient and Medieval Milling Technology, Brill Publishers, p. 26,ISBN 90-04-14649-0

43. ^ Donald Routledge Hill (1996), A history of engineering in classical and medieval times, Routledge, pp. 145–6,ISBN 0-415-15291-7

44. ^ Lucas, p. 10

45. ^ Ahmad Y Hassan, Transfer Of Islamic Technology To The West, Part II: Transmission Of Islamic Engineering(http://www.history-science-technology.com/Articles/articles%2071.htm)

46. ^ Lucas, p.11

47. ^ Hill; see also Mechanical Engineering (http://home.swipnet.se/islam/articles/HistoryofSciences.htm))

48. ^ Ahmad Y Hassan, Flywheel Effect for a Saqiya (http://www.history-science-technology.com/Notes/Notes%204.htm).

49. ^ Stream wheel term and specifics (http://www.energy.soton.ac.uk/hydro/waterwheels.html)

50. ^ The History of Science and Technology by Bryan Bunch with Alexander Hellmans pp.114

51. ^ http://www.h3eindustries.com/How-does-an-Aqualienne%C2%AE-work? Aqualienne breastshot wheel

52. ^ Oewatec (http://www.oewatec.de)

53. ^ Low Head Hydro (http://www.energy.soton.ac.uk/hydro/waterwheels.html)

54. ^ *Nevell, Mike; Walker (2001). Portland Basin and the archaeology of the Canal Warehouse. TamesideMetropolitan Borough with University of Manchester Archaeological Unit. ISBN 1-871324-25-4.

55. ^ For a discussion of the different types of water wheels, see Syson, p. 76-91

56. ̂a b British Hydro (http://www.british-hydro.org/waterwheels.html) Water wheel information.

57. ̂a b Oleson 2000, p. 229

58. ̂a b Oleson 2000, p. 230

59. ^ Oleson 2000, pp. 231f.

60. ^ Oleson 2000, p. 233

61. ̂a b c Oleson 2000, pp. 234

62. ^ Oleson 2000, pp. 235:The sudden appearance of literary and archaeological evidence for the compartmented wheel in thethird century B.C. stand in marked contrast to the complete absence of earlier testimony, suggestingthat the device was invented not long before.

63. ^ An isolated passage in the Hebrew Deuteronomy (11.10−11) about Egypt as a country where you sowed yourseed and watered it with your feet is interpreted as a metaphor referring to the digging of irrigation channels ratherthan treading a water wheel (Oleson 2000, pp. 234).

64. ^ As for a Mesopotamian connection: Schioler 1973, p. 165−167:References to water-wheels in ancient Mesopotamia, found in handbooks and popular accounts, arefor the most part based on the false assumption that the Akkadian equivalent of the logogramGIS.APIN was nartabu and denotes an instrument for watering ("instrument for making moist").

As a result of his investigations, Laessoe writes as follows on the question of the saqiya: "I consider

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it unlikely that any reference to the saqiya will appear in ancient Mesopotamian sources." In hisopinion, we should turn our attention to Alexandria, "where it seems plausible to assume that thesaqiya was invented."

65. ^ Adriana de Miranda (2007), Water architecture in the lands of Syria: the water-wheels, L'Erma di Bretschneider,pp. 48f., ISBN 88-8265-433-8 concludes that the Akkadian passages "are couched in terms too general too allowany conclusion as to the exact structure" of the irrigation apparatus, and states that "the latest official ChicagoAssyrian Dictionary reports meanings not related to types of irrigation system".

66. ̂a b Oleson 2000, pp. 235

67. ̂a b Oleson 2000, pp. 234, 270

68. ^ Oleson 2000, pp. 271f.

69. ^ Oleson 2000, p. 271

References

al-Hassani, S.T.S., Woodcock, E. and Saoud, R. (2006) 1001 inventions : Muslim heritage in ourworld, Manchester : Foundation for Science Technology and Civilisation, ISBN 0-9552426-0-6

Allan. April 18, 2008. Undershot Water Wheel. Retrieved fromhttp://www.builditsolar.com/Projects/Hydro/UnderShot/WaterWheel.htm

Donners, K.; Waelkens, M.; Deckers, J. (2002), "Water Mills in the Area of Sagalassos: A DisappearingAncient Technology", Anatolian Studies (Anatolian Studies, Vol. 52) 52: 1–17, doi:10.2307/3643076

(http://dx.doi.org/10.2307%2F3643076), JSTOR 3643076 (http://www.jstor.org/stable/3643076)Glick, T.F. (1970) Irrigation and society in medieval Valencia, Cambridge, MA: Belknap Press ofHarvard University Press, ISBN 0-674-46675-6

Greene, Kevin (2000), "Technological Innovation and Economic Progress in the Ancient World: M.I. FinleyRe-Considered", The Economic History Review 53 (1): 29–59, doi:10.1111/1468-0289.00151

(http://dx.doi.org/10.1111%2F1468-0289.00151)Hill, D.R. (1991) "Mechanical Engineering in the Medieval Near East", Scientific American, 264 (5:May),

p. 100-105Lucas, A.R. (2005), "Industrial Milling in the Ancient and Medieval Worlds: A Survey of the Evidence for anIndustrial Revolution in Medieval Europe", Technology and Culture, 46 (1), p. 1-30,

doi:10.1353/tech.2005.0026 (http://dx.doi.org/10.1353%2Ftech.2005.0026)Lewis, M.J.T. (1997) Millstone and Hammer: the origins of water power, University of Hull Press,

ISBN 0-85958-657-XMorton, W.S. and Lewis, C.M. (2005) China: Its History and Culture, 4th Ed., New York : McGraw-

Hill, ISBN 0-07-141279-4Murphy, Donald (2005), Excavations of a Mill at Killoteran, Co. Waterford as Part of the N-25Waterford By-Pass Project (http://www.acsltd.ie/cms/uploads/02_02_kiloteran_mill_-_ucd.pdf), Estuarine/

Alluvial Archaeology in Ireland. Towards Best Practice, University College Dublin and National RoadsAuthority

Needham, J. (1965) Science and Civilization in China - Vol. 4: Physics and physical technology - Part2: Mechanical engineering, Cambridge University Press, ISBN 0-521-05803-1

Nuernbergk, D.M. (2005) Wasserräder mit Kropfgerinne: Berechnungsgrundlagen und neueErkenntnisse, Detmold : Schäfer, ISBN 3-87696-121-1Nuernbergk, D.M. (2007) Wasserräder mit Freihang: Entwurfs- und Berechnungsgrundlagen,

Detmold : Schäfer, ISBN 3-87696-122-X

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Pacey, A. (1991) Technology in World Civilization: A Thousand-year History, 1st MIT Press ed.,

Cambridge, Massachusetts : MIT, ISBN 0-262-66072-5Oleson, John Peter (1984), Greek and Roman Mechanical Water-Lifting Devices: The History of aTechnology, University of Toronto Press, ISBN 90-277-1693-5

Oleson, John Peter (2000), "Water-Lifting", in Wikander, Örjan, Handbook of Ancient WaterTechnology, Technology and Change in History 2, Leiden: Brill, pp. 217–302, ISBN 90-04-11123-9

Reynolds, T.S. (1983) Stronger Than a Hundred Men: A History of the Vertical Water Wheel, JohnsHopkins studies in the history of technology: New Series 7, Baltimore: Johns Hopkins University Press,

ISBN 0-8018-2554-7Schioler, Thorkild (1973), Roman and Islamic Water-Lifting Wheels, Odense University Press, ISBN 87-7492-090-1

Shannon, R. 1997. Water Wheel Engineering. Retrieved fromhttp://permaculturewest.org.au/ipc6/ch08/shannon/index.html.

Siddiqui, Iqtidar Husain (1986) "Water Works and Irrigation System in India during Pre-Mughal Times",Journal of the Economic and Social History of the Orient, 29 (1), p. 52–77,

doi:10.1163/156852086X00036 (http://dx.doi.org/10.1163%2F156852086X00036)Syson, l. (1965) British Water-mills, London : Batsford, 176 p.Wikander, Örjan (1985), "Archaeological Evidence for Early Water-Mills. An Interim Report", History of

Technology 10: 151–179Wikander, Örjan (2000), "The Water-Mill", in Wikander, Örjan, Handbook of Ancient Water

Technology, Technology and Change in History 2, Leiden: Brill, pp. 371–400, ISBN 90-04-11123-9Wilson, Andrew (1995), "Water-Power in North Africa and the Development of the Horizontal Water-

Wheel", Journal of Roman Archaeology 8: 499–510Wilson, Andrew (2002), "Machines, Power and the Ancient Economy", The Journal of Roman Studies 92:

1–32, doi:10.2307/3184857 (http://dx.doi.org/10.2307%2F3184857), JSTOR 3184857(http://www.jstor.org/stable/3184857)

External links

Essay/audio clip (http://www.uh.edu/engines/epi105.htm)Glossary of water wheel terms (http://www.angelfire.com/journal/millbuilder/terms.html)Persian Wheel in India, 1814-1815

(http://www.bl.uk/onlinegallery/onlineex/apac/addorimss/a/019addor0004784u00000000.html) painting withexplanatory text, at British Library website.

WaterHistory.org - Several articles concerning water wheels (http://www.waterhistory.org)- Aintreewoodcraft.com Garden water wheel (http://www.aintreewoodcraft.com)

Computer simulation of an undershot water wheel(http://mw.concord.org/modeler1.3/mirror/mechanics/undershotwaterwheel.html)Computer simulation of an overshot water wheel

(http://mw.concord.org/modeler1.3/mirror/mechanics/overshotwaterwheel.html)

Bibliography

Soto Gary, Water Wheel. vol. 163. No. 4. (Jan., 1994), p. 197

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