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80-565: The Upper Harz Ponds also have the oldest working dams in Germany. The ponds were originally built for storing the water needed to drive the water wheels providing energy to the Upper Harz silver mines . These water wheels drove the pumps , the hoisting equipment, the stamp mills and, from 1820, the man engines as well. To begin with, the ponds merely impounded water from their natural catchment areas . But in many cases, their inflow

160-422: A habitat for some extremely rare plant communities. On the soils of many ponds coral necklace ( Ilecebrum verticillatum ), strapwort ( Corrigiola litoralis ) or shoreweed ( Littorella uniflora ) may be found growing. They are dependent on this constant fluctuation of water levels in the reservoir and so the nature conservation authorities have agreed with the pond operators an operating regime that will secure

240-681: A cheap dish in the United Kingdom . During the 1990s, their numbers collapsed across Europe. They became a delicacy, and the UK's most expensive species. Eels, particularly the moray eel , are popular among marine aquarists . Eel blood is toxic to humans and other mammals, but both cooking and the digestive process destroy the toxic protein. High consumption of eels is seen in European countries leading to those eel species being considered endangered. In 2010, Greenpeace International added

320-412: A flowing stream is dammed . A channel for the water flowing to or from a water wheel is called a mill race . The race bringing water from 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 . Waterwheels were used for various purposes from things such as agriculture to metallurgy in ancient civilizations spanning

400-399: A large head compared to other types of wheel which usually means significant investment in constructing the headrace. Sometimes the final approach of the water to the wheel is along a flume or penstock , which can be lengthy. A backshot wheel (also called pitchback ) is a variety of overshot wheel where the water is introduced just before the summit of the wheel. In many situations, it has

480-544: A poem by Antipater of Thessalonica , which praises it as a labour-saving device (IX, 418.4–6). The motif is also taken up by Lucretius (ca. 99–55 BC) who likens the rotation of the waterwheel to the motion of the stars on the firmament (V 516). The third horizontal-axled type, the breastshot waterwheel, comes into archaeological evidence by the late 2nd century AD context in central Gaul . Most excavated Roman watermills were equipped with one of these wheels which, although more complex to construct, were much more efficient than

560-449: A reversible water wheel was by Georgius Agricola and dates to 1556. As in all machinery, rotary motion is more efficient in water-raising devices than oscillating motion. In terms of power source, waterwheels can be turned by either human respectively animal force or by the water current itself. Waterwheels come in two basic designs, either equipped with a vertical or a horizontal axle. The latter type can be subdivided, depending on where

640-560: A ship odometer , the earliest of its kind. The first mention of paddle wheels as a means of propulsion comes from the 4th–5th century military treatise De Rebus Bellicis (chapter XVII), where the anonymous Roman author describes an ox-driven paddle-wheel warship. Eel see text Eels are ray-finned fish belonging to the order Anguilliformes ( / æ ŋ ˈ ɡ w ɪ l ɪ f ɔːr m iː z / ), which consists of eight suborders, 20 families , 164 genera , and about 1000 species . Eels undergo considerable development from

720-414: A vertical axle. Commonly called a tub wheel , Norse mill or Greek mill , the horizontal wheel is a primitive and inefficient form of the modern turbine. However, if it delivers the required power then the efficiency is of secondary importance. It is usually mounted inside a mill building below the working floor. A jet of water is directed on to the paddles of the water wheel, causing them to turn. This

800-484: A water wheel. The mechanical engineer Ma Jun (c. 200–265) from Cao Wei once used a water wheel to power and operate a large mechanical puppet theater for the Emperor Ming of Wei ( r. 226–239). The technological breakthrough occurred in the technologically developed Hellenistic period between the 3rd and 1st century BC. A poem by Antipater of Thessalonica praised the water wheel for freeing women from

880-567: Is a monophyletic group that originated among the deep-sea eels. The earliest fossil eels are known from the Late Cretaceous ( Cenomanian ) of Lebanon . These early eels retain primitive traits such as pelvic fins and thus do not appear to be closely related to any extant taxa. Body fossils of modern eels do not appear until the Eocene , although otoliths assignable to extant eel families and even some genera have been recovered from

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960-407: Is a simple system usually without gearing so that the vertical axle of the water wheel becomes the drive spindle of the mill. A stream wheel is a vertically mounted water wheel that is rotated by the water in a water course striking paddles or blades at the bottom of the wheel. This type of water wheel is the oldest type of horizontal axis wheel. They are also known as free surface wheels because

1040-713: Is a traditional Māori food in New Zealand . In Italian cuisine , eels from the Valli di Comacchio , a swampy zone along the Adriatic coast, are especially prized, along with freshwater eels of Bolsena Lake and pond eels from Cabras, Sardinia . In northern Germany , the Netherlands , the Czech Republic , Poland , Denmark , and Sweden , smoked eel is considered a delicacy . Elvers, often fried, were once

1120-599: Is an adjective form of an older word, ελλυ, meaning "snake", which is directly comparable to Hittite ellu-essar- "snake pit". This myth likely came to Greece via Anatolia. In the Hittite version of the myth, the dragon is called Illuyanka : the illuy- part is cognate to the word illa , and the -anka part is cognate to angu , a word for "snake". Since the words for "snake" (and similarly shaped animals) are often subject to taboo in many Indo-European (and non-Indo-European) languages, no unambiguous Proto-Indo-European form of

1200-597: 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. An episode from the Alexandrian War in 48 BC tells of how Caesar's enemies employed geared waterwheels to pour sea water from elevated places on the position of the trapped Romans. Around 300 AD, the noria was finally introduced when the wooden compartments were replaced with inexpensive ceramic pots that were tied to

1280-414: Is low in nutrients and rather cool. The crayfish , which has died out in most European waterbodies due to crayfish plague , has been able to survive in many Upper Harz Ponds thanks to their isolated locations. Pond operators and fishing leaseholders have worked successfully to increase their numbers. The operation of the ponds over many centuries with constantly changing levels of water has also created

1360-507: Is needed. Larger heads store more gravitational potential energy for the same amount of water so the reservoirs for overshot and backshot wheels tend to be smaller than for breast shot wheels. Overshot and pitchback water wheels are suitable where there is a small stream with a height difference of more than 2 metres (6.5 ft), often in association with a small reservoir. Breastshot and undershot wheels can be used on rivers or high volume flows with large reservoirs. A horizontal wheel with

1440-404: Is the only pond not grouted with grass turves, but with granite sand known as granitgrus and with a dam height of 21 m and reservoir volume of 1.7 million m³ of water stands head and shoulders above the other ponds in terms of size. Although these water features have been artificially created, rare flora and fauna have evolved in and around many of the Upper Harz ponds. The water

1520-408: Is the overhead timber structure and a branch to the left supplies water to the wheel. The water exits from under the wheel back into the stream. A special type of overshot/backshot wheel is the reversible water wheel. This has two sets of blades or buckets running in opposite directions so that it can turn in either direction depending on which side the water is directed. Reversible wheels were used in

1600-542: Is used as a metaphor for Nazi atrocities, and the sight of eels being killed by a fisherman triggers the madness of the protagonist's mother. Sinister implications of eels fishing are also referenced in Jo Nesbø 's Cockroaches , the second book of the Harry Hole detective series. The book's background includes a Norwegian village where eels in the nearby sea are rumored to feed on the corpses of drowned humans, making

1680-495: Is used for wheels where the water entry is significantly above the bottom and significantly below the top, typically the middle half. They are characterized by: Both kinetic (movement) and potential (height and weight) energy are utilised. The small clearance between the wheel and the masonry requires that a breastshot wheel has a good trash rack ('screen' in British English) to prevent debris from jamming between

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1760-481: The Ancient Near East before Alexander's conquest can be deduced from its pronounced absence from the otherwise rich oriental iconography on irrigation practices. Unlike other water-lifting devices and pumps of the period though, the invention of the compartmented wheel cannot be traced to any particular Hellenistic engineer and may have been made in the late 4th century BC in a rural context away from

1840-666: The Campanian and Maastrichtian , indicating some level of diversification among the extant groups prior to the Cretaceous-Paleogene extinction , which is also supported by phylogenetic divergence estimates. One of these otolith taxa, the mud-dwelling Pythonichthys arkansasensis , appears to have thrived in the aftermath of the K-Pg extinction, based on its abundance. Taxonomy based on Eschmeyer's Catalog of Fishes : Order Anguilliformes In some classifications,

1920-481: The European eel , Japanese eel , and American eel to its seafood red list. Japan consumes more than 70% of the global eel catch. The English name "eel" descends from Old English ǣl , Common Germanic *ēlaz . Also from the common Germanic are West Frisian iel , Dutch aal , German Aal , and Icelandic áll . Katz (1998) identifies a number of Indo-European cognates, among them

2000-640: The Hellenistic Greek world , Rome , China and India . Waterwheels saw continued use in the post-classical age , like in medieval Europe and the Islamic Golden Age , but also elsewhere. In the mid- to late 18th century John Smeaton 's scientific investigation of the water wheel led to significant increases in efficiency, supplying much-needed power for the Industrial Revolution . Water wheels began being displaced by

2080-517: The Lower Saxon part of the Harz. The barriers were built as earth-fill dams , the fill being usually excavated on site. Usually small quarries were established in the terrain earmarked as the future reservoir; this had the added advantage that it increased its eventual capacity. Neither clay nor silt could be used as grouting material because they did not occur in sufficient quantities in

2160-788: The Northeast . Freshwater eels, known as Kusia in Assamese , are eaten with curry, often with herbs. The European eel and other freshwater eels are mostly eaten in Europe and the United States , and is considered critically endangered. A traditional east London food is jellied eels , although the demand has significantly declined since World War II. The Spanish cuisine delicacy angulas consists of elver (young eels) sautéed in olive oil with garlic ; elvers usually reach prices of up to 1000 euro per kg. New Zealand longfin eel

2240-544: The copper mines at Rio Tinto in Spain , one system involving 16 such wheels stacked above one another so as to lift water about 80 feet from the mine sump. Part of such a wheel was found at Dolaucothi , a Roman gold mine in south Wales in the 1930s when the mine was briefly re-opened. It was found about 160 feet below the surface, so must have been part of a similar sequence as that discovered at Rio Tinto. It has recently been carbon dated to about 90 AD, and since

2320-414: The mining industry in order to power various means of ore conveyance. By changing the direction of the wheel, barrels or baskets of ore could be lifted up or lowered down a shaft or inclined plane. There was usually a cable drum or a chain basket on the axle of the wheel. It is essential that the wheel have braking equipment to be able to stop the wheel (known as a braking wheel). The oldest known drawing of

2400-431: The slender giant moray . Adults range in weight from 30 g (1 oz) to well over 25 kg (55 lb). They possess no pelvic fins , and many species also lack pectoral fins . The dorsal and anal fins are fused with the caudal fin, forming a single ribbon running along much of the length of the animal. Eels swim by generating waves that travel the length of their bodies. They can swim backward by reversing

2480-518: The Old English word for "hedgehog", which is igil (meaning "snake eater"), and perhaps in the egi- of Old High German egidehsa "wall lizard". According to this theory, the name Bellerophon ( Βελλεροφόντης , attested in a variant Ἐλλεροφόντης in Eustathius of Thessalonica ) is also related, translating to "the slayer of the serpent" ( ahihán ). In this theory, the ελλερο-

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2560-650: The Paleobiology Database: Freshwater eels ( unagi ) and marine eels ( conger eel , anago ) are commonly used in Japanese cuisine ; foods such as unadon and unajū are popular, but expensive. Eels are also very popular in Chinese cuisine , and are prepared in many different ways. Hong Kong eel prices have often reached 1000 HKD (128.86 US Dollars) per kg, and once exceeded 5000 HKD per kg. In India , eels are popularly eaten in

2640-444: The Upper Harz. The Upper Harz miners had, however, learned from experience that grass sods or turves made excellent grouting; by placing them one on top of another, in a similar fashion to building a wall, a layer of sods up to a metre thick would be built into the dam which ensured that it remained watertight. A wooden conduit ( Holzgerenne ) acted as a bottom outlet. It was usually made of oak due to its great durability. The valve

2720-469: The advantage that the bottom of the wheel is moving in the same direction as the water in the tailrace which makes it more efficient. It also performs better than an overshot wheel in flood conditions when the water level may submerge the bottom of the wheel. It will continue to rotate until the water in the wheel pit rises quite high on the wheel. This makes the technique particularly suitable for streams that experience significant variations in flow and reduces

2800-442: The bottom of a water-filled, circular shaft. The water from the mill-race which entered tangentially the pit created a swirling water column that made the fully submerged wheel act like true water turbines , the earliest known to date. Apart from its use in milling and water-raising, ancient engineers applied the paddled waterwheel for automatons and in navigation. Vitruvius (X 9.5–7) describes multi-geared paddle wheels working as

2880-400: The combination of the separate Greek inventions of the toothed gear and the waterwheel into one effective mechanical system for harnessing water power. Vitruvius' waterwheel is described as being 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). About the same time, the overshot wheel appears for the first time in

2960-413: The crayfish populations. The following list includes the majority of the dammed ponds built by the Upper Harz miners, where they are still in operation or where the dam ruins are still clearly visible. Mill ponds are not included. A total of 143 dams and former dams have been documented. (†) means: pond out of service, largely dry. Dam remains exist. Where no data is given, this usually indicates that

3040-411: The descendants of the water wheel, as they too take advantage of the movement of water downhill. Water wheels come in two basic designs: The latter can be subdivided according to where the water hits the wheel into backshot (pitch-back ), overshot, breastshot, undershot, and stream-wheels. The term undershot can refer to any wheel where the water passes under the wheel but it usually implies that

3120-516: The direction of the wave. Most eels live in the shallow waters of the ocean and burrow into sand, mud, or amongst rocks. Most eel species are nocturnal , and thus are rarely seen. Sometimes, they are seen living together in holes or "eel pits". Some eels also live in deeper water on the continental shelves and over the slopes deep as 4,000 m (13,000 ft). Only members of the Anguilla regularly inhabit fresh water, but they, too, return to

3200-402: The driving car. Water wheels were still in commercial use well into the 20th century, but they are no longer in common use today. Uses included milling flour in gristmills , grinding wood into pulp for papermaking , hammering wrought iron , machining, ore crushing and pounding fibre for use in the manufacture of cloth . Some water wheels are fed by water from a mill pond, which is formed when

3280-469: The early larval stage to the eventual adult stage and are usually predators . The term "eel" is also used for some other eel-shaped fish, such as electric eels (genus Electrophorus ), swamp eels (order Synbranchiformes ), and deep-sea spiny eels (family Notacanthidae). However, these other clades , with the exception of deep-sea spiny eels, whose order Notacanthiformes is the sister clade to true eels, evolved their eel-like shapes independently from

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3360-442: The eel fisheries at Ballisodare were greatly improved by the hanging of loosely plaited grass ladders over barriers, enabling elvers to ascend more easily. Several sets of classifications of eels exist; some, such as FishBase which divide eels into 20 families, whereas other classification systems such as ITIS and Systema Naturae 2000 include additional eel families, which are noted below. Genomic studies indicate that there

3440-443: The energy in the flow of water striking the wheel as measured by English civil engineer John Smeaton in the 18th century. More modern wheels have higher efficiencies. Stream wheels gain little or no advantage from the head, a difference in water level. Stream wheels mounted on floating platforms are often referred to as hip wheels and the mill as a ship mill . They were sometimes mounted immediately downstream from bridges where

3520-416: The exhausting labor of milling and grinding. The compartmented water wheel comes in two basic forms, the wheel with compartmented body ( Latin tympanum ) and the wheel with compartmented rim or a rim with separate, attached containers. The wheels could be either turned by men treading on its outside or by animals by means of a sakia gear. While the tympanum had a large discharge capacity, it could lift

3600-443: The existence of these plants in the waterbodies concerned. By other ponds there are meadow bogs ( Kleinseggenried ), which are rich in sedges , rushes and cottongrass and moss communities. The fish population is primarily influenced by the angling clubs that lease fishing rights and stock the ponds with fish. Only native species of fish are desired, although eel and catfish are excluded due to their incompatibility with

3680-918: The family Cyematidae of bobtail snipe eels is included in the Anguilliformes, but in the FishBase system that family is included in the order Saccopharyngiformes . The electric eel of South America is not a true eel but is a South American knifefish more closely related to the carps and catfishes . Phylogeny based on Johnson et al. 2012. Protanguillidae Synaphobranchidae Heterenchelyidae Myrocongridae Muraenidae [REDACTED] Chlopsidae Derichthyidae Nettastomatidae Congridae [REDACTED] Ophichthidae Muraenesocidae Moringuidae Eurypharyngidae Saccopharyngidae [REDACTED] Monognathidae Cyematidae [REDACTED] Nemichthyidae Serrivomeridae Anguillidae [REDACTED] Based on

3760-431: The flow restriction of the bridge piers increased the speed of the current. Historically they were very inefficient but major advances were made in the eighteenth century. An undershot wheel is a vertically mounted water wheel with a horizontal axle that is rotated by the water from a low weir striking the wheel in the bottom quarter. Most of the energy gain is from the movement of the water and comparatively little from

3840-420: The head. They are similar in operation and design to stream wheels. The term undershot is sometimes used with related but different meanings: This is the oldest type of vertical water wheel. The word breastshot is used in a variety of ways. Some authors restrict the term to wheels where the water enters at about the 10 o’clock position, others 9 o’clock, and others for a range of heights. In this article it

3920-422: The industrial revolution. A vertically mounted water wheel that is rotated by water entering buckets just past the top of the wheel is said to be overshot. The term is sometimes, erroneously, applied to backshot wheels, where the water goes down behind the wheel. A typical overshot wheel has the water channeled to the wheel at the top and slightly beyond the axle. The water collects in the buckets on that side of

4000-623: The kinetic energy of the water entering the wheel. They are suited to larger heads than the other type of wheel so they are ideally suited to hilly countries. However even the largest water wheel, the Laxey Wheel in the Isle of Man , only utilises a head of around 30 m (100 ft). The world's largest head turbines, Bieudron Hydroelectric Power Station in Switzerland , utilise about 1,869 m (6,132 ft). Overshot wheels require

4080-559: The late Warring States period (476-221 BC). It says that the waterwheel was invented by Zigong, a disciple of Confucius in the 5th century BC. By at least the 1st century AD, the Chinese of the Eastern Han Dynasty were using water wheels to crush grain 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

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4160-475: The metropolis of Alexandria. The earliest depiction of a compartmented wheel is from a tomb painting in Ptolemaic Egypt which dates to the 2nd century BC. It shows a pair of yoked oxen driving the wheel via a sakia gear, which is here for the first time attested, too. The Greek sakia gear system is already shown fully developed to the point that "modern Egyptian devices are virtually identical". It

4240-493: The outside of an open-framed wheel. The Romans used waterwheels extensively in mining projects, with enormous Roman-era waterwheels found in places like modern-day Spain . They were reverse overshot water-wheels designed for dewatering deep underground mines. Several such devices are described by Vitruvius , including the reverse overshot water-wheel and the Archimedean screw . Many were found during modern mining at

4320-475: The palace of the Pontian king Mithradates VI Eupator , but its exact construction cannot be gleaned from the text (XII, 3, 30 C 556). The first clear description of a geared watermill offers the late 1st century BC Roman architect Vitruvius who tells of the sakia gearing system as being applied to a watermill. Vitruvius's account is particularly valuable in that it shows how the watermill came about, namely by

4400-418: The pestle and mortar, which is so useful, and later on it was cleverly improved in 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. In

4480-410: The pond ended up in other hands before the mines closed and has not been precisely documented. Water wheel A water wheel is a machine for converting the energy of flowing or falling water into useful forms of power, often in a watermill . A water wheel consists of a wheel (usually constructed from wood or metal), with a number of blades or buckets arranged on the outside rim forming

4560-497: The rushing of the water ( chi shui ) to operate it ... Thus the people got great benefit for little labor. They found the 'water(-powered) bellows' convenient and adopted it widely. Water wheels in China found practical uses such as this, as well as extraordinary use. The Chinese inventor Zhang Heng (78–139) was the first in history to apply motive power in rotating the astronomical instrument of an armillary sphere , by use of

4640-426: The sea to breed. The heaviest true eel is the European conger . The maximum size of this species has been reported as reaching a length of 3 m (10 ft) and a weight of 110 kg (240 lb). Other eels are longer, but do not weigh as much, such as the slender giant moray , which reaches 4 m (13 ft). Eels begin life as flat and transparent larvae , called leptocephali . Eel larvae drift in

4720-508: The sea's surface waters, feeding on marine snow , small particles that float in the water. Eel larvae then metamorphose into glass eels and become elvers before finally seeking out their juvenile and adult habitats. Some individuals of anguillid elvers remains in brackish and marine areas close to coastlines, but most of them enter freshwater where they travel upstream and are forced to climb up obstructions, such as weirs , dam walls, and natural waterfalls. Gertrude Elizabeth Blood found that

4800-766: The second part of the Latin word for eels, anguilla , attested in its simplex form illa (in a glossary only), and the Greek word for "eel", egkhelys (the second part of which is attested in Hesychius as elyes ). The first compound member, anguis ("snake"), is cognate to other Indo-European words for "snake" (compare Old Irish escung "eel", Old High German unc "snake", Lithuanian angìs , Greek ophis, okhis , Vedic Sanskrit áhi , Avestan aži , Armenian auj, iž , Old Church Slavonic *ǫžь , all from Proto-Indo-European *h₁ogʷʰis ). The word also appears in

4880-478: The size, complexity, and hence cost of the tailrace. The direction of rotation of a backshot wheel is the same as that of a breastshot wheel but in other respects, it is very similar to the overshot wheel. See below. Some wheels are overshot at the top and backshot at the bottom thereby potentially combining the best features of both types. The photograph shows an example at Finch Foundry in Devon, UK. The head race

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4960-419: The smaller, less expensive and more efficient turbine , developed by Benoît Fourneyron , beginning with his first model in 1827. 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

5040-874: The town is located. The daylight passage in the spring of elvers upstream along the Thames was at one time called "eel fare". The word 'elver' is thought to be a corruption of "eel fare". A famous attraction on the French Polynesian island of Huahine (part of the Society Islands ) is the bridge across a stream hosting three- to six-foot-long eels, deemed sacred by local culture. Eel fishing in Nazi -era Danzig plays an important role in Günter Grass ' novel The Tin Drum . The cruelty of humans to eels

5120-437: The true eels. As a main rule, most eels are marine. Exceptions are the catadromous genus Anguilla and the freshwater moray , which spend most of their life in freshwater, the anadromous rice-paddy eel , which spawns in freshwater, and the freshwater snake eel Stictorhinus . Eels are elongated fish, ranging in length from 5 cm (2 in) in the one-jawed eel ( Monognathus ahlstromi ) to 4 m (13 ft) in

5200-457: The use of such wheels for submerging siege mines as a defensive measure against enemy sapping. 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). Several Greek papyri of the 3rd to 2nd century BC mention the use of these wheels, but do not give further details. The non-existence of the device in

5280-444: The usurpation of Wang Mang ), it states 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 of the mythological Fu Xi, a passage of his writing gives hint that the water wheel was in widespread use by the 1st century AD in China ( Wade-Giles spelling): Fu Hsi invented

5360-448: The vertical-axle waterwheel. In the 2nd century AD Barbegal watermill complex a series of sixteen 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". In Roman North Africa , several installations from around 300 AD were found where vertical-axle waterwheels fitted with angled blades were installed at

5440-400: The water entry is low on the wheel. Overshot and backshot water wheels are typically used where the available height difference is more than a couple of meters. Breastshot wheels are more suited to large flows with a moderate head . Undershot and stream wheel use large flows at little or no head. There is often an associated millpond , a reservoir for storing water and hence energy until it

5520-416: The water hits the wheel paddles, into overshot, breastshot and undershot wheels. The two main functions of waterwheels were historically water-lifting for irrigation purposes and milling, particularly of grain. In case of horizontal-axle mills, a system of gears is required for power transmission, which vertical-axle mills do not need. The earliest waterwheel working like a lever was described by Zhuangzi in

5600-434: The water is not constrained by millraces or wheel pits. Stream wheels are cheaper and simpler to build and have less of an environmental impact than other types of wheels. They do not constitute a major change of the river. Their disadvantages are their low efficiency, which means that they generate less power and can only be used where the flow rate is sufficient. A typical flat board undershot wheel uses about 20 percent of

5680-508: The water only to less than the height of its own radius and required a large torque for rotating. These constructional deficiencies were overcome by the wheel with a compartmented rim which was a less heavy design with a higher lift. The earliest literary reference to a water-driven, compartmented wheel appears in the technical treatise Pneumatica (chap. 61) of the Greek engineer Philo of Byzantium ( c.  280  – c.  220 BC ). In his Parasceuastica (91.43−44), Philo advises

5760-624: The wheel and the apron and potentially causing serious damage. Breastshot wheels are less efficient than overshot and backshot wheels but they can handle high flow rates and consequently high power. They are preferred for steady, high-volume flows such as are found on the Fall Line of the North American East Coast. Breastshot wheels are the most common type in the United States of America and are said to have powered

5840-406: The wheel, making it heavier than the other "empty" side. The weight turns the wheel, and the water flows out into the tail-water when the wheel rotates enough to invert the buckets. The overshot design is very efficient, it can achieve 90%, and does not require rapid flow. Nearly all of the energy is gained from the weight of water lowered to the tailrace although a small contribution may be made by

5920-449: The wood from which it was made is much older than the deep mine, it is likely that the deep workings were in operation perhaps 30–50 years after. It is clear from these examples of drainage wheels found in sealed underground galleries in widely separated locations that building water wheels was well within their capabilities, and such verticals water wheels commonly used for industrial purposes. Taking indirect evidence into account from

6000-554: The word for eel can be reconstructed. It may have been *ēl(l)-u- , *ēl(l)-o- , or something similar. The large lake of Almere , which existed in the early Medieval Netherlands , got its name from the eels which lived in its water (the Dutch word for eel is aal or ael , so: " ael mere " = "eel lake"). The name is preserved in the new city of Almere in Flevoland , given in 1984 in memory of this body of water on whose site

6080-510: The work of the Greek technician Apollonius of Perge , the British historian of technology M.J.T. Lewis dates 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. A watermill is reported by the Greek geographer Strabon ( c.  64 BC  – c.  AD 24 ) to have existed sometime before 71 BC in

6160-589: The year 31 AD, the engineer and Prefect of Nanyang , Du Shi (d. 38), applied a complex use of the water wheel and machinery to power the bellows of the blast furnace to create cast iron . Du Shi is mentioned briefly in the Book of 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 of Nanyang. He

6240-425: Was a generous man and his policies were peaceful; he destroyed evil-doers and established the dignity (of his office). Good at planning, he loved the common people and wished to save their labor. He invented a water-power reciprocator ( shui phai ) for the casting of (iron) agricultural implements. Those who smelted and cast already had the push-bellows to blow up their charcoal fires, and now they were instructed to use

6320-475: Was a so-called Striegel , which acted like a plug and closed off the inlet to the wooden channels and was operated by rods. Both grass sod grouting and wooden bottom outlets are still in use in many of the ponds. The dams themselves are between 4 and 15 m high and the impounded volumes varied between 10,000 and 600,000 m. One notable exception is the Oderteich northeast of Sankt Andreasberg , which

6400-490: Was later increased significantly through the use of additional collection ditches. Today the ponds are operated for several reasons: the protection of historic monuments , rural conservation , nature conservation and recreation . Several ponds also provide flood protection ; others are used to supply drinking water . The operator of the ponds today is the Harzwasserwerke , who also manage six modern dams in

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