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Grand Canal (China)

The Grand Canal is a system of interconnected canals linking various major rivers in North and East China, serving as an important waterborne transport infrastructure between the north and the south during Medieval and premodern China. It is the longest artificial waterway in the world and a UNESCO World Heritage Site.

The Grand Canal's main stem, known to the Chinese as the Jing–Hang Grand Canal, is thought to extend for 1776 km and is divided into 6 main subsections. The Jiangnan Canal runs from the Qiantang River at Hangzhou to the Yangtze River at Zhenjiang; the Inner Canal from the Yangtze at Yangzhou to the Huai River at Huai'an, which for centuries was also its junction with the former course of the Yellow River; the Middle Canal from Huai'an to the Nansi Lakes; the Lu Canal from the lakes past Jining and the present course of the Yellow River to the Wei River at Linqing; the Southern Canal from Linqing to the Hai River at Tianjin; and the Northern Canal from Tianjin to Tongzhou on the outskirts of Beijing. As such, it passes through the provinces and municipalities of Zhejiang, Jiangsu, Shandong, Hebei, Tianjin, and Beijing. In 2014, the Chinese government and UNESCO recognized the Eastern Zhejiang Canal from Hangzhou to Ningbo along the former Tongji and Yongji Canals as official components of the Grand Canal.

The oldest sections of what is now the Grand Canal were completed in the early 5th century BC during the conflicts of China's Spring and Autumn period to provide supplies and transport routes for the states of Wu and Yue. The network was completed by Emperor Yang of the Sui dynasty in AD 609, linking the fertile Jiangnan region in the south to his capital at Luoyang in the west and to his armies in the far north. His unsuccessful and unpopular wars and the massive amounts of conscripted labor involved in creating the canal were among the chief factors in the rapid fall of the Sui, but the connection of China's major watersheds and population centers proved enormously beneficial. Additional canals supplied Chang'an (now Xi'an) even further west under the Tang dynasty while stopover towns along the main course became the economic hubs of the empire. Periodic flooding of the Yellow River threatened the safety and functioning of the canal while, during wartime, the rivers' high dikes were sometimes deliberately broken to delay or sweep away advancing enemy troops. Even so, restoration and improvement of the canal and its associated flood control works was assumed as a duty by each successive dynasty. The canal played a major role in periodically reuniting northern and southern China, and officials in charge of the canal and nearby salt works grew enormously wealthy. Despite damage from floods, rebellions, and wars, the canal's importance only grew with the removal of the capital to Khanbaliq under the Mongol Yuan and to Beijing under Yongle Emperor of the Ming dynasty and the Manchu Qing dynasty. Despite the importance of railways and roads in modern China, the People's Republic of China has worked to improve the navigability of the canal since the end of the Chinese Civil War and the portion south of the Yellow River remains in heavy use by barges carrying bulk cargo. Increasing concern over pollution in China and particularly the use of the Grand Canal as the eastern path of the South-North Water Diversion Project—intended to provide clean potable water to the north—has led to regulations and several projects to improve water quality along the waterway.

The greatest height on the canal is an elevation of 42 m above sea level reached in the foothills of Shandong. Ships in Chinese canals did not have trouble reaching higher elevations after the Song official and engineer Qiao Weiyue invented the pound lock in the 10th century. The canal has been admired by many visitors throughout its history, including the Japanese monk Ennin (794–864), the Persian historian Rashid al-Din Hamadani (1247–1318), the Korean official Choe Bu (1454–1504), and the Italian missionary Matteo Ricci (1552–1610).

Early periods
In the late Spring and Autumn period, King Fuchai of Wu (whose capital was in present-day Suzhou), ventured north to attack the State of Qi. He ordered a canal to be constructed for trading purposes, as well as a means to ship ample supplies north in case his forces should engage the northern states of Song and Lu. This became known as the Han or Hangou Canal ( t 邗溝, s 邗沟, Hángōu). Work began in 486 BC, from south of Yangzhou to north of Huai'an in Jiangsu, and within three years the Han Canal had connected the Yangtze with the Huai River utilizing existing waterways, lakes, and marshes.

The Han Canal is known as the second oldest section of the later Grand Canal since the Hong Canal ( t, s , Hónggōu, "Canal of the Wild Geese" or "Far-Flung Canal") most likely preceded it. It linked the Yellow River near Kaifeng to the Si and Bian rivers and became the model for the shape of the Grand Canal in the north. The exact date of the Hong Canal's construction is uncertain; it is first mentioned by the diplomat Su Qin in 330 BC when discussing state boundaries. The historian Sima Qian (145–90 BC) knew of no historical date for it, placing his discussion of it just after the legendary works of Yu the Great; modern scholars now consider it to belong to the 6th century BC.

Sui dynasty

The reunification of China under the Sui dynasty (581–618) ended three centuries of chaos since the Upheaval of the Five Barbarians, and the renewed political stability allowed both the thorough repair of existing canals and flood control systems as well as the construction of new canals. The primary consideration of the Sui canals was the need to tap into the expanding economic and agricultural resources of the Jiangnan region in the southeast to enrich the main Sui capital at Luoyang to the west and to supply the expeditionary Sui armies in the Goguryeo-Sui Wars to the northeast. The institution of the Grand Canal also obviated the need for army garrisons to become self-sufficient part-time militia-farmers while guarding the dry frontiers between China, Goguryeo and Göktürk.

A dike-building project in 587 along the Yellow River—overseen by engineer Liang Rui—established canal lock gates to regulate water levels for the canal. Double slipways were installed to haul boats over when the difference in water levels was too great for the flash lock to operate. Similarly, by the year 600, there were major buildups of silt on the bottom of the Hong Canal, obstructing river barges whose drafts were too deep for its waters. The chief engineer of the Sui dynasty, Yuwen Kai, advised the digging of a new canal that would run parallel to the existing canal, diverging from it at Chenliu (Yanzhou). The new canal was to pass not Xuzhou but Suzhou, to avoid connecting with the Si River and instead make a direct connection with the Huai River just west of Lake Hongze. With the recorded labor of five million people under the supervision of Ma Shumou, the first major section of the Grand Canal was completed in the year 605 and was called the Bian Qu.

The Grand Canal was fully completed from the years 604 to 609 under Emperor Yang, first by linking his southern capital Yangzhou northwest to Luoyang by the Tongji Canal ( t, s , Tōngjì Qú). He then proceeded to connect Yangzhou southeast to Suzhou and Hangzhou by the Jiangnan Canal and to connect Luoyang northeast to his wars with Korea by the Yongji Canal ( t, s , Yǒngjì Qú). After this network's completion in 609, Emperor Yang was said to have led a flotilla of boats 105 km long from the north down to his southern capital at Yangzhou. This process again involved massive levies of conscripted labor and was detailed at length in the Record of the Opening of the Canal ( t 《》, s 《》, Kāihéjì).

At this point, the Grand Canal continued to use noncontiguous artificial channels and both canalized and natural waterways rather than presenting a single continuous manmade canal. However, running alongside and parallel to the course of the canals was an imperial roadway with stables maintained at regular intervals to support a rapid courier system. Enormous lines of trees were also planted along parts of the canal as windbreaks.

Tang to Yuan dynasties
Although the Tang dynasty (618–907) capital at Chang'an was the most thriving metropolis of China in its day, it was the city of Yangzhou—in proximity to the Grand Canal—that was the economic hub of the Tang era. Besides being the headquarters for the government salt monopoly and the largest pre-modern industrial production center of the empire, Yangzhou was also the geographical midpoint along the north–south trade axis, and so became the major center for southern goods shipped north. One of the greatest benefits of the canal system in the Tang dynasty—and subsequent dynasties—was that it reduced the cost of shipping grain that had been collected in taxes (caoyun) from the Yangtze Delta to northern China. Minor additions to the canal were made after the Sui period to cut down on travel time, but overall no fundamental differences existed between the Sui Grand Canal and the Tang Grand Canal.

By the year 735, it was recorded that about 149685400 kg of grain were shipped annually along the canal. The Tang government oversaw canal lock efficiency and built granaries along the route in case a flood or other disaster impeded the path of shipment. To ensure smooth travel of grain shipments, Transport Commissioner Liu Yan (in office from 763 to 779) had special river barge ships designed and constructed to fit the depths of each section of the entire canal.

After the An Lushan rebellion (755–763), the economy of North China was greatly damaged and never recovered due to wars and to constant flooding of the Yellow River. Such a case occurred in the year 858 when an enormous flood along the Grand Canal inundated thousands of acres of farmland and killed tens of thousands of people in the North China Plain. Such an unfortunate event could reduce the legitimacy of a ruling dynasty by causing others to perceive it as having lost the Mandate of Heaven; this was a good reason for dynastic authorities to maintain a smooth and efficient canal system.

The city of Kaifeng grew to be a major hub, later becoming the capital of the Song dynasty (960–1279). Although the Tang and Song dynasty international seaports—the greatest being Guangzhou and Quanzhou, respectively—and maritime foreign trade brought merchants great fortune, it was the Grand Canal within China that spurred the greatest amount of economic activity and commercial profit. During the Song and earlier periods, barge ships occasionally crashed and wrecked along the Shanyang Yundao section of the Grand Canal while passing the double slipways, and more often than not those were then robbed of the tax grain by local bandits. This prompted Qiao Weiyue, an Assistant Commissioner of Transport for Huainan, to invent a double-gate system known as the pound lock in the year 984. This allowed ships to wait within a gated space while the water could be drained to appropriate levels; the Chinese also built roofed hangars over the space to add further protection for the ships.

Much of the Grand Canal was ruined for several years after 1128 when Kaifeng's governor Du Chong (, Dù Chōng, d.1141) decided to break the dykes and dams holding back the waters of the Yellow River in order to decimate the oncoming Jurchen invaders during the Jin–Song wars. Over a series of floods, this entirely shifted the river south of Shandong, capturing the course of the Si River and emptying the Yellow River into Hongze Lake and the East China Sea for centuries. The Jurchen Jin dynasty continually battled with the Song in this region. The warfare led to the dilapidation of the canal until the Mongols invaded in the 13th century and began necessary repairs. During the Mongol Yuan dynasty (1271–1368) the capital of China was moved to Beijing, eliminating the need for the canal arm flowing west to Kaifeng or Luoyang. A summit section was dug across the foothills of the Shandong massif during the 1280s, shortening the overall length by as much as 700 km, making the total length about 1800 km and linking Hangzhou and Beijing with a direct north–south waterway for the first time. As in the Song and Jin era, the canal fell into disuse and dilapidation during the Yuan dynasty's decline.

The Grand Canal as infrastructure has had influence on other architectural works in the west. The Erie Canal in North America is designed and draws inspiration from the Chinese architecture. Many saw the canal as an economic advantage that could bring economic prosperity, like the canal and its benefits. Matteo Ricci's Journals describes the canal in great detail documenting the economic prosperity. The pound lock is one of the more notable features of the Erie canal that is directly connected to the infrastructure of the Grand Canal as it is used in other similar bodies of water.

Ming dynasty restoration
The Grand Canal was renovated almost in its entirety between 1411 and 1415 during the Ming dynasty (1368–1644). A magistrate of Jining, Shandong sent a memorandum to the throne of the Yongle Emperor protesting the current inefficient means of transporting 4,000,000 dan (428,000,000 liters) of grain a year by means of transferring it along several different rivers and canals in barge types that went from deep to shallow after the Huai River, and then transferred back onto deep barges once the shipment of grain reached the Yellow River. Chinese engineers built a dam to divert the Wen River to the southwest in order to feed 60% of its water north into the Grand Canal, with the remainder going south. They dug four large reservoirs in Shandong to regulate water levels, which allowed them to avoid pumping water from local sources and water tables. Between 1411 and 1415 a total of 165,000 laborers dredged the canal bed in Shandong and built new channels, embankments, and canal locks.

The Yongle Emperor moved the Ming capital from Nanjing to Beijing in 1403. This move deprived Nanjing of its status as chief political center of China. The reopening of the Grand Canal also benefited Suzhou over Nanjing since the former was in a better position on the main artery of the Grand Canal, and so it became Ming China's greatest economic center. The only other viable contender with Suzhou in the Jiangnan region was Hangzhou, but it was located 200 km further down the Grand Canal and away from the main delta. Even the shipwrecked Korean Choe Bu (1454–1504)—while traveling for five months throughout China in 1488—acknowledged that Hangzhou served not as a competitor but as an economic feeder into the greater Suzhou market. Therefore, the Grand Canal served to make or break the economic fortunes of certain cities along its route and served as the economic lifeline of indigenous trade within China.

The scholar Gu Yanwu of the early Qing dynasty (1644–1912) estimated that the previous Ming dynasty had to employ 47,004 full-time laborers recruited by the lijia corvée system in order to maintain the entire canal system. It is known that 121,500 soldiers and officers were needed simply to operate the 11,775 government grain barges in the mid-15th century.

Besides its function as a grain shipment route and major vein of river-borne indigenous trade in China, the Grand Canal had long been a government-operated courier route as well. In the Ming dynasty, official courier stations were placed at intervals of 35 to 45 km. Each courier station was assigned a different name, all of which were popularized in travel songs of the period.

Qing dynasty
The Manchus invaded China in the mid-17th century, allowed through the northern passes by the Chinese general Wu Sangui once the Ming capital at Beijing had fallen into the hands of a rebel army. The Manchus established the Qing dynasty (1644–1912), and under their leadership, the Grand Canal was overseen and maintained just as in earlier times.

In 1855, the Yellow River flooded and changed its course, severing the course of the canal in Shandong. This was foreseen by a Chinese official in 1447, who remarked that the flood-prone Yellow River made the Grand Canal like a throat that could be easily strangled (leading some officials to request restarting the grain shipments through the East China Sea). In 1855 the dikes of the canal were opened to flood advancing troops of the Taiping Rebellion's Northern Expedition.

Modern China
Because of various factors—the difficulty of crossing the Yellow River, the increased development of an alternative sea route for grain-ships, and the opening of the Tianjin-Pukou Railway and the Beijing-Hankou Railway—the canal languished and for decades the northern and southern parts remained separate. Many of the canal sections fell into disrepair, and some parts were returned to flat fields. Even today, the Grand Canal has not fully recovered its importance prior to the floods of the mid-19th century. After the founding of the People's Republic of China in 1949, the need for economic development led the authorities to order heavy reconstruction work.

The Grand Canal played a major role during Mao Zedong's Great Leap Forward as it provided an efficient way to transport grain. It was further refurbished following Deng Xiaoping's Reform and Opening Up, with improving economic conditions leading to greater infrastructure investment. The economic importance of the canal will likely continue. The provincial governments of Shandong, Jiangsu, and Zhejiang undertook dredging intended to increase shipping capacity by 40 percent by 2012. The central government has also made the main route of the Grand Canal the eastern path of the South-North Water Diversion Project, using enormous pumping stations to redirect water from the Yangtze Delta to the drier north.

The canal became greatly polluted during China's industrialization. By the 1990s, canal barge crews could tell when they neared Hangzhou by the stench of the visibly black water they passed through. Similarly, fishermen on Dongping Lake in Shandong objected to the introduction of water from the Yangtze as part of the South-North Water Diversion Project when they saw it noticeably killing fish and affecting their catch. During the 21st century, increasing efforts have been made to improve environmental conditions along the canal. Around Hangzhou, for instance, a $250 million restoration project begun in 2001 improved water quality to the point where it no longer produces a noticeable odor and is once again capable of supporting some fauna.

On 22 June 2014, UNESCO's Conference on World Heritage listed the Grand Canal as a World Heritage Site.

Historical sections
As well as its present-day course, fourteen centuries of canal-building have left the Grand Canal with a number of historical sections. Some of these have disappeared, others are still partially extant, and others form the basis for the modern canal. The following are the most important but do not form an exhaustive list.

Jia Canal
In 12 BC, in order to solve the problem of the Grand Canal having to use 160 km of the perilous course of the Yellow River in Northern Jiangsu, a man named Li Hualong created the Jia Canal. Named after the Jia River whose course it followed, it ran 140 km from Xiazhen (modern Weishan) on the shore of Shandong's Weishan Lake to Suqian in Jiangsu. The construction of the Jia Canal left only 100 km of Yellow River navigation on the Grand Canal, from Suqian to Huai'an, which by 1688 had been removed by the construction of the Middle Canal by Jin Fu.

Nanyang New Canal
In 1566, to escape the problems caused by flooding of the Yellow River around Yutai (now on the western shore of Weishan Lake), the Nanyang New Canal was opened. It ran for 75 km from Nanyang (now Nanyang Town, located in the center of Weishan Lake) to the small settlement of Liucheng (in the vicinity of modern Gaolou Village, Weishan County, Shandong) north of Xuzhou City. This change in effect moved the Grand Canal from the low-lying and flood-prone land west of Weishan Lake onto the marginally higher land to its east. It was fed by rivers flowing from east to west from the borders of the Shandong massif.

Huitong Canal
North of the Jizhou Canal summit section, the Huitong Canal ran downhill, fed principally by the River Wen, to join the Wei River in the city of Linqing. In 1289, a geological survey preceded its one-year construction. The Huitong Canal, built by an engineer called Ma Zhizhen, ran across sharply sloping ground and the high concentration of locks gave it the nicknames chahe or zhahe, i.e. 'the river of locks'. Its great number of feeder springs (between two and four hundred, depending on the counting method and season of the year) also led to it being called the quanhe or 'river of springs'.

Jizhou Canal
This, the Grand Canal's first true summit section, was engineered by the Mongol Oqruqči in 1238 to connect Jining to the southern end of the Huitong Canal. It rose to a height of 42 meters (138 ft) above the Yangtze, but environmental and technical factors left it with chronic water shortages until it was re-engineered in 1411 by Song Li of the Ming. Song Li's improvements, recommended by a local man named Bai Ying, included damming the rivers Wen and Guang and drawing lateral canals from them to feed reservoir lakes at the very summit, at a small town called Nanwang.

Duke Huan's Conduit
In AD 369, General Huan Wen of the Eastern Jin dynasty connected the shallow river valleys of the Huai and the Yellow. He achieved this by joining two of these rivers' tributaries, the Si and the Ji respectively, at their closest point, across a low watershed of the Shandong massif. Huan Wen's primitive summit canal became a model for the engineers of the Jizhou Canal.

Yilou Canal
The Shanyang Canal originally opened onto the Yangtze a short distance south of Yangzhou. As the north shore of the Yangtze gradually silted up to create the sandbank island of Guazhou, it became necessary for boats crossing to and from the Jiangnan Canal to sail the long way around the eastern edge of that island. After a particularly rough crossing of the Yangtze from Zhenjiang, the local prefect realized that a canal dug directly across Guazhou would reduce the journey time and thus make the crossing safer. The Yilou Canal was opened in 738 and still exists, though not as part of the modern Grand Canal route.

Modern course
The Grand Canal nominally runs between Beijing and Hangzhou over a total length of 1,794 km; however, only the section from Hangzhou to Liangshan County is currently navigable. Its course is today divided into seven sections. From south to north these are the Jiangnan Canal, the Li Canal, the Inner Canal, the Middle Canal, the Lu Canal, the South Canal, the North Canal, and the Tonghui River.

Man-Made Lake Lianhu

Training Lake "Lianhu" was used to feed water to the Grand Canal section near Jiangnan. Since the canal was man-made there was not enough naturally flowing water to keep the canal at proper depth so that boats could travel through it. So a man-made lake was used to feed water to the Jiangnan section of the Grand Canal. It was protected by the Government from reclamation and any use of the lake water without proper taxation was deemed illegal. It was supposed to be protected from profitable exploitation, but because the government changed over the years, lake Lianhu had been reclaimed many times and it started to become more shallow. The government changed the lake to become more profitable farmland which led to reclamations and agricultural irrigation using the lake. This began to lead to Lake Lianhu not being able to properly feed water to the Grand Canal. Loss of depth due to reclamation and maintenance costs became too high for the lake to become practical to use. Even though it was a man made lake it was still a beautiful sight. Many different people praised its beauty and various poems have been written about the lake. In recent years recreational uses for the lake have become more popular and may lead to the lake being restored.

Jiangnan Canal
This southernmost section of the canal runs from Hangzhou in Zhejiang, where the canal connects with the Qiantang River, to Zhenjiang in Jiangsu, where it meets the Yangtze. After leaving Hangzhou heading north toward Beijing, the canal passes around the eastern border of Lake Tai, through the major cities of Jiaxing, Suzhou, Wuxi, and Changzhou before reaching Zhenjiang. The Jiangnan (or 'South of the Yangtze') Canal is heavily utilized by barge traffic bringing coal, containers and construction materials to the booming delta. It is generally a minimum of 100 meters wide in the congested city centers, and often two or three times this width in the neighboring countryside. In recent years, broad bypass canals have been dug around the major cities to reduce 'traffic jams'.

The Suzhou section of the Jiangnan Canal flows through the western part of the city. It includes ten city gates and over 20 stone bridges of traditional design and historic areas that have been well preserved as well as temples and pavilions.

Inner Canal
The Inner Canal runs between the Yangtze and Huai rivers, skirting the Shaobo, Gaoyou, and Hongze lakes of central Jiangsu. This section connects the cities of Huai'an and Yangzhou. Here the land lying to the west of the canal is higher than its bed while the land to the east is lower. Historically the Shanghe region west of the canal has been prone to frequent flooding, while the Xiahe region to its east has been hit by less frequent but immensely damaging inundations caused by the failure of the Grand Canal levees. Recent works have allowed floodwaters from Shanghe to be diverted safely out to sea. Like the Jiangnan Canal, the Inner Canal is heavily utilized by barge traffic bringing coal, construction materials and increasingly shipping containers around Jiangsu Province.

Middle Canal
This 'Middle Canal' section runs from Huai'an to Weishan Lake, passing through Luoma Lake and following more than one course, the result of the impact of centuries of Yellow River flooding. After Pizhou, a northerly course passes through Tai'erzhuang to enter Weishan Lake at Hanzhuang bound for Nanyang and Jining (this course is the remnant of the New Nanyang Canal of 1566 – see below). A southerly course passes close by Xuzhou and enters Weishan Lake near Peixian. This latter course is less used today. Canal is utilized by barge traffic bringing coal and construction materials around northern Jiangsu Province.

Lu Canal
At Weishan Lake, both courses enter Shandong province. From here to Linqing, the canal is called the Lu or 'Shandong' Canal. It crosses a series of lakes—Zhaoyang, Dushan, and Nanyang—which nominally form a continuous body of water. At present, diversions of water mean that the lakes are often largely dry land. North of the northernmost Nanyang Lake is the city of Jining. Further on, about 30 km north of Jining, the highest elevation of the canal (38.5 m above sea level) is reached at the town of Nanwang. In the 1950s a new canal was dug to the south of the old summit section. The old summit section is now dry, while the new canal holds too little water to be navigable. About 50 km further north, passing close by Dongping Lake, the canal reaches the Yellow River. By this point waterless, it no longer connects to the river. It reappears again in Liaocheng City on the north bank where, intermittently flowing through a renovated stone channel, it reaches the city of Linqing on the Shandong – Hebei border. Liangshan County is the northern terminus of the canal for barge traffic.

Southern Canal
The fifth section of the canal extends for a distance of 524 km from Linqing to Tianjin along the course of the canalized Wei River. Though one of the northernmost sections, its name derives from its position relative to Tianjin. The Wei River at this point is heavily polluted while drought and industrial water extraction have left it too low to be navigable. The canal, now in Hebei province, passes through the cities of Dezhou and Cangzhou. Although to spectators, the canal appears to be a deep waterway in these city centers, its depth is maintained by weirs and the canal is all but dry where it passes through the surrounding countryside. At its terminus, the canal joins the Hai River in the center of Tianjin City before turning north-west.

Northern Canal and Tonghui River
In Tianjin, the canal heads northwest, for a short time following the course of the Yongding, a tributary of the Hai River, before branching off toward Tongzhou on the edge of the municipality of Beijing. It is here that the modern canal stops and that a Grand Canal Cultural Park has been built. During the Yuan dynasty, a further canal on the Tonghui River connected Tongzhou with a wharf called the Houhai or "rear sea" in central Beijing. In the Ming and Qing dynasties, however, the water level in the Tonghui River dropped and ships could not travel from Tongzhou to Beijing. Tongzhou then became the northern shipping terminus of the canal. Cargo was unloaded at Tongzhou and transported to Beijing by land. The Tonghui river still exists as a wide, concrete-lined storm-channel and drain for the suburbs of Beijing.

Eastern Zhejiang Canal
The Eastern Zhejiang Canal runs 239 km across the coastal plain south of Hangzhou Bay in northern Zhejiang. It begins at the Qiantang River in Xixing, Binjiang District, Hangzhou; crosses the Cao'e River in Shaoxing; and connects to the Yong River and ports on the East China Sea at Ningbo.

This Hangzhou–Ningbo canal began as the Shanyin Canal excavated in Shaoxing by the Yue official Fan Li in the early 5th century BC during China's Spring and Autumn period. Despite the difficulty of connecting the route's various watersheds, the present route was completed with the construction of the Xixing Canal by the Jin official He Xun in the late 3rd century AD. The canal was an important artery of transport and supply for the region during periods of disunity in medieval China and was particularly prosperous and vital during the Southern Song, who established their capital at Lin'an within present-day Hangzhou. During the Yuan, Ming, and Qing, the canal diminished in importance but was kept navigable until the development of railways and roads in the 19th and 20th century. Renovation of the canal for use by modern barges began in 2002, was completed except for areas around Ningbo by 2009, and was fully completed in late 2013.

In November 2008, the Eastern Zhejiang Canal was added to the Grand Canal's UNESCO nomination and, in May 2013, was officially included as part of the Grand Canal and listed among the 7th group of Major Historical and Cultural Sites Protected at the National Level by the Chinese government. In 2014, it was included with the Beijing–Hangzhou and Sui and Tang canals as part of UNESCO's listing for the Grand Canal.

Registered Sections and Sites of the World Heritage complex
The Grand Canal World Heritage site is composed of 31 sections and a number of accessory heritage sites.

Elevations
Though the canal nominally crosses the watersheds of five river systems, in reality, the variation between these is so low that it has only a single summit section. The elevation of the canal bed varies from 1 m below sea level at Hangzhou to 38.5 m above at its summit. At Beijing, it reaches 27 m, fed by streams flowing downhill from the mountains to the west. The water flows from Beijing toward Tianjin, from Nanwang north toward Tianjin, and from Nanwang south toward Yangzhou. The water level in the Jiangnan Canal remains scarcely above sea level (the Zhenjiang ridge is 12 meters higher than that of the Yangtze River).

Transportation

From the Tang to Qing dynasties, the Grand Canal served as the main artery between northern and southern China and was essential for the transport of grain to Beijing. Although it was mainly used for shipping grain, it also transported other commodities and the corridor along the canal developed into an important economic belt. Records show that, at its height, every year more than 8,000 boats transported four to six million dan (240,000–360,000 metric tons) of grain. The convenience of transport also enabled rulers to lead inspection tours to southern China. In the Qing dynasty, the Kangxi and Qianlong emperors made twelve trips to the south, on all occasions but one reaching Hangzhou.

The Grand Canal also enabled cultural exchange and political integration to occur between the north and south of China. The canal even made a distinct impression on some of China's early European visitors. Marco Polo recounted the Grand Canal's arched bridges as well as the warehouses and prosperous trade of its cities in the 13th century. The famous Roman Catholic missionary Matteo Ricci traveled from Nanjing to Beijing along the canal at the end of the 16th century.

Since the founding of the People's Republic of China in 1949, the canal has been used primarily to transport vast amounts of bulk goods such as bricks, gravel, sand, diesel, and coal. The Jianbi ship locks on the Yangtze are currently handling some 75,000,000 metric tons each year, and the Li Canal is forecast to reach 100,000,000 metric tons in the next few years. When first constructed, the canal served as a major source of transportation, linking northern and southern China. With the introduction of expressways, railways and high speed railways in modern China, passenger travel on the canal became far less common.

Currently, ships can only travel up to Jining. The section from Jining to Beijing is not available for transport due to the silt deposit buildup from the Yellow River and lack of water sources. There are plans for restoring transportation up to Tai'an.

South-North Water Transfer Project
The Grand Canal has been upgraded to serve as the Eastern Route of the South-North Water Transfer Project. Additional water is pumped into the canal from the Yangtze at Jiangdu near Yangzhou using a 400 m3/s pumping station. and repumped through 23 stations until it reaches the watershed at Nanwang. Afterwards the water flows by gravity, one secondary canal going to the Shandong peninsula, and the main canal bypasses the Yellow River through 7.9 km tunnels and flows through a modified route into reservoirs in Tianjin. The extra waterflow has allowed the start of several projects to reestablish shipping in the northern half of the Grand Canal.

Notable travelers
In 1169, with China divided between the Jurchen-led Jin dynasty in the north and the Southern Song dynasty in the south, the Southern Song Emperor Xiaozong sent a delegation to the Jurchen to wish their ruler well for the New Year. A scholar-official named Lou Yue, secretary to the delegation, recorded the journey, much of which was made upon the Grand Canal, and submitted his Diary of a Journey to the North to the emperor on his return.

In 1170, the poet, politician, and historian Lu You traveled along the Grand Canal from Shaoxing to the river Yangtze, recording his progress in a diary.

In the late 1200s, Marco Polo traveled extensively through China and his trips included time on the Grand Canal, then a major artery for shipping silk, porcelain, and wine.

In 1345, Maghrebi traveler Ibn Battuta traveled China and journeyed through the Abe Hayat river (Grand Canal) up to the capital Khanbalik (Beijing).

In 1488, the shipwrecked Korean scholar Choe Bu traveled the entire length of the Grand Canal on his way from Zhejiang to Beijing (and on to Korea) and left a detailed account of his trip.

In 1600, Matteo Ricci traveled to Beijing from Nanjing via the Grand Canal waterway to gain the support of the Wanli Emperor of the Ming dynasty with the help of Wang Zhongde, the Director of the Board of Rites in the central government of China at the time.

In 1793, after a largely fruitless diplomatic mission to Jehol, a large part of Lord Macartney's embassy returned south to the Yangtze delta via the Grand Canal.

In 1848, Robert Fortune reached Hang Chow Foo by the Grand Canal in his quest for tea plants.

title: Grand Canal (China)


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Arcade video game

An arcade video game takes player input from its controls, processes it through electrical or computerized components, and displays output to an electronic monitor or similar display. All arcade video games are coin-operated or accept other means of payment, housed in an arcade cabinet, and located in amusement arcades alongside other kinds of arcade games. Until the early 2000s, arcade video games were the largest and most technologically advanced segment of the video game industry.

Early prototypical entries Galaxy Game and Computer Space in 1971 established the principle operations for arcade games, and Atari's Pong in 1972 is recognized as the first successful commercial arcade video game. Improvements in computer technology and gameplay design led to a golden age of arcade video games, the exact dates of which are debated but range from the late 1970s to the early 1980s. This golden age includes Space Invaders, Pac-Man, and Donkey Kong. The arcade industry had a resurgence from the early 1990s to mid-2000s, including Street Fighter II, Mortal Kombat, and Dance Dance Revolution, but ultimately declined in the Western world as competing home video game consoles such as the Sony PlayStation and Microsoft Xbox increased in their graphics and gameplay capability and decreased in cost. Nevertheless, Japan, China, and South Korea retain a strong arcade industry in the present day.

History
Games of skill were popular amusement-park midway attractions from the 19th century on. With the introduction of electricity and coin-operated machines, they facilitated a viable business. When pinball machines with electric lights and displays were introduced in 1933 (but without the user-controller flippers which would not be invented until 1947) these machines were seen as games of luck. Numerous states and cities treated them as amoral playthings for rebellious young people, and banned them into the 1960s and 1970s.

Electro-mechanical games (EM games) appeared in arcades in the mid-20th century. Following Sega's EM game Periscope (1966), the arcade industry experienced a "technological renaissance" driven by "audio-visual" EM novelty games, establishing the arcades as a suitable environment for the introduction of commercial video games in the early 1970s. In the late 1960s, college student Nolan Bushnell had a part-time job at an arcade where he became familiar with EM games such as Chicago Coin's racing game Speedway (1969), watching customers play and helping to maintain the machinery, while learning the game business.

The early mainframe game Spacewar! (1962) inspired the first commercial arcade video game, Computer Space (1971), created by Nolan Bushnell and Ted Dabney and released by Nutting Associates. It was demonstrated at the Amusement & Music Operators Association (AMOA) show in October 1971. Another Spacewar-inspired coin-operated video game, Galaxy Game, was demonstrated at Stanford University in November 1971. Bushnell and Dabney followed their Computer Space success to create - with the help of Allan Alcorn - a table-tennis game, Pong, released in 1972. Pong became a commercial success, leading numerous other coin-op manufacturers to enter the market.

The video game industry transitioned from discrete integrated circuitry to programmable microprocessors in the mid-1970s, starting with Gun Fight in 1975. The arcade industry entered a "Golden Age" in 1978 with the release of Taito's Space Invaders, which introduced many novel gameplay features - including a scoreboard. From 1978 to 1982, several other major arcade-games from Namco, Atari, Williams Electronics, Stern Electronics, and Nintendo were all considered blockbusters, particularly Namco's Pac-Man (1980), which became a fixture in popular culture. Across North America and Japan, dedicated video-game arcades appeared and arcade-game cabinets appeared in many smaller storefronts. By 1981, the arcade video-game industry was worth US$8 billion in the US.

The novelty of arcade games waned sharply after 1982 due to several factors, including market saturation of arcades and arcade games, a moral panic over video games (similar to fears raised over pinball machines in the decades prior), and the 1983 video game crash as the home-console market impacted arcades. The arcade market had recovered by 1986, with the help of software-conversion kits, the arrival of popular beat 'em up games (such as Kung-Fu Master (1984) and Renegade (1986-1987)), and advanced motion simulator games (such as Sega's "taikan" games including Hang-On (1985), Space Harrier (1985), and Out Run (1986)). However, the growth of home video-game systems such as the Nintendo Entertainment System led to another brief arcade decline toward the end of the 1980s.

Arcade games continued to improve with the development of technology and of gameplay. In the early 1990s, the release of Capcom's Street Fighter II established the modern style of fighting games and led to a number of similar games such as Mortal Kombat, Fatal Fury, Killer Instinct, Virtua Fighter, and Tekken, creating a new renaissance in the arcades. Another factor was realism, including the "3D Revolution" from 2D and pseudo-3D graphics to "true" real-time 3D polygon graphics. This was largely driven by a technological arms-race between Sega and Namco. During the early 1990s games such as Sega's Virtua Racing and Virtua Fighter popularized 3D-polygon technology in arcades. 3D graphics later became popular in console and computer games by the mid-1990s, though arcade systems such as the Sega Model 3 remained considerably more advanced than home systems in the late 1990s. Until about 1996, arcade video-games had remained the largest segment of the global video-game industry. Arcades declined in the late 1990s, surpassed by the console market for the first time around 1997–1998.

Since the 2000s, arcade games have taken different routes globally. In the United States, arcades have become niche markets as they compete with the home-console market, and they have adapted other business models, such as providing other entertainment options or adding prize redemptions. In Japan, where arcades continue to flourish, games like Dance Dance Revolution and The House of the Dead aim to deliver tailored experiences that players cannot easily have at home.

Technology

Virtually all modern arcade games (other than the very traditional fair midway) make extensive use of solid state electronics, integrated circuits, and monitor screens, all installed inside an arcade cabinet.

With the exception of Galaxy Game and Computer Space, which were built around small form-factor mainframe computers, the first arcade games are based on combinations of multiple discrete logic chips, such as transistor–transistor logic (TTL) chips. Designing an arcade game was more about the combination of these TTL chips and other electronic components to achieve the desired effect on screen. More complex gameplay required significantly more TTL components to achieve this result. By the mid-1970s, the first inexpensive programmable microprocessors had arrived on the market. The first microprocessor-based video game is Midway's Gun Fight in 1975 (a conversion of Taito's Western Gun), and with the advent of Space Invaders and the golden era, microprocessor-based games became typical. Early arcade games were also designed around raster graphics displayed on a cathode-ray tube (CRT) display. Many games of the late 1970s and early 1980s use special displays that rendered vector graphics, though these waned by the mid-1980s as display technology on CRTs improved. Prior to the availability of color CRT or vector displays, some arcade cabinets have a combination of angled monitor positioning, one-way mirrors, and clear overlays to simulate colors and other graphics onto the gameplay field.

Coin-operated arcade video games from the 1990s to the 2000s generally use custom hardware often with multiple CPUs, highly specialized sound and graphics chips, and the latest in expensive computer graphics display technology. This allows more complex graphics and sound than contemporary video game consoles or personal computers. Many arcade games since the 2000s run on modified video game console hardware (such as the Sega NAOMI or Triforce) or gaming PC components (such as the Taito Type X). Many arcade games have more immersive and realistic game controls than PC or console games. This includes specialized ambiance or control accessories such as fully enclosed dynamic cabinets with force feedback controls, dedicated lightguns, rear-projection displays, reproductions of automobile or airplane cockpits, motorcycle or horse-shaped controllers, or highly dedicated controllers such as dancing mats and fishing rods. These accessories are usually too bulky, expensive, and specialized to be used with typical home PCs and consoles. Arcade makers experiment with virtual reality technology. Arcades have progressed from using coins as credits to smart cards that hold the virtual currency of credits.

Modern arcade cabinets use flat panel displays instead of cathode-ray tubes. Internet services such as ALL.Net, NESiCAxLive, e-Amusement and NESYS, allow the cabinets to download updates or new games, do online multiplayer gameplay, save progress, unlock content, or earn credits.

Genres
Many arcade games have short levels, simple and intuitive control schemes, and rapidly increasing difficulty. The classic formula for a successful arcade video game is "easy to learn, difficult to master" along with a "multiple life, progressively difficult level" paradigm. This is due to the environment of the arcade, where the player is essentially renting the game for as long as their in-game avatar can stay alive or until they run out of tokens. Games on consoles or PCs can be referred to as "arcade games" if they share these qualities, or are direct ports of arcade games.

Arcade racing games often have sophisticated motion simulator arcade cabinets, a simplified physics engine, and short learning time when compared with more realistic racing simulations. Cars can turn sharply without braking or understeer, and the AI rivals are sometimes programmed so they are always near the player with a rubberband effect. Other types of arcade-style games include music games (particularly rhythm games), and mobile and casual games with intuitive controls and short sessions.

Action
The term "arcade game" can refer to an action video game designed to play similarly to an arcade game with frantic, addictive gameplay. The focus of arcade action games is on the user's reflexes, and many feature very little puzzle-solving, complex thinking, or strategy skills. These include fighting games often played with an arcade controller, beat 'em up games including fast-paced hack and slash games, and light gun rail shooters and "bullet hell" shooters with intuitive controls and rapidly increasing difficulty.

Many arcade combat flight simulation games have sophisticated hydraulic motion simulator cabinets, and simplified physics and handling. Arcade flight games are meant to have an easy learning curve, in order to preserve their action component. Increasing numbers of console flight video games, such as Crimson Skies, Ace Combat, and Secret Weapons Over Normandy indicate the falling of manual-heavy flight sim popularity in favor of instant arcade flight action.

A modern subgenre of action games called "hack and slash" or "character action games" represent an evolution of traditional arcade action games, and are sometimes considered a subgenre of beat 'em up brawlers. This subgenre of games was largely defined by Hideki Kamiya, creator of the Devil May Cry and Bayonetta franchises.

Industry
Arcade games are found in restaurants, bowling alleys, college campuses, video rental shops, dormitories, laundromats, movie theaters, supermarkets, shopping malls, airports, and other retail environments. They are popular in public places where people are likely to have free time.

Their profitability is expanded by the popularity of conversions of arcade games for home-based platforms. In 1997, WMS Industries (parent company of Midway Games) reported that if more than 5,000 arcade units are sold, at least 100,000 home version units will be sold.

The American Amusement Machine Association (AAMA) is a trade association established in 1981 that represents the American coin-operated amusement machine industry, including 120 arcade game distributors and manufacturers. The Japan Amusement Machine and Marketing Association (JAMMA) represents the Japanese arcade industry. Arcade machines may have standardized connectors or interfaces such as JAMMA, or JVS, that help with quick replacement of game systems or boards in arcade cabinets. The game boards or arcade boards may themselves allow for games to be replaced via game cartridges or discs.

Conversions, emulators, and recreations
Prior to the 2000s, successful video games were often converted to a home video game console or home computer. Many of the initial Atari VCS games, for example, were conversions of Atari's success arcade games. Arcade game manufacturers that were not in the home console or computer business found licensing of their games to console manufacturers to be a successful business model, as console manufacturer competitors would vie for rights to more popular games. Coleco famously bested Atari to secure the rights to convert Nintendo's Donkey Kong, which it subsequently included as a pack-in game for the ColecoVision to challenge the VCS.

Arcade conversions typically had to make concessions for the lower computational power and capabilities of the home console, such as limited graphics or alterations in gameplay. Such conversions had mixed results. The Atari VCS conversion of Space Invaders was considered the VCS's killer application, helping to quadruple the VCS sales in 1980. In contrast, the VCS conversion of Pac-Man in 1982 was highly criticized for technical flaws due to VCS limitations such as flickering ghosts and simplified gameplay. Though Pac-Man was the best-selling game on the VCS, it eroded consumer confidence in Atari's games and partially contributed to the 1983 crash.

The need for arcade conversions began to wane as arcade game manufacturers like Nintendo, Sega, and SNK entered the home console market and used similar technology within their home consoles as found at the arcade, negating the need to simplify the game. Concessions still may be made for a home release; notably, the Super Nintendo Entertainment System conversion of Mortal Kombat removed much of the gore from the arcade version to meet Nintendo's quality control standards.

Exact copies of arcade video games can be run through emulators such as MAME on modern devices. An emulator is an application that translates foreign software onto a modern system, in real-time. Emulated games appeared legally and commercially on the Macintosh in 1994 with Williams floppy disks, Sony PlayStation in 1996, and Sega Saturn in 1997 with CD-ROM compilations such as Williams Arcade's Greatest Hits and Arcade's Greatest Hits: The Atari Collection 1, and on the PlayStation 2 and GameCube with DVD-ROM compilations such as Midway Arcade Treasures. Arcade games are downloaded and emulated through the Nintendo Wii Virtual Console service starting in 2009.

Using emulation, companies like Arcade1Up have produced at-scale or reduced-scale recreations of arcade cabinets using modern technology, such as LCD monitors and lightweight construction. These cabinets are typically designed to resemble the original arcade game cabinets, but may also support multiple related games. These cabinets can be offered in diverse and miniaturized styles, such as table-mounted and wall-mounted versions.

Highest-grossing
For arcade games, success is usually judged by either the number of arcade hardware units sold to operators, or the amount of revenue generated. The revenue can include the coin drop earnings from coins (such as quarters, dollars, or 100 yen coins) inserted into machines, and/or the earnings from hardware sales with each unit costing thousands of dollars. Most of the revenue figures listed below are incomplete as they only include hardware sales revenue, due to a lack of available data for coin drop earnings which typically account for the majority of a hit arcade game's gross revenue. This list only includes arcade games that either sold more than 10,000 hardware units or generated a revenue of more than US$10 million. Most of the games listed were released between the golden age of arcade video games (1978–1984) and the 1990s.

Franchises
These are the combined hardware sales of at least two or more arcade games that are part of the same franchise. This list only includes franchises that have sold at least 5,000 hardware units or grossed at least $10 million revenues.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Arcade video game


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Otto von Guericke

Otto von Guericke (, , ; spelled Gericke until 1666; 30 November 1602 – 21 May 1686) was a German scientist, inventor, mathematician and physicist. His pioneering scientific work, the development of experimental methods and repeatable demonstrations on the physics of the vacuum, atmospheric pressure, electrostatic repulsion, his advocacy for the reality of "action at a distance" and of "absolute space" were noteworthy contributions for the advancement of the Scientific Revolution.

Von Guericke was a very pious man in the Dionysian tradition and attributed the vacuum of space to the creations and designs of an infinite divinity. Von Guericke described this duality "as something that 'contains all things' and is 'more precious than gold, without beginning and end, more joyous than the perception of bountiful light' and 'comparable to the heavens'."

Early life and education
Otto von Guericke was born to a patrician family of Magdeburg. He was privately tutored until the age of fifteen. In 1617 he began studying law and philosophy at the Leipzig University. However, in 1620 his studies were disrupted by his father's death. He briefly returned home before continuing his studies at the Academia Julia in Helmstedt and the universities of Jena and Leiden. It was at Leiden that he first attended courses on mathematics, physics and military engineering. He concluded his academic education with a nine-month Grand Tour to France and England.

Family
Upon his return to Magdeburg in 1626 he married Margarethe Alemann, with whom he had three children (Anna Catherine, Hans Otto, and Jacob Christopher) before her untimely death in 1645. Anna Catherine and Jacob Christopher both died in infancy and in 1652 von Guericke married Dorothea Lentke.

Political career
Von Guericke was the offspring of one of Magdeburg's leading patrician families, that were well educated and well connected. His father and grandfather had been life-long members of the city council and at various occasions during their careers been appointed to serve as mayor of the city. In 1626, Otto von Guericke started his career as political representative of Magdeburg and accepted an official appointment to join the city council. However, in 1618, the Thirty Years' War had broken out. This exceptionally long, tragic and destructive conflict would soon also descend upon Magdeburg. Only a few years later, he had luckily fled from the city before an army of the imperial Catholic League, led by the Count of Tilly had completely surrounded and cut off Magdeburg. The attack culminated in the single most devastating event of the entire war, namely the Sack of Magdeburg. In May 1631, the imperial troops had crushed the city walls and indiscriminately plundered the riches. Around eighty percent of its more than 25,000 inhabitants perished. The material loss was also unusually high as widespread fires destroyed about 1,700 of a total of 1,900 buildings, including all of von Guericke's personal property. He returned to Magdeburg in 1631 and his academic engineer education designated him an appointee of the reconstruction committee.

He became a master brewer in an attempt to speedily acquire a new personal fortune and accumulate wealth for the city. In 1646, he was elected as Magdeburg's Burgomeister, the city's chief magistrate or executive, an office that arguably bestowed more power (in a practical sense) than that of a mayor. He held this position until his retirement in 1678. During four decades in office he undertook numerous diplomatic missions, which took him to many European courts and councils, where he met powerful executives and secretaries and addressed the illustrious elite of dukes, kings and emperors. In 1666, Otto von Guericke was ennobled by emperor Leopold I, which, apart from entitling him to add the "von" prefix to his name, was of little consequence. He also altered the spelling of his last name from "Gericke" to "Guericke".

Diplomatic pursuits
Otto von Guericke's first diplomatic mission on behalf of the city led him in September 1642 to the court of the Elector of Saxony at Dresden. Von Guericke's mandate was to bring about a more lenient treatment from the Saxon military commander for Magdeburg. In 1648, he represented the city at the peace treaty delegation, that ended the Thirty Year's War. During a 1654 diplomatic mission to Regensburg, Guericke presented his invention of the air-pump to impress those he was going to meet and help sway the talks in his favour, as well as promote his own scientific achievements. Diplomacy assignments, often dangerous as well as tedious, would occupy much of his time for the next twenty years. His private life, of which much remains unclear, was developing in parallel. Otto von Guericke utilised both his official status and his scientific knowledge in each other's support to serve his city's political agenda. Demonstrations of his inventions, such as the air-pump and the electrostatic generator were meant to impress his audiences and improve and extend political communication. He would, if necessary forgo scientific and technical elaborations on how his showpieces worked, leaving people to believe in his wizardry, a characteristic that was of great use for the promotion of a great leader.

Initial scientific investigations
Curious and inspired by the Copernican cosmology and hardly understanding new ideas of vast, endless, empty space where light would propagate, bodies of matter could move about unhindered, and sound cannot be detected, von Guericke set about replicating this nothing phenomenon on Earth. Von Guericke first started investigating the concept of a vacuum through the use of fire pumps by pumping water out of wooden barrels. However, he soon realised that the porosity of wood was allowing unwanted water, filled with dissolved air, to enter. The pressure fluctuations experienced inside the barrel were allowing this encapsulated air to escape: spoiling the vacuum inside. In 1647 he turned his focus to pumping out enclosed air instead of water to solve this problem.

Merging of his scientific and political careers

His scientific and diplomatic pursuits finally intersected when, at the Reichstag in Ratisbon in 1654, he was invited to demonstrate his experiments on the vacuum before the highest dignitaries of the Holy Roman Empire. He built a vacuum pump, pumped air out of two joined Magdeburg hemispheres, attached a team of horses to each side, and had them pull. He demonstrated this again to the King of Prussia in 1663 and was awarded a lifetime pension. One of these dignitaries, the Archbishop Elector Johann Philipp von Schönborn, bought von Guericke's apparatus from him and had it sent to his Jesuit College at Würzburg. One of the professors at the College, Fr. Gaspar Schott, entered into friendly correspondence with von Guericke and thus it was that, at the age of 55, von Guericke's work was first published as an Appendix to a book by Fr. Schott – Mechanica Hydraulico-pneumatica – published in 1657. This book came to the attention of Robert Boyle who, stimulated by it, embarked on his own experiments on air pressure and the vacuum, and in 1660 published New Experiments Physico-Mechanical touching the Spring of Air and its Effects. The following year this was translated into Latin and, made aware of it in correspondence with Fr. Schott, von Guericke acquired a copy. In the decade following the first publication of his own work von Guericke, in addition to his diplomatic and administrative commitments, was scientifically very active. He embarked upon his Magnum Opus — Ottonis de Guericke Experimenta Nova (ut vocantur) Magdeburgica de Vacuo Spatio — which as well as a detailed account of his experiments on the vacuum, contains his pioneering electrostatic experiments in which electrostatic repulsion was demonstrated for the first time and he sets out his theologically based view of the nature of space, but there are also contemporary arguments that he did not conceptualise these demonstrations as electrical. In the Preface to the Reader he claims to have finished the book on March 14, 1663, though publication was delayed for another nine years until 1672. In 1664, his work again appeared in print, again through the good offices of Gaspar Schott, the first section of whose book Technica Curiosa, titled Mirabilia Magdeburgica, was dedicated to von Guericke's work. The earliest reference to the celebrated Magdeburg hemispheres experiment is on page 39 of the Technica Curiosa, where Schott notes that von Guericke had mentioned them in a letter of July 22, 1656. Schott goes on to quote a subsequent letter of von Guericke of August 4, 1657, in which he states that he now had carried out the experiment, at considerable cost, with 12 horses.

The 1660s marked the ultimate end for the Magdeburg citizen's hope of achieving Free Imperial City status, a goal to which von Guericke had devoted some twenty years of diplomatic effort. On behalf of Magdeburg, he was the first signatory to the Treaty of Klosterberg in 1666 whereby Magdeburg accepted a garrison of Brandenburg troops (upon the withdrawal of the imperial garrison) and the obligation to pay dues to the Great Elector, Friedrich Wilhelm I of Brandenburg. Despite the Elector's crushing of Magdeburg's political aspirations, the personal relationship of von Guericke and Friedrich Wilhelm remained warm. The Great Elector was a patron of scientific scholarship. He had employed von Guericke's son, Hans Otto, as his resident in Hamburg and in 1666 had called Otto himself to the Brandenburg Rat. When the Experimenta Nova finally appeared it was prefaced with a dedication to Friedrich Wilhelm.

Later years
In 1677 von Guericke was reluctantly permitted to step down from his civic responsibilities, after repeated requests. In January 1681, as a precaution against an outbreak of the plague then threatening Magdeburg, he and his second wife Dorothea moved to Hamburg, where their son Hans Otto lived. There von Guericke died peacefully on May 11 (Julian) 1686, to the day 55 years after he had fled the siege in 1631. His body was returned to Magdeburg for interment in the Ulrichskirche on May 23 (Julian). The Otto von Guericke University Magdeburg was named in his honour.

Primary publications
There are three bodies of text, that contain systematic treatises on von Guericke's scientific work. The scientific studies and related experiments contained in the above works may be grouped under three topics, to each of which the following books of Experimenta Nova are dedicated:
 * 1. Friar Gaspar Schott's 1657 work Mechanica Hydraulico-pneumatica, originally intended as a brief guide to the hydraulic and pneumatic instruments in Athanasius Kircher's Roman museum, an appendix added by Schott, is a detailed account of Guericke's experiments on vacuums.
 * 2. Friar Gaspar Schott's 1664 Technica Curiosa, with appendix that contains a reupload of the 1657 account plus more recent material from Guericke.
 * 3. Otto von Guericke's Experimenta Nova (ut vocantur) Magdeburgica de Vacuo Spatio of 1672, published upon Guericke's initiative.
 * Book II: The Nature of Space and the Possibility of the Void
 * Book III: The Experimental Work on the Production of Vacua, The Pressure of Air and the Earth's Atmosphere
 * Book IV: The Investigation into Cosmic Potencies.

Nature of Space and the Possibility of the Void
Book II of the Experimenta Nova is an extended philosophical essay in which von Guericke puts forward a view of the nature of space similar to that later espoused by Newton. He is explicitly critical of the plenist views of Aristotle and of their adoption by his younger contemporary Descartes. A particular and repeated target of his criticism is the manner in which the "nature abhors a vacuum" principle had migrated from simply a matter of experiment to a high principle of physics which could be invoked to explain phenomena such as suction but which itself was above question. In setting out his own view, von Guericke, while acknowledging the influence of previous philosophers such as Lessius (but not Gassendi), makes it clear that he considers his thinking on this topic to be original and new. There is no evidence that von Guericke was aware of the Nouvelles Experiences touchant le vide of Blaise Pascal published in 1647. In the Experimenta Nova, Book III, Ch. 34, he relates how he first became aware of Torricelli's mercury tube experiment from Valerianus Magnus at Regensburg in 1654. Pascal's work built upon reports of the mercury tube experiment which had reached Paris via Marin Mersenne in 1644. An indication of the unresolved status of the "nature abhors a vacuum" principle at that time may be taken from Pascal's opinion, expressed in the conclusion of the Nouvelles Experiences, when he writes: "I hold for true the maxims set out below: (a) that all bodies possess a repugnance to being separated one from another and from admitting a vacuum in the interval between them – that is to say that nature abhors a void." Pascal goes on to claim that this abhorrence of a void is, however, a limited force and thus that the creation of a vacuum is possible.

There were three broad currents of opinion from which von Guericke dissented. Firstly, there was the Aristotelian view that there simply was no void and that everything that exists objectively is in the category of substance. The general plenist position lost credibility in the 17th century, owing primarily to the success of Newtonian mechanics. It was revived again in the 19th century as a theory of an all-pervading aether and again lost plausibility with the success of Special Relativity. Secondly, there was the Augustinian position of an intimate relation between space, time, and matter; all three, according to St. Augustine in the Confessions (Ch. XI) and the City of God (Book XI, Ch. VI), came into being as a unity and ways of speaking that purport to separate them – such as "outside the universe" or "before the beginning of the universe" are, in fact, meaningless. Augustine's way of thinking is also attractive to many and seems to have a strong resonance with General Relativity. The third view, which von Guericke discusses at length, but does not attribute to any individual, is that space is a creation of the human imagination. Thus, it is not truly objective in the sense in which matter is objective. The later theories of Leibniz and Kant seem inspired by this general outlook, but the denial of the objectivity of space has not been scientifically fruitful.

Von Guericke sidestepped the vexing question of the meaning of "nothing" by asserting that all objective reality fell into one of two categories – the created and the uncreated. Space and time were objectively real but were uncreated, whereas matter was created. In this way he created a new fundamental category alongside Aristotle's category of substance, that of the uncreated. His understanding of space is theological and similar to that expressed by Newton in the General Scholium to the Principia. For instance, von Guericke writes (Book II, Chapter VII): "For God cannot be contained in any location, nor in any vacuum, nor in any space, for He Himself is, of His nature, location and vacuum."

Air pressure and the vacuum
In 1650 von Guericke invented the vacuum pump. His model consisting of a piston and an air gun cylinder with two-way flaps designed to pull air out of whatever vessel it was connected to, and used it to investigate the properties of the vacuum in many experiments. Guericke demonstrated the force of air pressure with dramatic experiments.

In 1657, he machined two 20-inch diameter hemispheres and pumped all the air out of them, locking them together with a vacuum seal. The air pressure outside held the halves together so tightly that sixteen horses, eight harnessed to each side of the globe, could not pull the halves apart. It would have required more than 4,000 pounds of force to separate them. It is estimated that by pumping the air out of these spheres, he was able to reduce the internal pressure to roughly 1/25 of an atmosphere.

With his experiments Guericke disproved the hypothesis of "horror vacui", that nature abhors a vacuum. Aristotle (e.g. in Physics IV 6–9) had argued against the existence of the void and his views commanded near-universal endorsement by philosophers and scientists up to the 17th century. Guericke showed that substances were not pulled by a vacuum, but were pushed by the pressure of the surrounding fluids.

All of von Guericke's work on the vacuum and air pressure is described in Book III of the Experimenta Nova (1672). As regards the more detailed chronology of his work we have, in addition to the Experimenta Nova's description of his demonstrations at Regensburg in 1654, the two accounts published by Fr. Schott in 1657 and 1663.

In Chapter 27 he alludes to what transpired at Regensburg in 1654. The first experiment he explicitly records as having been demonstrated was the crushing of a non-spherical vessel as the air was withdrawn from it. He did not use a vacuum pump directly on the vessel, but allowed the air in it to expand into a previously evacuated receiver.

The second was an experiment in which a number of men proved able to pull an airtight piston only about halfway up a cylindrical copper vessel. Von Guericke then attached his evacuated receiver to the space below the piston and succeeded in drawing the piston back down again against the force of the men pulling it up. In a letter to Friar Schott of June 1656, reproduced in Mechanica Hydraulico-pneumatica (pp. 454–55), von Guericke gives a short account of his experiences at Regensburg. Based on this, Schimank [1936] gives a list of ten experiments that he considers likely to have been carried out at Regensburg. In addition to the above two, these included the extraction of air using a vacuum pump, the extinction of a flame in a sealed vessel, the raising of water by suction, a demonstration that air has weight, and a demonstration of how fog and mist can be produced in a sealed vessel. The Mechanica Hydraulico-pneumatica also provides the earliest drawing of von Guericke's vacuum pump. This corresponds to the description in the opening chapters of Book III of the Experimenta Nova of the first version of his pump.

Stimulated by the interest taken in his work, von Guericke was scientifically very active in the decade after 1654. In June 1656 we find him writing to Fr. Schott (Mechanica Hydraulico-pneumatica, p. 444) "Since the time when I produced the exhibition for the said eminent Elector, I have a better and clearer grasp of all these matters and many other topics as well." The celebrated hemispheres experiment was, as noted in the biographical section above, carried out between July 1656 and August 1657. In Chapter IV of Book III he describes a new and much-improved design of vacuum pump and attributes its invention to the need for a more easily transportable machine with which he could demonstrate his experiments to Frederick William, who had expressed the desire to see them. The new pump is also described on p. 67 of the Technica Curiosa. The demonstration in the Elector's Library at Cölln an der Spree took place in November 1663 and was recorded by a tutor to the Elector's sons. (Schneider p. 113.) A number of experiments, such as the rather cruel testing of the effect of a vacuum on birds and fish (Experimenta Nova, Book III, Chapter XVI), are not described in the Technica Curiosa. Although the Experimenta Nova does contain correspondence from 1665, there is no reason to doubt von Guericke's assertion that the work was essentially finished by March 1663.

Throughout Books II and III he returns again and again to the theme of there being no abhorrence of a vacuum and that all the phenomena explained by this supposed principle are in fact attributable to the pressure of the atmosphere in conjunction with various incorporeal potencies which he held to be acting. Thus the Earth's "conservative potency" (virtus conservativa) provided the explanation for the fact that the Earth retains its atmosphere though travelling through space. In countering the objection of a Dr. Deusing that the weight of the atmosphere would simply crush the bodies of all living things, he shows explicit awareness of the key property of a fluid – that it exerts pressure equally across all planes. In Chapter XXX of Book III he writes: "Dr. Deusing ought to have borne in mind that the air does not just press on our heads but flows all around us. Just as it presses from above on the head, it likewise presses on the soles of the feet from below and simultaneously on all parts of the body from all directions."

Relevant research
In the Experimenta Nova, Book III, Chapter 20, von Guericke reports on a barometer he had constructed and its application to weather forecasting. The earliest reference to his barometer is in a letter to Fr. Schott of November 1661 (Technica Curiosa, p. 37) where he writes: "I have observed the variation in the weight of the air by using a little man (i.e. a statue in the form of one) who hangs from a wall in my hypocaust where it floats on air in a glass tube and uses a finger to show the weight or lightness of the air. At the same time it indicates whether or not it is raining in nearby localities or whether there is unusually stormy weather at sea." In a subsequent letter of December 30, 1661 (Technica Curiosa p. 52) he gives a somewhat amplified account. His barometer thus prepared the way for meteorology. His later works focused on electricity. He invented the "Elektrisiermaschine", a version of which is illustrated in the engraving by Hubert-François Gravelot, c. 1750. This device, which is usually identified as the first electrostatic generator, was developed as part of von Guericke's interest in the worldly powers (mundane virtues) that operated in the universe. Von Guericke also showed that electrical (magnetic) attraction does not require a medium to operate in by an experiment using electrical transmission through linen thread.

Electrostatic investigations
Von Guericke thought of the capacity of body to exert an influence beyond its immediate boundaries in terms of "corporeal and incorporeal potencies". Examples of "corporeal potencies" were the giving off of fumes, smells, gases etc. by bodies. An example of an "incorporeal potencies" was the Earth's "conservative potency" whereby it retained its atmosphere and caused the return of objects thrown upwards to the Earth's surface. The Earth also possessed an "expulsive potency" which was deemed to explain why objects that fall bounce back up again. The notion of an "incorporeal potency" is similar to that of "action at a distance", except the former notion remained purely qualitative and there is no inkling of the fundamental "action and reaction" principle.

Von Guericke describes his work on electrostatics in Chapter 15 of Book IV of the Experimenta Nova. In a letter of November 1661 to Fr. Schott, reproduced in the Technica Curiosa, he notes that the then projected Book IV would be concerned with "cosmic potencies" (virtutes mundanae). Accepting the claim of the preface to the Experimenta Nova that the entire work had been essentially completed before March 1663, von Guericke can be fairly credited with inventing a primitive form of frictional electrical machine before 1663. His electrostatic generator was created using a sulphur globe attached to an iron rod. By rubbing the sphere with a dry hand, von Guericke was able to impart a charge imbalance on the surface, which would allow him to attract and repel other objects.

In Chapter 6 of Book IV von Guericke writes: "It seems reasonable to suppose that if the Earth has a fitting and appropriate attractive potency it will also have a potency of repelling things that might be dangerous or disagreeable to it. This is to be seen in the case of the sulphur sphere described below in Chapter 15. When that sphere is stroked or rubbed not only does it attract all light objects, but it sometimes arbitrarily also repels them before attracting them again. Sometimes indeed it doesn't even attract them again." Von Guericke was aware of both Gilbert's book On the Magnet and Magnetic bodies and on the great magnet the Earth (De Magnete) published in 1600 and of the Jesuit Niccolo Cabeo's Philosophia Magnetica (1629). He does not explicitly acknowledge any anticipation of his demonstration of electrostatic repulsion by the latter but, as he quotes a passage from the same page, could not have been unaware that, in a discussion of the nature of electrical attraction, Cabeo had written (Philosophia Magnetica, p. 192): "When we see that small bodies (corpuscula) are lifted (sublevari et attolli) above the amber and also fall back to the motionless amber, it cannot be said that such erratic behaviour (talem matum – but if "matum" is taken as a misprint for "motum", then the translation is simply "such motion") is an attraction by the gravity of the attracting body." In Book IV, Chapter 8 of the Experimenta Nova von Guericke is at pains to point out the difference between his own "incorporeal potency" views and Cabeo's more Aristotelian conclusions. He writes: "Writers who have written on magnetism, always confuse it with electrical attraction, although there is a great difference. In particular, Gilbert in his book De Magnete claims that electrical attraction is caused by the effluence of a humour, that the humid seeks the humid and this is the cause of the attraction. Moreover in Philosophia Magnetica, Book 2, Chapter 21, Cabeo criticises Gilbert but does admit that this attraction is created by the agency of an effluent. Humidity does not play any role but the attraction is brought about purely by the agency of an effluent, by which the air is disturbed. After the initial impulse, the air returns to the amber again taking with it little particles. He (Cabeo) concludes by saying: 'I say therefore that from amber or any other electrically attracting body, a very rarefied effluent is emitted which dispels and attenuates the air, extremely agitating it. Then the agitated and attenuated air returns to the amber body sweeping along with it whatever dust or small bodies are in its way'. We however, who in the previous chapter, take the attraction of the sulphur ball as electrical in nature and operating through a conservative potency, cannot admit that the air plays a role in producing the attraction. Experiment visibly shows that this sulphur globe (once it has been rubbed) also exercises its potency through a linen cord up to a range of a cubit and more and can attract at that distance." Unknown to them at the time, this "mysterious" attraction and repulsion they had been witnessing was actually electrical conduction.

The key Chapter 15 is titled "On an experiment, in which these potencies, listed above, can be evoked by the rubbing of a sulphur ball." In Section 3 of this chapter, he describes how light bodies are repelled from a sulphur sphere which has been rubbed with a dry hand, and are not again attracted until they have touched another body. Oldenburg's review of the Experimenta Nova (November 1672) in the Proceedings of the Royal Society sceptically observes: "How far this globe may be confided in, the Tryals and Consideration of some ingenious person here may perhaps inform us hereafter." In fact, Robert Boyle repeated von Guericke's experiments for the Royal Society in November 1672 and February 1673.

title: Otto von Guericke


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Material dispersion coefficient

In an optical fiber, the material dispersion coefficient, M(λ), characterizes the amount of pulse broadening by material dispersion per unit length of fiber and per unit of spectral width. It is usually expressed in picoseconds per (nanometre·kilometre).

For many optical fiber materials, M(λ) approaches zero at a specific wavelength λ0 between 1.3 and 1.5 μm. At wavelengths shorter than λ0, M(λ) is negative and increases with wavelength; at wavelengths longer than λ0, M(λ) is positive and decreases with wavelength.

Pulse broadening caused by material dispersion in a unit length of optical fiber is given by the product of M(λ) and spectral width (Δλ).

title: Material dispersion coefficient


text:
Light pen

A light pen is a computer input device in the form of a light-sensitive wand used in conjunction with a computer's cathode-ray tube (CRT) display.

It allows the user to point to displayed objects or draw on the screen in a similar way to a touchscreen but with greater positional accuracy. A light pen can work with any CRT-based display, but its ability to be used with LCDs was unclear (though Toshiba and Hitachi displayed a similar idea at the "Display 2006" show in Japan ).

A light pen detects changes in brightness of nearby screen pixels when scanned by cathode-ray tube electron beam and communicates the timing of this event to the computer. Since a CRT scans the entire screen one pixel at a time, the computer can keep track of the expected time of scanning various locations on screen by the beam and infer the pen's position from the latest time stamps.

History
The first light pen, at this time still called "light gun", was created around 1951–1955 as part of the Whirlwind I project at MIT, where it was used to select discrete symbols on the screen,   and later at the SAGE project, where it was used for tactical real-time-control of a radar-networked airspace.

One of the first more widely deployed uses was in the Situation Display consoles of the AN/FSQ-7 for military airspace surveillance. This is not very surprising, given its relationship with the Whirlwind projects. See Semi-Automatic Ground Environment for more details.

During the 1960s, light pens were common on graphics terminals such as the IBM 2250 and were also available for the IBM 3270 text-only terminal.

The first nonlinear editor, the CMX 600 was controlled by a light pen, where operator clicked symbols superimposed on edited footage.

Light pen usage was expanded in the early 1980s to music workstations such as the Fairlight CMI and personal computers such as the BBC Micro and Holborn 9100. IBM PC-compatible MDA (only early versions), CGA, HGC (including HGC+ and InColor ) and some EGA graphics cards also featured a connector compatible with a light pen, as did early Tandy 1000 computers, the Thomson MO5 computer family, the Amiga, Atari 8-bit, Commodore 8-bit, some MSX computers and Amstrad PCW home computers. For the MSX computers, Sanyo produced a light pen interface cartridge.

Because the user was required to hold their arm in front of the screen for long periods of time (potentially causing "gorilla arm") or to use a desk that tilts the monitor, the light pen fell out of use as a general-purpose input device. Light pen was also perceived as working well only on displays with low persistence, which tend to flicker.

title: Light pen