Zheng He: see Cheng Ho.

Huang He, Hwang Ho, or Yellow River, great river of N China, c.3,000 mi (4,830 km) long, rising in the twin lakes Gyaring and Ngoring in the Kunlun Mts., NW Qinghai prov., and flowing generally east into the "great northern bend" (around the Ordos Desert), then east again to the Bohai, an arm of the Yellow Sea.

Course

The turbulent upper Huang He meanders east through a series of gorges to the fertile Lanzhou valley. Hydroelectric dams in the Liujia gorge and at Lanzhou, the largest city on the river, generate electricity and impound irrigation water. Past Lanzhou, the Huang He becomes a wide, slow-moving stream as it begins its bend around the Ordos and separates the northern uplands from the desert and loess lands of the south and west. It is navigable in places for small vessels. The west end of the "great northern bend" passes through the heavily populated Ningxia agricultural region, a heavily irrigated oasis c.60 mi (100 km) long, where cereals and fruits are raised. At the northwest corner of the "great northern bend," the Huang He divides into numerous branches, watering a fertile area where ancient irrigation canals have been repaired and are now in use. At the northeast corner lies the most fertile land outside the Great Wall; it was farmed without irrigation until 1929.

Turning south, the Huang He passes through the Great Wall and enters the fertile loess region (where rich coal deposits are also found on both sides of the river). Cutting deep into the loess, the river receives most of the yellow silt from which its name is derived. After receiving the Wei and Fen rivers, its chief tributaries, the Huang He turns east and flows through Sanmen gorge, site of the Sanmenxia dam, which is used for power production, flood control, and navigation. Below the Sanmenxia dam is the multipurpose Xiaolangdi dam, located in the river's last valley before the North China Plain, a great delta created from silt dropped at the Huang He's mouth over the millennia. The North China Plain extends over much of Henan, Hebei, and Shandong provs. and merges with the Chang (Yangtze) delta in N Jiangsu and N Anhui provs. The Huang He meanders over the fertile, densely populated plain to reach the Bohai. The plain is one of China's most important agricultural regions, producing corn, sorghum, winter wheat, vegetables, and cotton.

Ancient Floods and Recent Water Scarcity

During the winter dry season the Huang He is slow-moving and silt-laden, and occupies only part of its huge bed; with the summer rains, it can become a raging torrent. Since the 2d cent. B.C., the lower Huang He has inundated the surrounding region some 1,500 times and has made nine major changes in its course. In an attempt to halt the Japanese invasion of China in 1938, the Chinese diverted the Huang He south, flooding more than 20,000 sq mi (51,800 sq km) and killing some 900,000 people; it was returned to its present course in 1947.

The Chinese have long sought to control the Huang He by building dikes and overflow channels. Silt deposition, the principal cause of flooding, has elevated the riverbed; in places the river flows 60 to 70 ft (18-21 m) above the surrounding plains. During the summer high-water period, water pressure against the dikes can break through the retaining walls to cause devastating floods, which have led the Huang He to be called "China's Sorrow." In 1955 the Chinese initiated a 50-year construction plan for control of the river. Dikes have been repaired and reinforced, and a series of silt-retaining dams are being constructed to control the upper river, produce electricity, and provide water for irrigation. The People's Victory Canal, a 40-mi-long (64-km) diversion and irrigation channel, connects the Huang He with the Wei River.

In recent years, however, extensive use of the river's waters has severely reduced the flow of the Huang He in its lower reaches. In 2000 the Chinese government embarked on program to replenish the oversubscribed waters of the Huang He with those of the Chang (Yangtze); three sets of canals would divert water from the upper, middle, and lower Chang. Although the work on the upper (western) diversion routes could take as much as 50 years, much of the work on the other routes was expected to be completed in a decade.

He, symbol for the element helium.

Bad Homburg vor der Höhe, Bad Homburg, or Homburg, city (1994 pop. 51,455), Hesse, central Germany, at the foot of the Taunus Mts. It is a famous spa and resort. Manufactures include foodstuffs, machinery, textiles, and leather goods. Chartered in the early 14th cent., Bad Homburg was from 1622 to 1866 the capital of the landgraviate of Hesse-Homburg.

or Cheng Ho orig. Ma Sanbao

(born circa 1371, Kunyang, Yunnan province, China—died April 1433, Calicut, India) Eunuch admiral and diplomat who helped extend Chinese maritime and commercial influence throughout the region bordering on the Indian Ocean.The Yongle emperor named Zheng commander in chief of missions to the “Western Oceans.” He first set sail in 1405 and on this mission visited Champa (southern Vietnam), Siam (Thailand), Malacca, and Java, traveled through the Indian Ocean as far as Sri Lanka, and returned to China in 1407. Subsequent voyages took him to Arabia, the eastern coast of Africa, Southeast Asia, and India. Chinese emigration to, and influence in, Southeast Asia increased in the wake of these missions, resulting in tributary trade to China that lasted into the 19th century.

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or Huang Ho English Yellow River

River, northern, central, and eastern China. The second longest river in China and one of the world's longest, it flows 3,395 mi (5,464 km) from the Plateau of Tibet generally east to the Yellow Sea (Huang Hai). In its lower reaches it has often overflowed its banks, flooding vast areas of rich farmland. Its outlet has shifted over the years to enter the Yellow Sea at points as far apart as 500 mi (800 km). Irrigation and flood-control works have been maintained for centuries, and dams, begun in the mid-1950s, exploit the river's hydroelectric potential.

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Method of dating that depends on the production of helium during the decay of radioactive isotopes of uranium and thorium. Because of this decay, the helium content of any mineral or rock capable of retaining helium will increase during the lifetime of that mineral or rock, and the ratio of helium to its radioactive progenitors then becomes a measure of geologic time. Fossils may also be dated by helium dating. The relatively large amount of helium produced in rocks may make it possible to extend helium dating to rocks and minerals as young as a few tens of thousands of years old.

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Chemical element, chemical symbol He, atomic number 2. A noble gas, it is colourless, odourless, tasteless, completely unreactive, and nontoxic. First found by spectroscopy of the Sun's atmosphere in 1868, it is the second most abundant and second-lightest element in the universe (after hydrogen). Helium makes up a tiny proportion of the atmosphere but as much as 7percnt of natural gas. It is the product of radioactive decay (see radioactivity) and is used in helium dating. It is used as an inert gas in welding, rocket propulsion, balloon flight, hyperbaric chambers, deep-sea diving (see nitrogen narcosis), gas chromatography, luminous signs, and cryogenics. Liquid helium, which exists only below −452 °F (−268.9 °C, about 4° C above absolute zero), is a “quantum fluid” (see fluid mechanics; quantum mechanics), with unique properties, including superfluidity, superconductivity, and near-zero viscosity.

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