Wat Tyler's Rebellion See Peasants' Revolt
watch Portable timepiece designed to be worn on the wrist or carried in the pocket. The first watches appeared shortly after 1500, when the mainspring (see spring) was invented as a replacement for weights in driving CLOCKS. The progressive miniaturization of electronic components in recent decades has made possible the development of all-electronic watches, in which the necessary transistors, resistors, capacitors, and other elements are all on one or several miniature integrated circuits, or chips. Such circuitry enables them to perform several timekeeping functions and also makes possible digital readouts of the time.
water Inorganic compound composed of hydrogen and oxygen (H 2 0), existing in liquid, gas (steam, water vapour), and solid (ice) states. At room temperature, water is a colourless, odourless, tasteless liquid. One of the most abundant compounds, water covers about 75% of Earth’s surface. Life depends on water for virtually every process, its ability to dissolve many other substances being perhaps its most essential quality. Life is believed to have originated in water (the world’s oceans or smaller bod¬ ies), and living organisms use aqueous solutions (including blood and digestive juices) as mediums for carrying out biological processes. Because water molecules are asymmetric and therefore electric dipoles, hydrogen bonding between molecules in liquid water and in ice is impor¬ tant in holding them together. Many of water’s complex and anomalous physical and chemical properties (high melting and boiling points, viscos¬ ity, surface tension, greater density in liquid than in solid form) arise from this extensive hydrogen bonding. Water undergoes dissociation to the ions H + (or H 3 0 + ) and OH - , particularly in the presence of salts and other solutes; it may act as an acid or as a base. Water occurs bound (as water of hydration) in many salts and minerals. It has myriad industrial uses, including as a suspending agent (papermaking, coal slurrying), solvent, diluting agent, coolant, and source of hydrogen; it is used in filtration, washing, steam generation, hydration of lime and cement, textile process¬ ing, sulfur mining, hydrolysis, and hydraulics, as well as in beverages and foods. See also hard water; heavy water.
water bloom Dense aquatic accumulation of microscopic organisms produced by an abundance of nutrients in surface water coupled with adequate sunlight for photosynthesis. The microorganisms or the toxic substances they release may discolour the water, exhaust its oxygen con¬ tent, poison aquatic animals and waterfowl, and irritate the skin and res¬ piratory tract of humans. Single species of algae, diatoms, or dinoflagellates, reproducing every few hours, may dominate a bloom’s population; the number of individuals per quart (litre) of water, normally about 1,000, can increase to 60 million. Blooms of the dinoflagellate genus Gymnodinium cause red tides. The Red Sea is named for the occa¬ sional blooms of the alga Trichodesmium erythraeum. See also water pol¬ lution.
water buffalo or Indian buffalo Any of three subspecies of oxlike bovid (species Bubalus bubalis). Two have been domesticated in Asia since
the earliest recorded history. The animal is named for its ability to work on waterlogged land and in humid climates. The largest breeds stand 5-6 ft (1.5-1.8 m), is up to 9 ft (2.8 m) long, and may weigh over 2,000 lb (900 kg). The dull black or dark gray body has little hair. The horns spread outward and upward, measuring up to 7 ft (2 m) across. One subspecies, the swamp buffalo, is the principal draft animal of southern China and South and Southeast Asia. Another, the river buffalo, is used for dairy and meat production and draft work in southern and South Asia and Egypt. The third subspecies is the wild water buffalo, of which only a few dozen herds remain. It is larger than domestic buffaloes and is sometimes referred to as a separate species {B. arnee).
water chestnut Any of several perennial water plants of the genus Trapa (family Trapaceae), native to Europe, Asia, and Africa, or their edible, nutlike fruit. The water caltrop (T. natans) has two sets of leaves— long, feathery, rootlike, submerged leaves and a loose rosette of floating leaves attached to leafstalks 2-4 in (5-10 cm) long. The small fruit usu¬ ally has four spiny angles. The Chinese water chestnut (. Eleocharis tubero- sus or E. dulcis) is a member of the sedge family.
water clock or clepsydra Vklep-so-droX Ancient device for measur¬ ing time by the gradual flow of water. One form, used by North Ameri¬ can Indians and some African peoples, consisted of a small boat or floating vessel that shipped water through a hole until it sank. In another form, water escaped through a hole in a vessel marked with graduated lines; specimens from Egypt date from the 14th century bc. The Romans invented a clepsydra consisting of a cylinder into which water dripped from a reservoir; a float provided readings against a scale on the cylinder wall. Galileo used a mercury clepsydra to time his experimental falling bodies. See also clock.
water flea Any of about 450 species (order Anomopoda) of micro¬ scopic, mostly freshwater crusta¬ ceans distributed worldwide. Species in the genus Daphnia are ubiquitous in Europe and North America. Water fleas have a discrete head that bears antennae. The carapace (shell) encloses all or most of the body, except on the predatory giant Lep- todora (up to 0.7 in. [18 mm] long), whose carapace is just a small brood sac. Most species swim by powerful strokes of the antennae, sometimes producing a hopping-and-sinking motion. All but a few predatory spe¬ cies use specialized thoracic limbs to filter organic matter from the water. See also copepod.
water frame In textile manufacture, a spinning machine powered by water that produced a cotton yarn suitable for warp (lengthwise threads). Patented in 1769 by R. Arkwright, it represented an improvement on James Hargreaves’s spinning jenny, which produced weaker thread suitable only for weft (filling yam).
water hyacinth Any of about five species of aquatic plants that make up the genus Eichhornia of the pick¬ erel weed family (Pontederiaceae).
They are native mainly to the New World tropics. Some species float in shallow water; others are rooted in muddy streambanks and lakeshores.
All have slender rootstocks, feathery roots, rosettes of stalked leaves, and flowers arranged in spikes or clus¬ ters. The common water hyacinth (E. crassipes ) is the most widespread.
The leafstalk is spongy and inflated, and the upper lobes of its purple flowers have blue and yellow mark¬ ings. It reproduces quickly, often clogging slow-flowing streams. It is used as an ornamental in outdoor pools and aquariums.
water lily Any of the freshwater plants in eight genera that make up the family Nymphaeaceae, native to temperate and tropical regions. All are perennial except those in the genus Euryale. Most have rounded, floating, waxy-coated leaves growing atop long stalks that contain many
Water flea of the genus Daphnia (mag¬ nified about 30x)
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2034 I water moccasin ► watercress
air spaces. Thick, fleshy, creeping underwater stems are buried in the mud. In some species the leaves are also submerged. Showy, solitary, cuplike flowers with numerous spi¬ rally arranged petals are borne at or above the water surface on the long stalks. The genus Nymphaea includes the water lilies proper (or water nymphs). The common North American white water lily, pond lily, or toad lily is N. odorata. The LOTUS of ancient Egyptian art was usually the blue lotus ( N. caerulea). The largest water lilies are two species that make up the tropical South American genus Victoria ; the Santa Cruz water lily ( V. cruziana ) has leaves 2-6 ft (60-180 cm) in diam¬ eter. Water lilies provide food for fish and wildlife but sometimes cause drainage problems because of their rapid growth. Many varieties have been developed for ornamental use in gar¬ den pools and conservatories.