spring peeper: see tree frog.

spring beauty: see purslane.

spring, in geology, natural flow of water from the ground or from rocks, representing an outlet for the water that has accumulated in permeable rock strata underground. Some of the water that falls as rain soaks into the soil and is drawn downward by gravity to a depth where all openings and pore spaces in the rock or soil have become completely saturated with water. This region is called the zone of saturation, and the water it holds, groundwater. The upper surface of the zone of saturation is called the water table. Above the water table lies the zone of aeration, where the pore spaces in the soil are quite dry and are filled with air. When the upper surface of the groundwater (water table) intersects a sloping land surface, a spring appears. The occurrence of springs is closely related to the geology of an area. If an impervious layer of rock, such as a clay deposit, underlies a layer of saturated soil or rock, then a line of springs will tend to appear on a slope where the clay layer outcrops. Igneous rocks are also impervious to water, yet they are often extensively fractured, and springs commonly appear where these fractures come to the surface. Fractures in limestone are often enlarged by the dissolving action of groundwater, forming small underground channels and caves. Where these channels outcrop, springs are likely to be found. Springs are common along major faults because groundwater reaches the surface along the fault plane. Lines of springs help locate the position of faults such as the San Andreas of California. Springs can be a valuable water resource, and improvement in flow can often be accomplished simply by driving a pipe into the ground at the point where water seeps from the ground. Sometimes it is advisable to divert the spring water into a cistern or other storage reservoir from which the water can be pumped at will. When the water, because of the geological structure of the strata, issues under pressure, the spring is called artesian (see artesian well). Another type of spring is the geyser. Hot springs occur when the water issues from great depths or is heated by near-surface hot volcanic rock, as in Yellowstone National Park, Iceland, and New Zealand. Mineral springs are those with a high mineral content, usually silica or lime, dissolved from the rocks through which the water has passed (see mineral water). Many ancient city-states, such as Troy, had their sites determined by springs. Pioneer farmhouses often were located in the same way.

spring, in mechanics, any of several elastic devices used variously to store and to furnish energy, to absorb shock, to sustain the pressure between contacting surfaces, and to resist tensional or compressional stress. Springs are made of an elastic material, e.g., specially formulated steel alloys or certain types of rubber or plastic. A torsion spring that stores energy, e.g., for operating a watch, is a metal strip wound spirally around a fixed center. For reducing concussion in some heavy trucks and railroad cars, helical, or coil, springs are used. Coil springs are commonly used for the same purpose in automobiles, as are leaf springs that consist of flat bars clamped together. These have been replaced in some vehicles by torsion bars that absorb stresses by twisting. The helical-coil compression spring provides the force to keep the operating surfaces together in the friction clutch (see transmission). The extension spring is employed for the spring balance; the distance through which it is extended depends on the weight suspended from it. The disk spring, which consists of a laminated series of convex disks, is widely employed for heavy loads.

hot spring, natural discharge of groundwater having an elevated temperature. Most hot springs result from the emergence of groundwater that has passed through or near recently formed, hot, igneous rocks. Iceland, Yellowstone Park in the United States, and North Island of New Zealand are noted for their hot springs. In recent years the depletion of fossil fuels has resulted in a renewed interest in utilizing the energy contained in hot springs. This type of geothermal energy is already being utilized in California, Italy, and Iceland. See energy, sources of.

Spring Valley. 1 Uninc. community (1990 pop. 55,331), within the confines of San Diego, San Diego co., SW Calif., on Sweetwater Lake. It is a rapidly growing residential community, with some light industrial production (transportation equipment and paper and metal products). The Bancroft Ranch House Museum (1856) is a national historic landmark. 2 Residential village (1990 pop. 21,802), Rockland co., SE N.Y., near the N.J. line; inc. 1902. It is a fast-growing suburb with office complexes and shopping malls.

Silver Spring, uninc. city (1990 pop. 76,046), Montgomery co., W central Md., a residential suburb of Washington, D.C. It is a major suburban office center and has a large naval ordnance laboratory, several research laboratories (for the development of defense materials and of electronic and prosthetic equipment), and a plant that makes precision instruments.

Siding Spring Observatory, astronomical observatory located on Siding Spring Mountain, near Coonabarabran, at an altitude of nearly 4,000 ft (1,220 m) in the Warrumbungle Mts. of New South Wales, Australia. It began as a field station for Mt. Stromlo Observatory and is operated by the Australian National Univ. The principal instrument is a 153-in. (389-cm) reflecting telescope, which was jointly financed by the Australian and British governments. Other equipment includes 40-in. (102-cm) and 26-in. (66-cm) reflectors, a 48-in. (122-cm) Schmidt camera telescope similar to that at Palomar Observatory, and a 24-in. (61-cm) rotating telescope used for measuring the polarization of starlight.

Prague Spring: see Prague and Czechoslovakia.

Pipe Spring National Monument: see National Parks and Monuments (table).

Houghton-le-Spring, town (1991 pop. 35,337), Sunderland metropolitan district, NE England. Once a coal mining center, it is now a market town.

Big Spring, city (1990 pop. 23,093), seat of Howard co., W central Tex.; inc. 1907. The spring for which it was named once fed a branch of the Colorado River but has become dry. The city is the trade center for a farm and cattle region. A variety of oil- and gas-related industries have been developed since the discovery of oil in 1928. Of interest are a historical museum and the Comanche Trail Park.

or thermal spring

Spring that issues water at temperatures substantially higher than the air temperature of the surrounding region. Most hot springs result from the interaction of groundwater with magma or with solid but still-hot igneous rocks. Some, however, are not related to volcanic activity. In such cases, deep circulation of water is thought to carry the water to the lower parts of the Earth's crust, where the temperature of the rocks is high.

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Species (Hyla crucifer) of tree frog found in ponds, marshes, and other damp areas in the U.S. During the breeding season it can be found in woodland ponds; at other times it is seldom seen. It has a high, whistling call and is one of the first frogs to vocalize in spring. It is tiny (only 0.75–1.3 in. or 2–3.5 cm, long) and grayish, tan, or olive-brown, with an X-shaped or irregular brown mark on its back.

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Weighing device that uses the relation between the applied load and the deformation of a spring. This relationship is usually linear; that is, if the load is doubled, the deformation is doubled. Spring balances are widely used commercially. Those with high load capacities are frequently suspended from crane hooks and are known as crane scales.

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Elastic machine component able to deflect under load in a prescribed manner and to recover its initial shape when unloaded. The combination of force and displacement in a deflected spring is energy, which may be stored when moving loads are being stopped or when the spring is wound up for use as a power source (e.g., in a watch). Though most springs are mechanical, hydraulic (liquid) and air springs exist.

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(1968) Brief period of liberalization in Czechoslovakia under Alexander Dubchacekek. In April 1968 he instituted agricultural and industrial reforms, a revised constitution to guarantee civil rights, autonomy for Slovakia, and democratization of the government and the Communist Party. By June, many Czechs were calling for more rapid progress toward real democracy. Although Dubchacekek believed he could control the situation, the Soviet Union and the Warsaw Pact countries, alarmed by the threat of a social-democratic Czechoslovakia, invaded the country in August, deposed Dubchacekek, and gradually restored control by reinstalling hard-line communists as leaders.

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