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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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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(1968) Brief period of liberalization in Czechoslovakia under
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