CHAMBER encyclopedia topics

spark chamber, in physics, device for recording the passage of elementary particles produced by reactions in a particle accelerator. Particles pass through a stack of metal plates or wire grids that are maintained with high voltage between alternate layers. A high-pressure gas fills the gaps between the plates and is ionized along the path of the traversing charged particle. As a result, sparks jump between adjacent, oppositely charged plates and the trail of sparks left by the particle is seen as a series of dashes. The spark chamber has replaced the bubble chamber in certain applications. Although the particle paths are recorded more accurately in the bubble chamber, the bubble chamber indiscriminately records all events that occur in a comparatively long interval. The spark chamber operates much more rapidly and can be made highly selective by using auxiliary detectors to screen out unwanted events. Because of its selectivity, the spark chamber is most useful in searching for very rare events. Spark chambers can be highly automated, with data collected and stored electronically instead of photographically, as is necessary with the bubble chamber. The analysis of the data can then be accomplished by a high-speed computer, which may operate simultaneously with the experiment and thereby provide immediate evaluation of the quality of the data and allow optimum operating conditions to be maintained at all times.

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lead chamber process

lead chamber process: see sulfuric acid.

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ionization chamber

ionization chamber, device for the detection and measurement of ionizing radiation. It consists basically of a sealed chamber containing a gas and two electrodes between which a voltage is maintained by an external circuit. When ionizing radiation, e.g., a photon, enters the chamber (through a foil-covered window), it ionizes one or more gas molecules. The ions are attracted to the oppositely charged electrodes; their presence causes a momentary drop in the voltage, which is recorded by the external circuit. The observed voltage drop helps identify the radiation because it depends on the degree of ionization, which in turn depends on the charge, mass, and speed of the photon. See radioactivity.

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cloud chamber

cloud chamber, device used to detect elementary particles and other ionizing radiation. A cloud chamber consists essentially of a closed container filled with a supersaturated vapor, e.g., water in air. When ionizing radiation passes through the vapor, it leaves a trail of charged particles (ions) that serve as condensation centers for the vapor, which condenses around them. The path of the radiation is thus indicated by tracks of tiny liquid droplets in the supersaturated vapor. The cloud chamber was invented c.1900 by C. T. R. Wilson. In the type devised by him, which is often called the Wilson cloud chamber, air or another gas is saturated with water vapor and enclosed in a cylinder fitted with a transparent window at the top and a piston or other pressure-regulating device at the bottom. When the pressure in the chamber is suddenly reduced, e.g., by lowering the piston, the gas-vapor mixture is cooled, producing supersaturation. Cloud chambers of this design are sometimes called the pulsed type, since they do not maintain a continuous state of supersaturation of the vapor. A more recent design is the diffusion cloud chamber. In this device a large temperature difference is maintained between the top and bottom of the chamber, usually by cooling the bottom of the chamber with dry ice. The gas in the chamber, usually air, is saturated with a vapor, usually alcohol; the air-vapor mixture cools as it diffuses toward the cool bottom, becoming supersaturated. If the gas is kept saturated with a fresh supply of vapor, e.g., by an alcohol-soaked pad inside the top of the chamber, the operation of the chamber can be essentially continuous. One disadvantage of the cloud chamber is the relatively low density of the gas, which limits the number of interactions between ionizing radiation and molecules of the gas. For this reason physicists have developed other particle detectors, notably the bubble chamber and the spark chamber.

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chamber of commerce

chamber of commerce, local association of business people organized to promote the welfare of their community, especially its commercial interests. Each chamber of commerce usually has an elected board of directors, and its work is done through committees. Among the activities frequently carried on by these committees are industrial surveys and efforts to attract new industries to the city, the provision of information and advice to government on topics ranging from labor disputes to taxes, and the promotion of tourism in cities.

The chambre de commerce of Marseilles (1599) was the first organization to use the name; the idea spread through France in the 17th and 18th cent. The first to be formed in Great Britain was on the island of Jersey (1768). In America the first was the Chamber of Commerce of the State of New York, organized in 1768. By 1870 there were 40 throughout the United States.

The local chambers are federated in the United States Chamber of Commerce (founded 1912), which maintains at its Washington, D.C., headquarters a technical staff and lobbies in the interests of its member organizations. Its membership includes 3 million companies, 3,000 state and local chapters, and 830 business associations; American chambers are located in 82 foreign countries, and those of other countries have offices in the United States. The International Chamber of Commerce (founded 1920) promotes open international trade and investment. Its headquarters are in Paris.

See also trade association.

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chamber music

chamber music, ensemble music for small groups of instruments, with only one player to each part. Its essence is individual treatment of parts and the exclusion of virtuosic elements. Originally played by amateurs in courts and aristocratic circles, it began to be performed by professionals only in the 19th cent. with the rise of the concert hall. In the broadest sense it existed as early as the Middle Ages. The ricercare and the concerted canzone of the 16th cent. are properly chamber music, although unlike later forms they were not for specific instruments but were usually performed by voices and whatever instruments were at hand. During the baroque period the chief type was the trio sonata. About 1750 the string quartet with its related types—trio, quintet, sextet, septet, and octet—arose. As developed by Haydn and Mozart the quartet became the principal chamber-music form. It was used by Beethoven and Schubert, whose quartets are the last of the classical period, and by the chief composers of the romantic period—Mendelssohn, Schumann, Brahms, Dvořák, Franck, d'Indy, and Reger. In the early 20th cent. the coloristic possibilities of the quartet were exploited by Debussy and Ravel. More recently the different forms of chamber music have been used extensively for experiments in atonality, percussive rhythms, and serial techniques by such composers as Schoenberg, Bartók, Webern, Berg, Stravinsky, Sessions, and Piston.

See D. F. Tovey, Essays in Musical Analysis: Chamber Music (1944, 4th impression 1956); W. W. Cobbett, ed., Cyclopedic Survey of Chamber Music (3 vol., 2d ed. 1963, repr. 1987); H. E. Ulrich, Chamber Music (2d ed. 1966); M. Berger, Guide to Chamber Music (1985).

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bubble chamber

bubble chamber, device for detecting charged particles and other radiation by means of tracks of bubbles left in a chamber filled with liquid hydrogen or other liquefied gas. It was invented in 1952 by Donald Glaser. The bubble chamber consists essentially of a sealed chamber to be filled with a liquefied gas and constructed so that the pressure inside can be reduced quickly. The liquid is originally at a temperature just below its boiling point. When the pressure is reduced, the boiling point becomes lowered so that it is less than the temperature of the liquid, leaving the liquid superheated. When a charged particle passes through this superheated liquid, it leaves a trail of tiny gas bubbles that can be illuminated and photographed. The track of a charged particle can be used to identify the particle and to analyze complex events in which it may be involved. If a magnetic field is present, the tracks of the particles will be curved, positively charged particles curving in one direction and negatively charged particles curving in the opposite direction. The degree of curvature depends on the mass, speed, and charge of the particle. Neutral particles can be detected indirectly by applying various conservation laws to the events recorded in the bubble chamber or by observing their decay into pairs of oppositely charged particles. The bubble chamber is particularly useful for studying high-energy particles that would pass through a cloud chamber too quickly to leave a detailed enough track but which pass more slowly through the bubble chamber because of the greater density of the liquid. Liquid hydrogen and helium are commonly used in bubble chambers, with special equipment needed to maintain these gases in their liquid state (see low-temperature physics). For experiments requiring very dense liquids, a variety of organic compounds may be used. See elementary particles; particle accelerator; spark chamber.

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Wilson cloud chamber

Wilson cloud chamber: see cloud chamber.

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Star Chamber

Star Chamber, ancient meeting place of the king of England's councilors in the palace of Westminster in London, so called because of stars painted on the ceiling. The court of the Star Chamber developed from the judicial proceedings traditionally carried out by the king and his council, and was entirely separate from the common-law courts of the day. In the 15th cent., under the Lancastrian and Yorkist kings, the role of the council as an equity and prerogative court increased, and it extended its jurisdiction over criminal matters. Faster and less rigid than the common-law courts, its scope was extended by the Tudors. Under Chancellor Wolsey's leadership (1515-29), the Court of Star Chamber became a political weapon, bringing actions against opponents to the decrees and edicts of Henry VIII. Wolsey also encouraged petitioners to use the Court of the Star Chamber as a court of original jurisdiction, not as a last resort after the common-law courts had failed. Depositions were taken from witnesses, but no jury was employed in the proceedings. Although its sentences included a wide variety of corporal punishments, including whipping, pillorying, and branding, those convicted were never sentenced to death. The court remained active through the reigns of James I and Charles I. The traditional hostility between equity and common law was aggravated by the use made of the Star Chamber by the Stuarts as a vehicle for exercising the royal prerogative, particularly over church matters, in defiance of Parliament. It was abolished by the Long Parliament in 1641. In its later period the court was so reviled that Star Chamber became a byword for unfair judicial proceedings. The court's harshness, however, has been exaggerated.

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hyperbaric chamber

or decompression chamber or recompression chamber

Sealed chamber supplying a high-pressure atmosphere primarily for medical therapy. Breathing air or oxygen at typically 1.5–3 times normal pressure increases the oxygen level in tissues. This effect is used, for example, to treat carbon monoxide poisoning or to inhibit growth of anaerobic bacteria (as in gas gangrene). The compressive effect of the elevated pressure causes damaging gas bubbles in tissues (as in air embolism or decompression sickness) to shrink and gradually be absorbed.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

cloud chamber

Radiation detector developed by C.T.R. Wilson. Its detecting medium is a supersaturated vapour (see saturation) that condenses around ions produced by the passage of energetic charged particles, such as alpha particles, beta particles, or protons. In a Wilson cloud chamber, supersaturation is caused by the cooling induced by a sudden expansion of the saturated vapour by the motion of a piston or an elastic membrane. In a diffusion chamber, the saturated vapour is cooled to supersaturation as it diffuses into a region kept cold by a coolant such as solid carbon dioxide or liquid helium.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

chamber of commerce

or commercial association

Any of various voluntary organizations of business firms, public officials, professional people, and public-spirited citizens whose primary interest is in publicizing, promoting, and developing commercial and industrial opportunities in their local area, and usually also community schools, streets, housing, and public works. The International Chamber of Commerce (founded 1920) acts as the voice of the business community in the international field and runs a court of arbitration for settling commercial disputes. National chambers of commerce exist in most industrialized, free-enterprise countries. The first to use the name was founded in Paris in 1601; the first U.S. chamber of commerce was that of the state of New York, founded in 1768.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

chamber music

Music composed for small instrumental ensembles and performed without a conductor. Traditionally intended for performance in a room or reception hall, often solely for the performers' own pleasure, chamber music is now often heard in concert halls. It began with the 16th-century instrumental consort, and long continued to be associated with aristocratic households. The duo sonata (usually for violin and continuo) and trio sonata appeared in early 17th-century Italy. The string quartet arose in the 1750s and remains the best-known chamber genre and ensemble. The serenade, nocturne, and divertimento were Classical genres for varying instrumental forces, often intended to accompany meals and other activities. Standard ensembles include the string trio (violin, viola, cello), string quintet (two violins, two violas, cello), and piano trio (piano, violin, cello). The chamber orchestra, usually with fewer than 25 musicians, is often used for 18th-century music and usually requires a conductor. Seealso sonata.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

bubble chamber

Subatomic-particle detector that uses a superheated liquid which boils into tiny bubbles of vapour along the tracks of the particles. As charged particles move through the liquid, they knock electrons from the atoms of the liquid, creating ions. If the liquid is close to its boiling point, the first bubbles form around these ions. The observable tracks can be photographed and analyzed to measure the behaviour of the charged particles. Developed in 1952 by Donald Glaser, the bubble chamber proved very useful in the 1960s and '70s for the study of high-energy nuclear and particle physics.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.