compost Mass of rotted organic matter made from decomposed plant material. It is used in agriculture and gardening generally to improve soil structure rather than as a fertilizer, because it is low in plant nutrients. When properly prepared, it is free of obnoxious odours. Composts com¬ monly contain about 2% nitrogen, 0.5-1% phosphorus, and about 2%
potassium. Lime and nitrogen fertilizers and manure may be added to speed decomposition. The nitrogen of compost becomes available slowly and in small amounts. Because of their low nutrient content, composts are applied in large amounts.
compound Any substance composed of identical molecules consisting of atoms of two or more elements. Millions are known, each unique, with unique properties. Most common materials are mixtures of compounds. Pure compounds can be obtained by physical separation methods, such as precipitation and distillation. Compounds can be broken down into their constituents to various degrees or changed into new compounds by chemi¬ cal reactions. Atoms always combine into molecules in fixed proportions, distinguishing compounds from solutions and other mechanical mixtures. Compounds are often classified as inorganic and organic compounds; coor¬ dination complexes, which contain metal atoms (usually transition ele¬ ments) bonded to ligands that may be organic, are somewhat in between. Compounds may also be classified by whether they have ionic or cova¬ lent bonds (many include both types).
comprehension Act of or capacity for grasping with the intellect. The term is most often used in connection with tests of reading skills and lan¬ guage abilities, though other abilities (e.g., mathematical reasoning) may also be examined. Specialists in administering and interpreting such tests are known as psychometricians (see psychometrics) or differential psy¬ chologists. See also dyslexia; laterality; psychological testing; speech.
compressed air Air reduced in volume and held under pressure. Force from compressed air is used to operate numerous tools and instruments, including rock drills, train brake systems, riveters, forging presses, paint sprayers, and atomizers. Bellows have been used since the Early Bronze age to provide air for smelting and forging. The 20th century witnessed a large increase in the use of compressed-air devices. The introduction of jet engines for military and passenger aircraft stimulated the use and improvement of centrifugal and axial-flow compressors. Digital-logic pneumatic-control components (developed in the 1960s) can be used in power and control systems (see pneumatic device).
compression ratio Degree to which the fuel mixture in an internal- combustion engine is compressed before ignition. It is defined as the vol¬ ume of the combustion chamber with the piston farthest out divided by the volume with the piston in the full-compression position (see piston and cylinder). A compression ratio of six means that the action of the pis¬ ton compresses the mixture to one-sixth its original volume. A high ratio promotes efficiency but may cause engine knock.
compressor Machine for increasing the pressure of a gas by mechani¬ cally decreasing its volume. Air is the most frequently compressed gas, but natural gas, oxygen, nitrogen, and other industrially important gases are also frequently compressed. There are three general types of compres¬ sors. Positive-displacement compressors are usually of the reciprocating piston type (see piston and cylinder), useful for supplying small amounts of a gas at relatively high pressures. Centrifugal compressors are particu¬ larly suited for compressing large volumes of gas to moderate pressures. Axial compressors are used for jet aircraft engines and gas turbines.
Compromise of T 850 Series of measures passed by the U.S. Con¬ gress to settle slavery issues and avert secession. The crisis arose in late 1849 when the territory of California asked to be admitted to the Union with a constitution prohibiting slavery. The problem was complicated by the unresolved question of slavery’s extension into other areas ceded by Mexico in 1848. In an attempt to satisfy pro- and antislavery forces. Sen. Henry Clay offered a series of measures that admitted California as a free state, left the question of slavery in the new territories to be settled by the local residents, and provided for the enforced return of runaway slaves and the prohibition of the slave trade in the District of Columbia. Sup¬ port from Daniel Webster and Stephen A. Douglas helped ensure passage of the compromise. Moderates throughout the Union accepted the terms, which averted secession for another decade but sowed seeds of discord.
Compromise of 1867 or Ausgleich Vaus-.gllkX Compact that established the dual monarchy of Austria-Hungary. The kingdom of Hun¬ gary desired equal status with the Austrian empire, which was weakened by its defeat in the Austro-Prussian War of 1866. The Austrian emperor Francis Joseph gave Hungary full internal autonomy, together with a responsible ministry, and in return it agreed that the empire should still be a single great state for purposes of war and foreign affairs, thus main¬ taining its dynastic prestige abroad.
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Compton effect ► computer graphics I 443
Compton effect Change in wavelength of X rays and other energetic forms of electromagnetic radiation when they collide with electrons. It is a principal way in which radiant energy is absorbed by matter, and is caused by the transfer of energy from photons to electrons. When pho¬ tons collide with electrons that are free or loosely bound in atoms, they transfer some of their energy and momentum to the electrons, which then recoil. New photons of less energy and momentum, and hence longer wavelength, are produced; these scatter at various angles, depending on the amount of energy lost to the recoiling electrons. The effect demon¬ strates the nature of the photon as a true particle with both energy and momentum. Its discovery in 1922 by Arthur Compton was essential to establishing the wave-particle duality of electromagnetic radiation.
Compton, Arthur (Holly) (b. Sept. 10, 1892, Wooster, Ohio, U.S.—-d. March 15, 1962, Berkeley, Calif.) U.S. physicist. He taught at the University of Chicago (1923—45) and later served as chancellor (1945-54) and professor (1953-61) at Washington University. He is best known for his discovery and explanation of the Compton effect, for which he shared with C.T.R. Wilson the 1927 Nobel Prize for Physics. He was later instrumental in initiating the Manhattan Project, and he directed the development of the first nuclear reactors.
Compton-Burnett, Dame Ivy (b. June 5, 1884, Pinner, Middlesex, Eng.—d. Aug. 27, 1969, London) British novelist. She graduated from the University of London and published her first novel, Dolores, in 1911. Her second, Pastors and Masters (1925), introduced the style— employing clipped, precise dialogue to reveal her characters and advance the plot—that made her name. Her novels often dealt with struggles for power: Men and Wives (1931) featured a tyrannical mother, A House and Its Head (1935) a tyrannical father. She was created Dame of the British Empire in 1967.
computational complexity Inherent cost of solving a problem in large-scale scientific computation, measured by the number of operations required as well as the amount of memory used and the order in which it is used. The result of a complexity analysis is an estimate of how rapidly the solution time increases as the problem size increases, which can be used to analyze problems and assist in the design of algorithms for their solution.
computational linguistics (CL) Use of digital computers in unguis- tics research. The simplest examples are the use of computers to scan text and produce such aids as word lists, frequency counts, and concordances. From the mid-1950s to the mid-1960s progress was made by research groups working on machine translation and information retrieval. Theo¬ retical CL deals with formal theories about linguistic knowledge, which today have reached a degree of complexity that can only be managed using powerful computers. Applied CL focuses on practical results of modeling human language use.