Keyboard instrument in which pressurized air produces notes by means of a series of tuned pipes. The simplest organs consist of a single rank of pipes, each corresponding to a single key. They are arranged over a wind chest connected to the keys by a set of valves and fed with a supply of air by electrically or mechanically activated bellows. By pulling out knobs, called stops, the player engages new ranks of pipes. Two distinct types of pipes are used: flue pipes (both open and stopped) produce sound by directing air against the edge of an opening in the pipe, whereas reed pipes sound by means of a thin metal tongue inside the pipe that vibrates against a fixed projection next to it. A large organ may have five or more banked keyboards, or manuals, each of which controls a distinctive group of pipes. Most organs also have pedalboards played with the feet. A large organ's pipes may vary in length from about 1 in. to 32 ft (2.5 cm to 10 m), resulting in a huge nine-octave range. The earliest organ (circa 250 BC) was the Greek hydraulis, in which the wind was regulated by water pressure. The bellows-fed organ appeared about the 7th century AD. The organ became firmly associated with the church by the 10th century. As organs became widespread, different regions pursued different modes of construction and sought different tonal ideals. The Baroque German organ is ideally suited to polyphony, while the French taste for variety of timbres eventuated in Aristide Cavaillé-Coll's vast “orchestral” organs. Seealso harmonium.

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National monument, southwestern Arizona, U.S., at the Mexican border. It was established in 1937. With an area of 330,689 acres (133,929 hectares), it preserves segments of the mountainous Sonoran Desert and is named for the organ-pipe cactus. Wildlife includes Gila monsters, antelope, coyotes, and a variety of birds.

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(born Jan. 1, 1879, London, Eng.—died June 7, 1970, Coventry, Warwickshire) British writer. Forster was born into an upper-middle-class family. He attended the University of Cambridge and from roughly 1907 was a member of the informal Bloomsbury group. His early works include Where Angels Fear to Tread (1905), The Longest Journey (1907), A Room with a View (1908), and his first major success, Howards End (1910), novels that show his acute observation of middle-class life and its values. After periods in India and Alexandria, he wrote his finest novel, A Passage to India (1924), examining the failure of human understanding between ethnic and social groups under British rule. Maurice, a novel with a homosexual theme written in 1913, appeared posthumously. Aspects of the Novel (1927) is a classic discussion of aesthetics and the creative process. Awarded an honorary fellowship in 1946 at Cambridge, he lived there until his death.

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See Pipe organ