Ktesibios of Alexandria, in the 3d cent. B.C., invented the hydraulis, in which water pressure was used to stabilize the wind supply. The pipes were arranged in rows upon the wind chest and the air was permitted to enter any pipe at will by means of wooden sliders. The hydraulis was the prevailing organ for several centuries and reappeared at intervals throughout the Middle Ages.
Evidence of the first purely pneumatic organ is found on an obelisk erected at Byzantium before A.D. 393. Byzantium became the center of organ building in the Middle Ages, and in 757 Constantine V presented a Byzantine organ to Pepin the Short. This is the earliest positive evidence of the appearance of the organ in Western Europe. By the 10th cent., however, organ building had made considerable progress in Germany and England. The organ built c.950 in Winchester Cathedral is said to have had 400 pipes and 26 bellows and required two players and 70 men to operate the bellows.
The keyboard, or manual, was a creation of the 13th cent., making possible the performance of more complex music. The earliest extant music written specifically for organ, dating from the early 14th cent., gives evidence that by then the manuals of the organ had full chromatic scales, at least in the middle registers. Organs in the Middle Ages already had several ranks of pipes, each key causing a number of pipes to sound simultaneously. All were diapasons, or principals, the pipes of timbre characteristic only of the organ, and the various pipes controlled by one key were tuned to the fundamental and several harmonics of a given tone.
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