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The «hydraulis» (organ) of Ktesibios
(the first keyboard instrument in the world)
It was the first worldwide keyboard instrument that was invented by Ctesibius in the 3rd century B.C.
It consisted of a) two pumps which supplied the air (of piston pump type), b) the "pnigeus" for the regulating of constant air pressure, g) the keyboard, and d) the musical pipes. The pumps were placed at both sides of the "pnigeus" and allocated non-return valves that were checked automatically by two bronze dolphins, while their pistons reciprocated with the help of hand levers. The "pnigeus" consisted of a cylindrical container with water which had a sunken inverted cone-shaped funnel fitted on holders at a small distance from its bottom. Two air supply pipes converged at the top of the funnel the while another pipe led the air with constant pressure to the collector of the keyboard. The stability of the air pressure was achieved due to the escaping of the redundant air from the bottom of the funnel and thus the stability of musical notes was ensured henceforth only depending on the length of the musical pipes ("auloi").
The keyboard consisted of 24 keys that checked the equal in number bronze air supply valves to 24 unequal in length musical pipes (like the hydraulis of the ancient Dion) which produced two complete octaves. The reintroduction of the keys-valves was achieved with the help of small flexible wooden boards (from the maple tree).
The hydraulis constitutes the forerunner of the contemporary church organ.
SOURCES: "Vitruvius, On Architecture, X", "Heron of Alexandria, Pneumatics, A 42".