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harmonium:see reed organreed organ,
an organ in which air is forced over free reeds by means of bellows, usually worked by pedals. It is played by the use of one or more keyboards. Variations in tone are produced by stops that control different sets of reeds or vary the manner in which the air acts
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a keyboard wind instrument. The harmonium was invented in the second decade of the 19th century; its precursor was the orgue expressif designed by the Frenchman G. J. Grenié in 1810. A similarly constructed instrument was created in 1818 by the master A. Häckel. The modern harmonium resembles a small upright piano; it has a piano keyboard, with six to 20 registers activated by movable levers. The keyboard is divided into a left side, with a range from C two octaves below the bass staff to E at the bottom of the treble staff, and a right side, with a range from F at the bottom of the treble staff to C two octaves above the treble staff. Sound is produced when air passes over steel tongues set in brass frames, causing the tongues, which act as free reeds, to vibrate. Air is pumped through channels to the reed compartments by pedal-operated bellows. The sound of the harmonium is similar to that of the organ.