Hand-held harmonium

The pump organ, reed organ, harmonium, or melodeon is a type of free-reed organ that generates sound as air flows past a vibrating piece of thin metal in a frame. The piece of metal is called a reed.

More portable than pipe organs, free-reed organs were widely used in smaller churches and in private homes in the 19th century, but their volume and tonal range are limited, and they generally had one or sometimes two manuals, with pedal-boards being rare. The finer instruments have a unique tone, and the cabinets of those intended for churches and affluent homes were often excellent pieces of furniture. Several million free-reed organs and melodeons were made in the USA and Canada between the 1850s and the 1920s. During this time Estey Organ and Mason & Hamlin were popular manufacturers.

Christian Gottlieb Kratzenstein (1723–1795), professor of physiology at Copenhagen, was credited with the first free-reed instrument made in the Western world, after winning the annual prize in 1780 from the Imperial Academy of St. Petersburg. The harmonium's design incorporates free reeds and derives from the earlier regal. A harmonium-like instrument was exhibited by Gabriel Joseph Grenié (1756–1837) in 1810. He called it an orgue expressif (expressive organ), because his instrument was capable of greater expression, as well as of producing a crescendo and diminuendo. Alexandre Debain improved Grenié's instrument and gave it the name harmonium when he patented his version in 1840. There was concurrent development of similar instruments. A mechanic who had worked in the factory of Alexandre in Paris emigrated to the United States and conceived the idea of a suction bellows, instead of the ordinary bellows that forced the air outward through the reeds. Beginning in 1885, the firm of Mason & Hamlin, of Boston made their instruments with the suction bellows, and this method of construction soon superseded all others in America.

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