The harmonium is a keyed instrument, like the piano or the organ, but on the piano
metallic cords and on the organ pipes produce the sounds. The sounds of the harmonium
are produced by a current of air passing through metallic reeds, causing them to vibrate.
The current is produced by bellows, which the player works with his feet (or with his
hands like an accordian as the Tea Party's model). According to the movement of the
bellows, the sounds become louder or softer (hence its name, the harmonium). It is
capable of more expression than the organ. The player is able to sustain the sounds in any
shade and degree of intensity as long as he pleases. Features and qualities which ensure
this instrument is decidedly advanced over the best piano: the tones of which are
strongest when the keys are first struck, and afterwards die away gradually.
As mentioned before, the accordion and concertina early on became associated with the folk tradition and lost favor among classical music lovers. However, not all free-reed instruments lost popularity. The harmonium (essentially a free-reed organ) is said to have been invented in 1842 by the Frenchman, Alexandre Debain (1809-1877), although its prototype, Kirsnik's Harmonica, appeared more than fifty years earlier.
By the second half of the nineteenth century the harmonium had evolved into a sophisticated instrument. The bellows were pumped by two foot pedals and the more expensive models had two keyboard manuals (each encompassing a range of five octaves) with up to thirteen stops (ranging from a sixteen foot Bourdon to a two foot Harpe eolienne), including tremolo and one or two knee-pedals to control volume. It was a popular instrument for churches which could not afford a pipe organ. In addition, it was favored for home music-making alongside the piano and in the cinema as a means of musical illustration in the era before sound films. Many nineteenth-century composers wrote serious music for the harmonium.