An aeolian harp (or æolian harp or wind harp) is a musical instrument that is “played” by the wind.
It was very popular as household instruments during the Romantic Era, but is only being hand-crafted today. The reason of its disappearing is its weak sound overpowered by the background noise of industrial revolution.
Its fascinating sound inspired many composers: from the Chopin’s Etude num. 1 op. 25 (here performed byOlaf Schmidt), that is sometimes called the “Aeolian Harp” etude, a nickname given it by Robert Schumann, to the Henry Cowell’s work. His Aeolian Harp (1923) was one of the first piano pieces ever to feature extended techniques which included plucking and sweeping the pianist’s hands directly across the strings of the piano. Other Cowell works that use this technique include: The Sword of Oblivion (1920-1922), The Banshee (1925), Duett to St. Cecilia (1925), The Sleep Music of Dagna (1926), The Fairy Bells (1928), The Leprechaun (1928), The Fairy Answer (1929), and Irish Epic Set (1946).

The traditional aeolian harp is essentially a wooden box including a sounding board, with strings stretched lengthwise across two bridges. It is placed in a slightly opened window where the wind can blow across the strings to produce sounds. The strings can be made of different materials (or thicknesses) and all be tuned to the same note, or identical strings can be tuned to different notes.
Here we have an example of a vertical aeolian harp built by Ralf Kleemann who is also a professional harpist, and one by Roger Winfield who builds instruments and also produces CDs..