An Eolian harp. A box fitted with strings, like a fiddle. The strings, however, are not sounded by a bow, but by a current of air or wind passing over them.
Awake, Eolian harp, awake, And give to rapture all thy trembling strings.
Gray: Progress of Poetry, lines 1, 2.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894