Small rectangular wind instrument consisting of free metal reeds set in slots in a small wooden frame and blown through two parallel rows of wind channels. Successive notes of the diatonic (seven-note) scale are obtained by alternately blowing and sucking; the tongue covers channels not required. In chromatic (12-note scale) models, a finger-operated stop selects either of two sets of reeds tuned a semitone apart. The harmonica was invented in 1821 by Friedrich Buschmann (1805–64) of Berlin, who borrowed the basic principle from the Chinese sheng. It is widely used in blues as well as folk music and country music.