harmonica:1 The simplest of the musical instruments employing free reeds, known also as the mouth organ or French harp. It was probably invented in 1829 by Friedrich Buschmann of Berlin, who called his instrument the Mundäoline. The major production of the instrument has been in Germany since the early 19th cent. The reeds are set in a small, narrow case of wood or metal. For each reed there is a hole, through which the player draws or blows air with the mouth. Commonly the instrument is diatonic, having a compass of about two octaves, but the comparatively few virtuoso harmonica players use larger instruments having the full chromatic scale. The low cost and very small size of the harmonica adapt it well to class instruction among school children, and it is a common instrument in folk, rock, blues, and other forms of popular music. 2 Musical glasses, introduced in Dublin in 1743 by Richard Pockrich, played upon in London by Gluck in 1746, and improved by Benjamin Franklin c.1761; also called the glass harmonica. Franklin's instrument, which he called an armonica, consisted of a series of glass bowls, graduated in size and fitting one inside another. They were supported by a horizontal spindle passing through all of the bowls. As the spindle was made to revolve by means of a lever, the edges of the bowls passed through a trough filled with water. Contact of the player's fingertip with the moistened revolving edges of the bowls produced a penetrating, ethereal sound. A later form of the instrument had a keyboard. Both Mozart and Beethoven, as well as a few lesser composers wrote works for it. The instrument and the music for it has enjoyed a minor renaissance since the 1980s. 3 Strips of metal or glass, played upon with hammers or, later, having a keyboard, as described by Berlioz in his treatise on instrumentation. Related to this obsolete form are the celesta and glockenspiel.