the barrel organ with the steam organ or calliope. In the United Kingdom barrel pianos, particularly those played in the streets, are frequently called barrel organs. Barrel The pieces of music (or tunes) are encoded onto the barrel using metal pins and staples. Pins are used for short notes, and staples of varying lengths for longer notes. Each barrel usually carried several different tunes. Pinning such barrels was something of an art form, and the quality of the music produced by a barrel organ is largely a function of the quality of its pinning. The organ barrels must be sturdy to maintain precise alignment over time, since they play the same programming role as music rolls and have to endure significant mechanical strain. Damage to the barrel, such as warpage, would have a direct (and usually detrimental) effect on the music produced. The size of the barrel will depend on the number of notes in the organ and the length of the tune to be played. The more notes, the longer the barrel. The longer the tune, the greater the diameter. Since the music is hard-coded onto the barrel, the only way for a barrel organ to play a different set of tunes is to replace the barrel with another one. While not a difficult operation, barrels are unwieldy and expensive, so many organ grinders have only one barrel for their instrument. Operation A set of levers called keys is positioned just above the surface of the barrel. Each key corresponds to one pitch. A rod is connected to the rear of each key. The other end of the rod is a metal pin which operates a valve within the wind chest. When the instrument is played (by turning the crank), offsets on the crank shaft cause bellows to open and close to produce pressurized air. A reservoir/regulator maintains a constant pressure. A worm gear on the crank shaft causes the barrel to rotate slowly and its pins and staples lift the fronts of the keys. This causes the other end of the key to press down on the end of the rod which, in turn, activates the valve and allows air from the bellows to pass into the corresponding pipe. To allow different tunes to be played from one barrel, the barrel can be moved laterally to bring a different set of pins and staples under the keys. Street