A clock which plays a tune at the hours or at certain specific hours, (e.g. 3, 6, 9 and 12 o'clock). The name is also sometimes given to clocks with musical chimes only. The musical movements of clocks fall into three categories, in all of which the tune is played by a revolving barrel, occasionally a wheel, set with metal pins. In the first type pins activate hammers to play a carillon on bells, in the second the pins play a tune directly on a steel comb, and in the third (organ clocks) pins or metal bridges control the supply of air from bellows to pipes. Musical-box movements and organ clocks were both popular in the 18th century when certain composers of note wrote tunes for such toys. In the 19th century the trade in automata and musical boxes, including those incorporated in clocks, passed almost wholly to the Swiss.