bellows, expansible, gas-tight chamber used to pump or store a gas. One of the simplest and most familiar types of bellows is the manual one used for providing a forced draft to a fire. The expansible chamber consists of a leather bag with pleated sides. The bag is fixed between handles in such a way that they can be used to make it expand and contract. The inlet and outlet vents are provided with valves so that air must enter through the first and leave through the second. The device thus comprises a simple air pump. One of the major uses of the bellows has been to provide a draft for fires that are used to help extract a metal from its ore. In a device such as an aneroid barometer a small bellows is filled with a known amount of gas that expands and contracts in response to changes in external pressure. This small bellows is coupled to some form of indicating or recording device. Another use of the bellows has been to provide wind for such musical instruments as the accordion and older pipe organs.