Bellows

A device that produces a controlled blast of air, built from a flexible bag of rigid boards joined by leather sides around an airtight chamber, with a valve that draws air in as the chamber expands and a nozzle that forces it out as the chamber is squeezed shut. The word descends from the Old English blaestbelig, blast-bag, later shortened to belig, bag, the same root as belly. Bellows were invented in antiquity, independently in more than one form, box bellows in East Asia, pot bellows in ancient Egypt, and accordion-style bellows in Europe, and their invention was a precondition for advances in iron smelting and welding that need a strong, controllable air blast. The double-acting piston bellows, which blows air on both the push and the pull of its handle rather than only one, gives a steadier and stronger blast; it is documented in China from at least the fifth century BC and reached Europe by the sixteenth century, letting smiths and smelters reach higher forge temperatures. The Greek inventor Ctesibius built a separate double-action piston bellows around 240 BC for lifting water, an independent invention for a different purpose. At the smith's forge, the bellows is what keeps the fire hot enough to work metal.