with the exception of water organs, playing the organ before the invention of motors required at least one person to operate the bellows. when signaled by the organist, a "calcant" would operate a set of bellows, supplying the organ with wind. because calcants were expensive, organists would usually practise on other instruments such as the clavichord or harpsichord. by the mid-19th-century bellows were also being operated by water engines, steam engines or gasoline engines. starting in the 1860s bellows were gradually replaced by rotating turbines which were later directly connected to electrical motors. this made it possible for organists to practice regularly on the organ. most organs, both new and historic, have electric blowers, although some can still be operated manually. the wind supplied is stored in one or more regulators to maintain a constant pressure in the "windchests" until the action allows it to flow into the pipes.