A branch of engineering in which pressurized air or other gas is used to perform useful work, dating from the work of Hero of Alexandria (c. ad 10–70), the Greek mathematician and engineer who described machines powered by steam or the wind. In modern applications an electric motor drives a compressor and the compressed gas works pistons or other devices. Pneumatic systems are used for many purposes, including air brakes on large vehicles such as buses, trucks, aircraft, and trains, and on dental drills, pneumatic road drills, jackhammers, and pipe organs.