压缩空气
Industrial use of piped compressed air for power transmission was developed in the mid 19th century; unlike steam, compressed air could be piped for long distances without losing pressure due to condensation. An early major application of compressed air was in the drilling of the Mont Cenis Tunnel in Italy and France in 1861, where a 600 kPa (87 psi) compressed air plant provided power to pneumatic drills, increasing productivity greatly over previous manual drilling methods. Compressed air drills were applied at mines in the United States in the 1870s. George Westinghouse invented air brakes for trains starting in 1869; these brakes considerably improved the safety of rail operations. In the 19th century, Paris had a system of pipes installed for municipal distribution of compressed air to power machines and to operate generators for lighting. Early air compressors were steam-driven, but in certain locations a trompe could directly obtain compressed air from the force of falling water.