Pneumatic Dispatch
propulsion by means of compressed air or by forming a vacuum. Pneumatic railways have thus far proved abortive, but propulsion by compressed air has of recent years been successfully applied to a variety of practical uses. Parcels are thus conveyed, and internal communication in warehouses, hotels, etc., is carried on by its means. The most developed application of compressed air as a motive compressed force is in connection with the telegraph service of large cities. Pneumatic dispatch, which has proved a most useful auxiliary in securing prompt and cheap collection and distribution of telegraphic messages, was first introduced in London Pneumatic tubes are in use in Liver pool, Manchester, Glasgow, Dublin, etc.
The circuit system, but not with a continuous current, current, is extensively used in Paris. The tubes are of iron two feet in diameter. Trains leave the central station at fixed intervals and make the circuit. Other European cities have similar systems. New York, Philadelphia, and other American cities use a pneumatic mail dispatching system.
This is being superseded to some extent (1920) by swift motor vehicles.