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[[Image:Police whistles.jpg|thumb|250 px|Examples of police whistles]] | [[Image:Police whistles.jpg|thumb|250 px|Examples of police whistles]] | ||
Industrial whistles are used for [[Distress signal|signalling]] and | Industrial whistles are used for [[Distress signal|signalling]] and timekeeping both on railroad and [[ship]]s, and in [[factory|factories]]. Most of these whistles were [[steam power]]ed and not standardized. Individual [[locomotive]]s could be identified by their whistles. At noontime in industrial areas up into the 1950s whistles of every pitch could be heard, as each factory had a boiler and a whistle, if not full steam power. | ||
Railroads in particular used elaborate whistle codes for communication both within the [[train]] and with other trains. These methods are maintained today with motor-powered [[air horn]]s. Trucks also use air horns, especially since they often have air brakes and so there is already a source of compressed air on board. | Railroads in particular used elaborate whistle codes for communication both within the [[train]] and with other trains. These methods are maintained today with motor-powered [[air horn]]s. Trucks also use air horns, especially since they often have air brakes and so there is already a source of compressed air on board. |