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This page is about the navigational aid called foghorn, for the Ray Bradbury Science Fiction short story, see " The Fog Horn ". For the cartoon character, see Foghorn Leghorn . , Cornwall ]]Foghorns are a Navigation aid for Mariners . In Fog gy conditions, when visual navigation aids such as Lighthouse s are obscured by the Weather , fog horns provide an Audible Warning of Rocks , Headlands , or other dangers to shipping. The first Automated Steam -powered fog horn was invented by Robert Foulis of Saint John , New Brunswick , Canada . The first model was installed on Partridge Island in 1859 , replacing the less effective Bell and Cannon which had been formerly used as warnings to ships in fog. The noise produced by a foghorn is very deep, due to the fact that deep sounds are audible to human ears at a greater distance than higher pitched ones. It is also very loud so ships a considerable distance away can heed its warning. Legend suggests that Robert Foulis heard his daughter playing piano in the distance on a foggy night, and noticed the low notes were more audible than the higher notes. All foghorns use a vibrating column of air to create an audible tone, but the method of setting up this vibration differs. Many older foghorns, especially those on land, used Diaphone s to create the audible sound, producing a distinctive, deep and penetrating tone followed by an all-too-audible 'grunt', resulting in the famous two-tone sound that most people acquaint with foghorns and the sea. Other horns used vibrating plates, similar to a modern electric car horn, or air forced through holes in a revolving cylinder, much in the same manner as a Siren . When diaphone foghorns were still being constructed, the U.S.A. lighthouses usually had a two tone horn. Such horns usually sounded an E♭ quarter note followed by an A♭ half or whole note. English-built foghorns were usually single-tone horns, producing a long single note, usually an F or a G. Many Canadian foghorns are single-tone. SEE ALSO EXTERNAL LINK
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