Q HISTORY


of sounds, in terms of duration of the sound and the gap between sounds, which allowed mariners to know which signal site they were near. Whatever the truth, it has been low notes and distinct patterns of sound that have ruled the day, and much is certainly to the credit of Foulis. By 1870 trumpets, whistles, sirens and


bells had more or less all been perfected. Bells were not used in coastal areas except on buoys, while exposed coastal areas used steam whistles or sirens, trumpets being used in less exposed areas such as estuaries. Foghorns started to become the things we


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are familiar with following the invention of the diaphone at the beginning of the 20th century. Diaphones were complex, involving sleeves of brass which, when excited by steam or compressed air, vibrated rapidly back and forth in a chamber in the horn, producing a deep, throaty sound which both travelled further than sirens, and was much more acceptable to the public. They were, however, expensive to maintain. During the 1920s a cheaper and easier to


maintain form of foghorn came along in the shape of the diaphragm horn. This used two discs, both around six inches in diameter and 1/16th inch thick. One was secured while the other, with a hole in the centre, was free to vibrate, which it did when compressed air was passed between them. During the 1950s and 1960s trumpets,


sirens and whistles were phased out, leaving diaphones and diaphragm foghorns in service, until these started to be replaced by electronic diaphragm horns, which are basically very large loudspeakers. It was inevitable that the focus for the


development of fog signals was North America, especially on the eastern coasts of Canada and the United States. It’s to do with the weather. The Gulf Stream runs northwards along these coasts at some distance from land. The reverse Arctic Current runs southwards between the land and the Gulf Stream. When the wind blows from the east the warm moist air over the Gulf Stream is blown over the cold waters from the north, resulting in condensation and fog. The east coast of North America experiences a much greater frequency of marine fog than, say, the United Kingdom or Europe. Whereas historically many inventions


travelled west from Britain and Europe to the


Light beacon with foghorns at Albert Dock in Liverpool Americas, it seems the modern foghorn


travelled west to east. The June 1874 issue of The Nautical Magazine has an article about foghorns which says: “It is stated in a report made by a committee of the Trinity Brethren who visited the United States and Canada in 1872 that fog signals are used in America in the same way as lights and beacons in fine weather, and are trusted to almost as implicitly” and “It seems probable that ultimately some such system may come into practice on our own British coasts”. Indeed, this did happen. The report continues: “Trinity House,


therefore, sent out a committee to America to


see and hear what the instruments used in that country were like, and afterwards arranged for a lengthened series of experiments to be made with various instruments”. The article concludes that the benefits of such foghorns are beyond doubt. During the evolution of the modern fog


signal, some unusual solutions to fog warning


were experimented with, including: s In the 1950s a shore bell which responded to


the ship’s own bell and replied automatically s Echo boards, a little like mast-borne radar reflectors, which reflected back the sound from


ship-borne sound signals s A fog signal powered by the compressed air


captured in a natural blowhole s Underwater bells whose sound could be picked up by submarine microphones, taking advantage of the much greater speed and


range of sound underwater s Brown’s bell buoy, which incorporated a large open-bottomed tube with a whistle on top tethered to the sea floor. As the waves raised and lowered the water in the tube, the air was compressed and sounded the signal. Foghorns and other fog signals have


The first fog signal in America was a cannon installed at Boston Harbour in 1719


become almost redundant, partly because the enclosed superstructures of modern vessels make it difficult for anyone onboard to hear the warning, but mainly because modern navigational aids are now so good. However, it will be a sad day when the last long, deep, mournful moan is heard on the coast.


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