What is foghorn?
Most often used in foggy conditions, is a device that uses sound to warn vehicles of hazards. Generally marine transport is using the term. When lighthouses are obscured the foghorn provides an audible warning of any dangers to ships. Robert Foulis created the first automated steam-powered foghorn. After hearing his daughter play piano in the fog, he realized the lower notes were more audible. So he designed a device to produce a low frequency sound. His fog signal was installed on Partridge Island in 1859; however, Foulis was in legal battles over his invention for the rest of his life. Celadon Leeds Daboll created a coal-powered foghorn that few lighthouses are using.
Foghorns use a vibrating column of air to create a tone although note all vibrations are resulting from the same method. Some use vibrating plates or metal reeds similar to a car horn. Others are similar to a siren where the air is entering through holes in revolving cylinder or disk. Semi-automatic foghorns work using a clockwork mechanism that opens the valve admitting air to the horns. Stevens Automatic Bell Striker was one of the first automated fog bells.
Through the use of laser beams the automated process works by detecting ships out at sea and if the beam reflects back the foghorn activates. Foghorns have also been used on railway lines in order to warn of dangers on the line.
History
udible fog signals have been used in one form or another for hundreds of years, initially simply bells or gongs struck manually.
At some lighthouses, a small cannon was let off periodically to warn away ships, but this had the obvious disadvantage of having to be fired manually throughout the whole period the fog persisted (which could be for several days). Lighthouse windows and lighting apparatus were susceptible to damage depending on the proximity of the explosion.[2] One incident of lax handling of explosives nearby resulted in a concussion that propelled the lighthouse keeper at Fort Amherst, who was seated, to the other end of the room.[3] In the United States, whistles were also used where a source of steam power was available, though Trinity House, the British lighthouse authority, did not employ them, preferring an explosive signal.
Throughout the 19th century efforts were made to automate the signalling process. Trinity House eventually developed a system (the "Signal, Fog, Mk I") for firing a gun-cotton charge electrically. However, the charge had to be manually replaced after each signal. At Portland Bill, for example, which had a five-minute interval between fog-signals, this meant the horns had to be lowered, the two new charges inserted, and the horns raised again every five minutes during foggy periods. Clockwork systems were also developed for striking bells.[4]
Mechanization
The first automated steam-powered foghorn was invented by Robert Foulis, a Scotsman who emigrated to Saint John, New Brunswick, Canada. Foulis is said to have heard his daughter playing the piano in the distance on a foggy night, and noticed the low notes were more audible than the higher notes: he then designed a device to produce a low-frequency sound, as well as a code system for use with it. Foulis repeatedly presented his concept to the Commissioners of Light Houses for the Bay of Fundy for installation on Partridge Island. While the Commissioners initially rejected Foulis's plan, one commissioner eventually encouraged Foulis to submit detailed plans to the Commission. For reasons unknown, the plans were given to another Canadian engineer, T. T. Vernon Smith, who officially submitted them to the Commissioners as his own. The foghorn was constructed at Partridge Island in 1859 as the Vernon-Smith horn. After protest by Foulis and a legislative inquiry, Foulis was credited as the true inventor, but he never patented or profited from his invention.[6]
The development of fog signal technology continued apace at the end of the 19th century.[7] During the same period an inventor, Celadon Leeds Daboll, developed a coal-powered foghorn called the Daboll trumpet for the American lighthouse service, though it was not universally adopted.[8] A few Daboll trumpets remained in use until the mid-20th century.
In the United Kingdom, experiments to develop more effective foghorns were carried out by John Tyndall and Lord Rayleigh, amongst others. The latter's ongoing research for Trinity House culminated in a design for a siren with a large trumpet designed to achieve maximum sound propagation (see reference for details of the Trials of Fog Signals[9]), installed in Trevose Head Lighthouse, Cornwall in 1913.
One of the first automated fog bells was the Stevens Automatic Bell Striker.[10]
Some later fog bells were placed under water, particularly in especially dangerous areas, so that their sound (which would be a predictable code, such as the number "23") would be carried further and reverberate through the ship's hull. For example, this technique was used at White Shoal Light (Michigan).[11][12] This was an earlier precursor to RACON.
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