Early fog signals at
Fort Point Light Station,
Maine Audible fog signals have been used in one form or another for hundreds of years, initially simply
seashell horns,
fog bells or
gongs struck manually. At some
lighthouses, a small
cannon was let off periodically to warn away ships, but this was labor-intensive and dangerous. 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.
Mechanization at the
Lizard Lighthouse,
Cornwall lighthouse foghorn (
Shetland) 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. Captain James William Newton in England claimed to have been the inventor of the fog signalling technique using loud and low notes. The development of fog signal technology continued apace at the end of the 19th century. 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. 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), installed in
Trevose Head Lighthouse,
Cornwall in 1913. One reporter, after hearing a steam-powered siren for the first time, described it as having "a screech like an army of panthers, weird and prolonged, gradually lowering in note until after half a minute it becomes the roar of a thousand mad bulls, with intermediate voices suggestive of the wail of a lost soul, the moan of a bottomless pit and the groan of a disabled elevator." Some later fog bells were placed underwater, 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). This was an earlier precursor to
RACON.
Diaphone From the early 20th century an improved device called the
diaphone, originally invented as an
organ stop by
Robert Hope-Jones Obsolescence , where the fog signal was discontinued in 1966 Since automation of lighthouses became common in the 1960s and 1970s, most older foghorn installations have been removed to avoid the need to run their complex machinery, and have been replaced with electrically powered diaphragm or
compressed air horns. Activation is completely automated: a laser or photo beam is shot out to sea, and if the beam reflects back to the source (i.e., the laser beam is visible due to fog or precipitation), the sensor sends a signal to activate the foghorn. In many cases, modern navigational aids, including
GPS, have rendered large, long-range foghorns completely unnecessary, according to the
International Association of Lighthouse Authorities. ==References==