Foghorns: Robert Foulis's Stolen Steam Horn, Sirens, and the Diaphone Grunt

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Before foghorns, keeping ships off the rocks in fog meant conch shells, gongs, bells, and cannon. Trinity House favored explosive signals, and its Signal Fog Mark I had keepers at places like Portland Bill wire and fire two gun cotton charges every five minutes for as long as the fog lasted. In 1837 Maine even tried a machine struck triangle with four foot sides. The breakthrough came from Robert Foulis, a Scottish immigrant in Saint John, New Brunswick, who walked home through fog, heard only the low notes of his daughter's piano, and realized low frequency sound travels through moisture that scatters high notes. He designed a steam powered horn with coded blasts, but the Bay of Fundy lighthouse commissioners rejected it, and his plans reached engineer T.T. Vernon Smith, whose name was on the horn built on Partridge Island in 1859.

Foulis won a legislative inquiry that credited him as inventor, but he never patented the horn and never profited. American lighthouses adopted Celadon Leeds Daboll's coal powered reed trumpet, while John Tyndall and Lord Rayleigh tested sirens for Trinity House. A 1913 reporter at Trevose Head in Cornwall compared one to an army of panthers and the roar of a thousand mad bulls. The diaphone, adapted from Robert Hope-Jones's pipe organ stop by John Northey of Toronto, became the standard, its closing grunt made by a slowing piston. Big horns were replaced in the 1960s and 1970s, and lighthouse authorities now call long range foghorns obsolete.

• Turkish ships were historically exempt from rules requiring bells because Islamic law then forbade them.
• Clockwork coders opened the valves in set rhythms so blind mariners could match a signal to a chart.
• Underwater bells, such as at White Shoal Light in Michigan, rang codes that ships heard through water filled receivers in their hulls.
• In 1982 Dutch broadcaster VPRO aired a live concert mixing foghorns from Emden, Calais, Den Helder, and Marken with music by Alvin Curran.
• Modern horns are triggered when fog reflects a lighthouse's own light beam back to a sensor.