"We only put it there
To give warning of something we dare not
Ignore, lest we should come upon it
Too suddenly, recognise it too late,
As our cries were swallowed up and all hands lost.”
W. S. Merwin
The Fog-horns on our homepage
The large black fog-horns that can be seen in front of the lighthouse were installed at The Lizard in 1878. Because they were the last compressed air fog signal in Britain to be discontinued, there workings are still functional and are sounded on special occasions. During thick and foggy weather, one blast will be sounded every five minutes. This was later changed to two blasts (high, low) every two minutes, later altered again on October 8th, 1908, to two blasts (long blast; short blast) in succession every minute.
Audible fog signals have been used in one form or another for many hundreds of years. In their infancy bells or gongs were struck manually, following that small cannons fired at regular intervals were sometimes used to warn away ships. You can imagine how impractical this became when fog conditions persisted over several days!
Most fog-horns of this type use a vibrating column of air to create an audible tone, but the method of setting up this vibration differs. Some horns, like the Daboll trumpet, used vibrating plates or metal reeds, a similar principle to a modern electric car horn. Others utilised air forced through holes in a revolving cylinder or disk, in the same manner as a siren. Some later fog bells were placed under water, particularly in especially dangerous areas, so that their sound would be carried further and reverberate through the ship’s hull.
At the turn of the century, experiments to develop more effective fog-horns were carried out by John Tyndall and Lord Rayleigh, amongst others. Lord Rayleigh’s ongoing research for Trinity House culminated in a siren with a large trumpet designed to achieve maximum sound propagation.
As two Signalman owners can attest, to sleep in The Lizard youth hostel pre ‘98 when the fog-horns sound will result in a sleepless night. Now with the sophisticated electronic siren (100 dB with a range of 4 miles) all you can hear is a gentle peep.