The prototype of modern coastal fog signals was the mediaeval warning bell. The most famous example was that which graced the legendary Inchcape Rock, a dangerous reef, covered at every tide, that lies adjacent to Arbroath near the Firth of Tay in Scotland.
The story goes that many centuries ago the Abbot of Arbroath, or Aberbrothok as it was known in the vernacular, ordered a bell to be fixed on a timber float and anchored to the rock as an acoustic aid to sailors passing by. As Robert Southey put in his wellknown ballad:
Then they knew the perilous rock
And blessed the Abbot of Aberbrothok.
But vandalism, alas, was rife in those days, too. Shortly afterwards a pirate chief called Ralph the Rover cut the bell adrift, only to be wrecked himself upon the self-same rock a year later, a victim of his own misdeed. Southey again tells us what happened, and Ralph's reaction, when the event occurred:
The vessel strikes with a shivering shock.
O Christ! It is the Inchcape Rock!
The Abbot's bell was high-tech for its time. In the very early days of seafaring, any crude device for making noise was a help to sailors trying to navigate in fog. Fishermen's wives, waiting ashore for husbands to return, would create a din with cookingpans, or whistle through the mist to guide their menfolk home.
Sailors themselves would shout and listen for the echoes through the fog to judge their distance from any nearby cliffs or headlands. Pounding drums were used to guide the Vikings safely into harbour, and the Imperial Gong was an honoured navigational aid in ancient China.
With the invention of gunpowder, and for many centuries thereafter, cannons ashore were often used to sound a warning, one of the most famous being the gun which, from 1719 onwards, boomed at half-hourly intervals over Boston harbour. Manually operated fog-bells were also common during the early 1800s, and as the century progressed the Victorians used their ingenuity to equip many of these with mechanical strikers of the cleverest design.
The 1850s saw the development of a new kind of fog signal, a horn in which compressed air was used to vibrate a diaphragm or reed. And from this it was only a short step to the device still in common use today, the diaphone. Early versions of the diaphone were supplied with compressed air by means of steam engines, and in a spell of foggy weather the hungry monsters had to be fed great quantities of coal, some of them as much as two tons per day.