Fog bell

Starting in the 18th century, fog signals were given for seafaring in Europe, initially cannons or guns.

[2] These were initially rung by hand, which was a chore during prolonged fog,[1] others used mechanisms similar to clockwork that had to be wound periodically.

[5] Sound buoys are mainly suitable as safe water marks for the entrances of nautical channels from the sea.

Experiments with bells underwater were first undertaken in 1826 in Lake Geneva by Charles-François Sturm and Jean-Daniel Colladon to determine the speed of sound.

In the late 19th century, bells began to be installed on lightvessels below the surface of the water, the sound of which was received by ships in the fog using stethoscopes or microphones.

However, the bells were soon replaced by electric transducers, and the ideas of subsurface sound generation and detection were used by Reginald Fessenden to develop sonars.

[13][14][15][16][17] In the free nautical chart OpenSeaMap, 175 seamarks with bells as fog signals have been entered by volunteers, compared to 12 gongs, 14 diaphones, 99 whistles, 103 sirens and 787 foghorns (as of April 2024).

Eliot references fog bells several times, in keeping with the varied nautical images used throughout the poem.

In Part II, Eliot again references the "undeniable clamour of the bell of the last annunciation" heard by unidentified mariners as their boat drifts, slowly leaking.

Finally, in Part IV, a prayer to the Blessed Virgin Mary, Eliot likens a fog bell to a "perpetual Angelus".