A Fog signal is a device used in fog to produces an audible warning, and sometimes a visual one too, indicating to a vehicle the presence of a hazard. There are commonly two circumstances where they are used.

Marine fog signals

Ships and lighthouses warn of their presence in foggy conditions. Until the end of the Nineteenth century this was done variety of means, including gunfire, explosions, bells and steam whistles. However these were gradually replaced by foghorns invented in the 1850s. The replacement was slow in some cases, for example the Fastnet Rock Lighthouse had an explosive fog signal installed as late as 1883 which electrically detonated a small charge of guncotton every five minutes. Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ... This page is about the navigational aid called foghorn, for the Ray Bradbury science fiction novel, see The fog horn Foghorns near Lizard Point, Cornwall Foghorns are a navigation aid for mariners. ... Events and Trends Technology Production of steel revolutionised by invention of the Bessemer process Benjamin Silliman fractionates petroleum by distillation for the first time First transatlantic telegraph cable laid First safety elevator installed by Elisha Otis Science Charles Darwin publishes The Origin of Species, putting forward the theory of evolution... Fastnet Rock (51° 23. ... 1883 was a common year starting on Monday (see link for calendar). ... Nitrocellulose (Cellulose nitrate, guncotton) is a highly flammable compound formed by nitrating cellulose (e. ...

Railway fog signals

Fog signals have also been used on railway lines since the middle of the Nineteenth century to indicate to the driver of a moving train that a broken down train, a working party or some other unforeseen hazard is on the line ahead. They are small explosive detonators which are placed on the track and detonated by the pressure of the wheels of the oncoming train. The loud report of the explosion provides the indication to the driver. This article is concerned solely with chemical explosives. ... A detonator is a device used to trigger bombs, shaped charges and other forms of explosive material and explosive devices. ...