AUTOMATIC FOG SIGNALS

Shannon News, 9 August 1927, Page 4

AUTOMATIC FOG SIGNALS

In view of the increasing use of wireless beacon stations for the protection of mariners in foggy weather, it is interesting to note that a most ingenious form of automatic fog-sig-aalling apparatus has been in operation in Dublin Bay for nearly two years. The controlling medium in this case is not wireless but light, which may however, be regarded as a type of short-wave energy. A ray of light is kept constanttly focussed, over a distance of about a mile, upon an optically sensitive cell, located in the distant signalling apparatus. Under normal condtions the signalling apparatus remains inactive. The occurrence of fog however, automatically reduces the effect of the light ray on the sensitive cell. When visibility is reduced to a dangerous degree, the resistance of the sensitive cell reaches a point where the current in a local circuit falls to hold apart the contact points of a relay circuit. The latter is accordingly energised, and immediately operates to sound a warning fog-sig-nal.