Forty Years On The Pacific/Submarine Signals
A NEW device for the protection of steamers in foggy weather is the submarine signal, with which a great many passenger vessels are equipped. It consists of a telephone in the pilot house, which is connected with a tank, placed as low as possible in the vessel's hold on each side of the bow. From each tank there is a dictaphone supplied by a dry battery, which carries the sound to the telephone. On shore, light-vessels, buoys or prominent point a submarine bell is installed at from twenty-five to thirty-five feet below water. This bell is struck by electricity or compressed air—a code of strokes being used to distinguish different stations. Water, being a better conductor of sound than air, conveys the stroke of the bell distinctly.
In foggy weather, the captain of the steamer, when approaching land, and in vicinities of submarine bells, can go into the pilot house and on placing the phone to his ear can hear these signals from five to fifteen miles off. If the bell should be right ahead, it will be heard distinctly in both receivers, but if on one side, it will be heard in only one receiver. To bring the signal ahead, the vessel has to swing around to bring the sound in both receivers. This device is invaluable to mariners in foggy weather on rock-bound coasts.