Frank Coffee, Forty Years On The Pacific — Submarine Signals (1920)
“ 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. ”
