which would take up out of the water the signals arriving from neighboring vessels. As boys in swimming communicate the sound of the striking of stones together under water, so is it possible to send musical tones from one ship to another.
For steamships the sound-producing apparatus was designed to be a steam fog-horn or whistle, specially constructed to sound under water, and to be heard at least from six to eight miles. From the nature of its tone it would be easily distinguishable from other sounds always more or less present under water, such as from breakers, waves, etc. With such whistles a Morse alphabet of long and short blasts and pauses was to provide a means of extended communication, while a simple universal code would indicate a ship's course. Since ignorance of the very presence of a ship, rather than incorrect estimates of her course, has been the principal cause of ocean collisions, the simple hearing of the sound would prove a most excellent general safeguard. Bell-buoys were to have a second bell added under water, while lightships, lighthouses, and any headlands might also be provided with submerged bells which could be rung from the shore, when necessary. Sailing-craft, both large and small, would have bells; and, since an ordinary locomotive-bell can be heard, according to experiments, at least two miles under water, these simple means would seem to afford sufficient limits for protection for such vessels.
As to the receiving apparatus, with which each vessel was to be provided: The original plan of 1883, and which has not been changed, was to employ some form of telephone acting as a transmitter under water, and connected with a receiver within the vessel. The surface of the transmitter exposed to the water, and which must receive the sound-waves, should be protected against ice, barnacles, heavy waves, etc. One design was: One or more vertical pipes in different parts of a ship were to extend from the vessel's interior through the hull, near the keel, and be open to the free admission of water at their lower ends; their upper ends were to extend within the vessel a little way above the keel, and were to be plugged, so that the water could not overflow into the vessel. These pipes would then provide columns of water always still, and would communicate directly with the water outside. Sound would then enter and pass up these pipes, and would encounter microphonic transmitters placed suitably in them. Wires from the transmitters would run to a small room secluded where convenient in the ship, away from disturbing noises, and here telephone receivers would be placed, and observers stationed here in night or fog.
For small craft, it was found that a pipe shaped much like a powder-horn, with a thin, flexible membrane stretched tightly
