SUBMARINE SIGNALING. Submarine signaling is the art of producing sound waves In water and of transforming them into air waves so that they can be heard.
The art of submarine signaling has been directed entirely toward safeguarding lives and property at sea. Sound waves can be trans mitted through water from a suitable source of sound and heard with well designed receiving apparatus at greater distances and with greater certainty than is possible through air with any sound-making device that has ever been pro duced. This fact gave the incentive to those who originally undertook the development of this art. Later, as the knowledge of submarine eds.:A, it has become possible to determine with considerable accuracy, from a ship moving or at rest, the direction from which the sound is coming and even the distance be tween the ship and the sound-producing de vice. Moreover, the receiving devices have been so far perfected that it is not necessary that the source of sound should be made artificially. The receiving devices can now be made in such a way that the noises of invisible ships moving through the water can be heard and the posi tion of the moving ship relative to the listener ascertained. With the latest forms of sub marine signaling devices it is possible to send and receive telegraph messages transmitted by sound waves through the water. It must he appreciated that no wires connect the sending and receiving stations. Submarine signaling is wireless communication using compressional or sound waves in water as the means rather than the transverse ether waves used to-day in what is commonly called wireless transmission.
History.—It had been well known for nearly 75 years that sound waves were transmitted through water in the same manner as through air, but to greater distances and with greater velocity (velocity of sound waves in air about 1,040 feet per second; in sea water about 4,900 feet per second). A number of inventors prior to about 1900 had suggested or patented de vices for making or detecting submarine sounds. No consistent or real progress was made until in 1898 a group of investigators attacked the problem. These investigators and their suc cessors, associated in the Submarine Signal Company, have carried the art to its present high degree of usefulness. A few of those
who have made material contributions to the advancement of the art are Arthur J. Mundy, Elisha Gray J. B. Millet, Lucian I. Blake, E. C. Wood and 'Reginald A. Fessenden.
Receiving Devices.— The earliest sound re ceiving device for use in water was employed by Colladon and Sturm in experiments made by them in Lake Geneva in 1823. The sound receiver was a large ear trumpet, the small end of which was placed in the observer's ear. The large end was closed with a thin plate and was placed under water. Modifications of this early form are in successful service to-day, but the receiver most commonly used to-day is an elec trical current varying device similar in principle to the telephone transmitter generally used on land lines.
One of the problems in 'submarine signaling which has been most difficult of solution was to find a way by which the sound-receiving de vice should be responsive to the noises pro duced by the distant source and, at the same time, would be insensitive or non-responsive to the noises produced by the impact or move ment of the surface waves of the water on the sides of a moving ship, and by the noises of the machinery within the ship. Innumerable means have been suggested for eliminating these foreign disturbing noises called "water noises." Success has been attained by the use of a properly designed microphone element or "button" mounted in a special form of water tight case, Fig. 1, and, when used on ship board, by suspending the microphones in tanks, filled with water or other suitable fluid. These tanks are located within the ship below the water line and are so arranged that the fluid is in contact with the skin of the ship. It has been found that the sound waves from a dis tant source pass through the steel or iron skin of the ship with but little loss from re flection or absorption and, as a consequence, the sound waves from the distant source can ;,e easily heard. Furthermore, by this arrange ment the water noises are reduced to a mini mum as the ship passes through the water with the least possible disturbance.