Every-day Science: Volume 7. The Conquest of Time and Space

by Henry Smith Williams; Edward Huntington Williams

The principle upon which this system is based is simply that of sound waves transmitted through the water and detected at a distance by a submerged electrical transmitter. The sound transmitted is usually that of a submerged bell. It is possible for a person whose head is submerged to hear the ringing of such a bell distinctly for a long distance; but of course for practical purposes such submergence is out of the question. The receiving apparatus of the Mundy-Gray signaling device offers a substitute in the form of a submerged "artificial ear"—an electrical transmitter, connected with a telephone receiver.

In the early experiments a small hollow brass ball filled with water and containing a special form of electrical transmitter was lowered over the side of a ship and connected by insulated wires to the receiver of a telephone in the pilot house. The sound of a submerged bell could be heard in this manner at a distance of ten or twelve miles. The location of the bell could be determined by having two such brass balls, one on each side of the hull of the vessel but not submerged to a depth below that of the hull, so that the ship itself acts as a screen in obstructing the sound waves coming from the bell. By listening alternately to the sounds of the bell transmitted through these two submerged balls it was found that the ball on the side of the ship toward the bell gave a distinctly louder sound. By turning the ship so that the sounds were of equal intensity the direction of the bell could be determined as either directly ahead or astern; and by using the compass the exact location could be determined.

But such brass-ball transmitters can be used only when the vessel is moving at a rate not exceeding three miles an hour. They are, therefore, of little value for ocean liners whose reduced speed far exceeds this. But the inventors discovered presently that by using the inside of the outer steel skin of the ship's hull below the water line as one side of the brass ball, the transmitter would work equally well. Indeed, with added improvements, this hollow metal device fastened to the inside of the hull on each side, with connecting wires leading to the pilot house, in its perfected form will pick up the sound of the submerged bell equally well at any speed, regardless of calm or storm.

The chief defect of this arrangement was that the sound of the pulsations of the engines of the ship were also heard, and interfered seriously with the detection of the sound of the bell. But presently a receiving device was perfected which ignored all sounds but those of the bell, thus giving the mariner a means of protection against accidents that could be depended upon absolutely at all times regardless of speed or weather conditions.

When this stage of perfection of the signaling device was reached the various governments began installing the instruments on buoys, lighthouse sites, and light-ships, using various mechanical devices for ringing the bells, and timing the strokes so that the mariners could tell by the intervals just what bell he was in touch with, as he knows each lighthouse by the intervals between the Hashes of its lights. A further development in the signaling device was to equip ships with submerged bells, as well as with the receiving apparatus. In this way two ships could communicate with each other, or with a shore receiving station, by using the Morse telegraph code, just as in the case of telegraphy.

The maximum distance at which such communications may be detected is about fifteen miles, and the approximate distance from the bell can be gauged from the clearness of the sound heard in the telephone receiver. At the distance of a quarter of a mile the sound of the bell is so loud that it is painful to the listener if the receiver is held against the ear, while at ten or twelve miles the sound is scarcely audible.

Probably the most dramatic rescue at sea in recent years was that of the passengers and crew of the steamer Republic, referred to a few pages back. When her wireless messages of distress were received a score of vessels went groping in the fog to her assistance, while the entire civilized world waited in breathless expectancy. Most of the rescuing vessels, although constantly in communication with the stricken ship, were unable to locate her. But the successful vessel finally got in touch with the Republic's submarine signaling apparatus, and aided by this located the vessel and rescued the crew and passengers.

This is only one instance of the practical application of the submarine signaling apparatus. But its use is not confined to the larger boats. The apparatus can be made so small that even boats the size of a fishing dory may be equipped at least with the sounding device, and thus protected.

On the Newfoundland fishing banks one of the chief causes of loss of life is the running down of the fishing boats in the fog by passing steamers, and also the loss of the dories of the fishermen who are unable to find their way back to their vessels. Many of these fishing vessels now supply each of the attending dories with a submarine bell which weighs about forty pounds and is run by clockwork. When caught in the fog the fisherman hangs this bell over the side of his dory and thus warns approaching steamers of his position, at the same time affording his own vessel a guide for finding him and picking him up. In this manner the appalling loss of life in the fogs on the fishing banks has been greatly lessened. Thus the submarine signaling device gives aid to the smaller craft as well as the larger vessels.

For the moment this is the last important safety device that has been invented to help lessen the perils of sea voyages. Indeed the perils and discomforts of ocean voyages are now largely reminiscent, thanks to the rapid succession of scientific discoveries and their practical application during the last half century. The size of modern vessels minimizes rolling and pitching. Turbine engines practically eliminate engine vibrations. The danger from fires was practically eliminated by the introduction of iron and steel as building material; the danger of sinking after collisions is now guarded against by the division of the ship's hull into water-tight compartments; sensitive instruments as used at present warn the mariner of the presence of ice-bergs; wireless telegraphy affords a means of calling aid in case of disabled machinery and giving the ship's location in a general way; while the submarine signal makes known the exact location of the stricken vessel in foggy weather.