LISTENING FOR THE SUBMARINE

Dominion, Volume 9, Issue 2693, 12 February 1916, Page 13

LISTENING FOR THE SUBMARINE

THE "WHINE" IN THE SEA AN ENGINEER'S INVENTION A _ submarine cannot move under water without electric motors. Such motors give out a characteristic hum or "whine," as every visitor to a powerhouse knows. The recent invention of an American electrical engineer enables this sound to be heard twenty miles away, so that no German submarine can noiy enter a French or English harbour undetected. This engineer, William Dubilier, who went to Europe at tho invitation of tho Allies to devise a system of harbour defence against submarines, describes in "Popular. Science Monthly and the World's Advance" the steps that led to tho invention of his microphonic submarine-detector. He says:— "Suppose that a submarine gave forth a sound of some kind, would it not be povssible to dovise some form of apparatus by which it could be heard That was the starting idea of the experiments that I conduotcd for the Allied Government. It is not a new idea. Professor Tissot was hard at work with tho original experiments and had already used microphones for this purpose. Professor Fessendcn had made somo brilliantly successful experiments with an apparatus cf his invention, known as an 'oscillator, 1 which showed how easy it is to locate a steamship in a 'fog or at night, provided that it sent forth sound-waves. Tests of his instrument had also been made on submarines. But these investigations were all conducted with a device •which'was installed for tho deliberate purpose of making a rhythmic noise to bo detected. What was needed was some form of apparatus which would pick up the sounds sent forth by a submarine,, not deliberately, but involuntarily. 'At once the beating of tho propellers of a 'Submarine suggests itself. It is not characteristic enough. Motorboats, steamships, and other . powerdriven vessels have 'propellers, and although their period of vibration is different from that or any other enginedriven craft, some other sound must bo sought—something as distinctive as tho call of a robm or the neighing of a horse, something that by no possible chance can be mistaken for another sound. I found what I sought in tho weird, shrill hum of a submarine. Others had hoard that hum long before I began my experiments. It was taken for en-gine-yibratiou. But it is much too high ill pitch for that, as I found by actual tests. I soon convinced myself that the fine, shrill, almost singing note that can be heard when tho Diesel engines are cut off and the submarine is travelling under power derived from her storage batteries is due entirely to her electric motors. The microphone at onco suggested itself as a suitable instrument. - ■ . First Experiments. "In my first attempts to detect submarines by their cliaracteric hum, the microphone was sealed within a watertight container, and the whole placed in the water; The apparatus was a failure. It could not withstand the pressure of water oven at five fathoms. The container was Brushed like putty in a strong hand. In order that the diaphragm might successfully resist the external pressure, ait' was forced into the container until its pressure equalled that of the water. The new form of apparatus was much more successful than that first used. Submarines could be heard beneath the viatei at a disfcanco of five miles, and the apparatus stood up well, oven at gieat depths. But it had the great defect of bearing too much. Not only was the hum of a submarine picked up with astonishing clearness, but other : strange sounds of tho sea as well—the vibration of engines in passing steamers, tho beating of propellers in water. A steamer sets tho water vibrating with an intensity, thousands of times greater' than that of. a humming submarine. In that deluge of sound the submarine could t not ho easily detected. .. . Clearly, some kind of sound sieve was wanted—something that would sift out everything but the singing submarine." Out of the Babel: Tho.Whine. Such a "sieve'' was found in a resonator, like a tiny organ-pipe, tuned to the exact pitch of the submarine's electric hum. It picks out just the sound that is sought, amid a babel of others; and tho microphone, which is built on the plan of a telephone-trans-mitter, then magnifies it so that the ear can hear it. In this way a submarine can be hea/d under water, twenty miles away. A modification enables the position of the U-boat to be detected with somo accuracy. Says Mr. Dubilier: "This microphone, or electrical eat, as it may well bo called, proved to bo extraordinarily sensitive. . . . An<j it behaved curiously like a telephone. Talk squarely into a telephone-trans-mitter and the man at the receiver will hear you clearly; talk into the transmitter sidowise, and you will be heard less distinctly. So it proved with the microphone: When the singing , note sent out by a submarine under water struck the microphone squarely it was heard much more distinctly than if the microphone were inclined to tho soundwaves. That_ made it easy to tote in which direction the submarine was travelling. The microphone had merely to be turned until the hum was heard most distinctly.