THE MINE THAT HEARS.

Pukekohe & Waiuku Times, Volume 5, Issue 215, 6 October 1916, Page 1 (Supplement)

THE MINE THAT HEARS.

By EDWARD F. CHANDLER.

(In the present article, in "Popular Science Monthly," Mi*. Chanaler describes anothero ne of his remarkable applications of the microphone to naval weapons an application which is based 1 upon a ripe experience gained in the development of torpedoes and other inventions. The "Mine That Hears" is the result of sieverail years of constant study and experiment by the author, and is described in detail for the first time.) Eve/ybody knows that Jn time of ar harbours are protected l by mines, irough which an euemy cannot easily iss without the risk of destroying mself. Depending on their nature, le mines, iare called " qomtact" i r ihore-coutrolled." As the names mcate, the contact mine explodes as ion as a trigger with which it is prided is actuated by a ship, or a bottle : acid is spilled on a suitable chemiu; the shore-controlled mine is exloded electrically from a station at le critical moment determined by ob-

H-vation. Of the two kinds the shore-controlled the safer. The contact mine miy reak loose and become a menace to evitral shipping, as the tragic indents have abundantly shown. The British Grand Fleet undoubtedr owes its safety in part to the subtarine mine. It lies in harbours, the utrances off which are sewn with lines so thickly that a submarines mid not worm its way through them ithout blowing itself up. Whether 01 ot the feat of running through a line-field has actually 'been performed i the war, there is at least reason to elieve that it has 'been attempted, [r. Simon Lake, a leading authority n submarine boat construction n merica not only declares that a su')> larine can penetrate a mine-field, but as shown libw it can be done. Ha as devised a special typo of submarine rovided with an antennalike projeclon or "feeler" in front, which enables submarine commander to push aside lines with reasonable safety. If the Lake and similar systems are .ble to perform their functions it is bvious that no harbour is absolutely ai'e from submarines. In previous rticles published in the "Popular oience Monthly," I have shown how orpedocs can be automatically steered oward ships, which they are intended o destroy, by employing microphones o pick up the propeller vibrations, nd how submarine boats, which are otoriously blind under water, can be irected accurately toward a hostile eased by the same means. I hav? worked out a method of applying licrophones to mines, which, it seems o me, makes it quite impossible for a übmarine to enter a mine-sown hariOur; and which also enables the offier in command of aJ station from

rhieh, it seems to me, makes it quite mpossible for a submarine to enter a >ine-sown harbour, and which also enbles the officer in command of a stalon from which shore-controlled mines re fired to detect the attempt of a surace vessel to enter under the cloak of dense fog. The system which I have devised rould render it possible to blow up a übmatine trying to worm its way ino a mine protected' harbour, or a batleship seeking to enter a harbour at light or in a dense fog. In my sy.»em the mines are arranged in groups f four, .each group constituting a field init. On each mine a microphone is nounted. The microphone is an intrument for intensifying feeble sounds r for transmitting sounds, and: it i? >ased on the principle that the transiipn between loosely-jomed electricul pnductors decreases in proportion as hey are pressed together. The conluetors form part of a circuit through rhich a current is passing, and the -ariations in pressure due to sound caves in the vioinity of the conductors iroduce variations of resistance and luctuations of the current so that the

minds are reproduced' in a telephone eceiver. In the modern telephone tin xansmitter is essentially, a micro>hone, the pressure of the JNjpd waves >eing communicated to the nductor? >y means of a diaphragm. These microphones literaJly hear the 1 urn of a submarine's motor. Not only hat, but tl'.e particular microphone vhich hears the submarine best, f>eiause it js nearest to it, can be easily ocated. It is sample enough to Jeerm'.ne whether a submarine is nearer nine 1 or mine 2 of a given field uni& if four mines.

The field units are interconnected ilectrically. so that the entire harbour s sown not only with charges of high 'xplosive but with microphone detectirs. Interconnecton is necessary beause mines 1 and 2 of one group con.titute mines 3 and i of an adjacent 'roup. Miorphones are so remarkably ensitive (they have picked up the hum >f submarines fifteen miles away in the )resent war) that they need not be ijyishly employed in every wise. Four nyrophones placed in the four corutj of a small field would answer ; n liany cases, all the more so since a ihip tsui be blo-.vn up even though it !>e ifty feet from the actual exploson. !'W of us realise how terrific is the disruptive efiect of the gases suddenly generated when several hundred lounds of explosive are detonated. A mine-field equipped with micro)hones in the manner indicated is elee-,rical-ly connected with a luminous anlwnciator. In other words, wires run : rom each microphone to a board whi h s divided into squares corresponding in number with those of the mine-field linits. Asa hostile ship passes through H mine-field the nearest microphone* pick up vihrnt : ons of her propellers and Corresponding lamps on a board {flow. Th? luminous annunciator may Tic twenty or more miles distant from the microphones: it may be in Chicago and Hie minefield in New York Harbour It is alwjivs possible to follow te cov- • if an intruding vessel merely bv mf h ing the I'ghts as they flar<- up ami >7; nit in the squares of the lua.iiiotx "■ mineiator. The In nips actually • isp the '-ourse Hk-n by the \uulor e!><" i v '"II. !•' she enter : '|'rn>' 22 of ♦ > ''•! the limn I«*hind >-«|iistr-» >•> i■ :ne'iii-!.itor heird i-h-w.: « • Ii" . . ■ I , uuare 2:t of il«. >.iir.cI'elH ■ i «'\-tingui .• ."'1 lamp Mines • ■ r-en-i'v To provide i them u"f.! n::< r<;i>hon'. and ■> «iro the mierfNph"pf« to luminous :.nnniv''>ter I board adds to the font of the instCl'a-

tion. Suppose that it were possible to use fewer mines in other words, to use rather large squares —and suppose it were possible to determine not merely the particular square into which :: hostile vessel has found its way but the particular mine of tha't square nearest which it happens to be —would not that solve the problem of cheapening the installation and' heightening its etfectiveness ? With this idea in mind,l have connected with the luminous annunciator board what may be called a " precision indicator," the purpose of which is to show which mine is to be exploded m order to destroy the interloper. A siugle precision indicator serves for ail tiie mines; for the wiring is such that the precision indicator can be switched into the circuit of any mine-square at will. The details cannot be revealed at the present time, because they are the subject of a patent applioatiri awaiting official action. It may be stated, however, that the devices employed accurately locate a vessel in a square by averaging the momentaryresponsiveness of the four microphones at the corners of the square. - Imagine New York mined and microphoned in the manner that I have described; imagine tho mines connected with a luminous annunciator at Fort Wadsworth and with a precision ind'cator provided for the purpose of determining which microphone in a square hears the most; imag'ne a submarine crawling very, very cautiously through the field, thrusting aside with careful antenna the anchor-chains if the buoyant mines in its path. An American officer glues his eyes on the luminous board. One by one the squares glow before him—l 9, 36, 53. 66. Unwittingly the submarine's commander plots his course in a trail of light. He cannot be seen with human eyes; and yet he is as visible, electrically at least, as a goldfish in a bowl "Square 78," says the American officer to lidmself, as a new light flashes up. The time has come for decisive action. He pulls a handle arid switches the •precision indicator into electrical connection with square 43. The submarine is nearest mine "A" of that unit, for the microphone on mine "A" is intensely active. He presses i button. Miles away a column of water is tossed into the a ; r, and an unsee-i enemy has been destroyed' with awful suddenness. v The naval and military strategist will note at once that the system which I have described has this advantage over the rather haphazard method of utilising the contact mines at present employed. It renders it possible to destroy a whole fleet, shb by ship, as it progresses .into a harbour which is protected.