LISTENING FOR ZEPPELINS

Dominion, Volume 9, Issue 2777, 23 May 1916, Page 6

LISTENING FOR ZEPPELINS

At pre-determined points to the north if Pans are stationed groups of "cars," comprised of sensitive microphones, for :he purpose of detecting hostile aircraft states a writer in the World's Work."'ln appearance they resemble largo megaphones, and are not only capable of being turned to any point of the compass, but then; angle of adjustment through the vertical arc is Sfldeg.- They are linked Up by telephone, and the air-distance between each post is a known factor. The observer, receiver to'ear, listens intently, n ™ "f sw ' n snig the instrument round is ablo to catch the faintest sound of the Vhirrin<* of a propeller, as well as the beat of the engine. Once tho sound is Muse the ' ears" are moved both through th© vertical and the horizontal planes. If the sound ,increases the movement of the ear.is slowly,continued.in that direction until the peculiar hum reaches its'maximum. Kenntinie. tho observer consults the adjacent posts to Ascertain if they have picked up the noise, and, if so, the direction in -which they are-movin°- their respective ears. This brief consultation, which is speedily completed, i&.ces the position of the hostile aircraft, which must lie at the apex of tho pyramid or cone described by draiwing imaginary lines from .the posts upwards through the air to the point whence the instruments give ns being t!;at from which it is issuing.. The advantage of these ears is that "an nirahip or aeroplane may be picked up during its travel eithvir by day or night. After a short period of : training the observer becomes uncannily proficient in isolating the sound whiteh he desires and from a medley of foreign noises.