ECHOES OF WAR

New Zealand Listener, Volume 3, Issue 57, 26 July 1940, Page 14

ECHOES OF WAR

(Wrtten for "The Listener" by

Ronald

McIntosh

HILE the Blitzkrieg was raging at its fiercest in France and Flanders, it was possible at times for the noise of the gunfire to be heard in England. At one spot in particular, at Fritton, near Great Yarmouth, crowds gathered every day around the shores of a small lake to listen to the war. The lake. was surrounded by trees, and these acted in conjunction with the flat surface of the water to gather and amplify the faint echoes and make them audible. Such instances of abnormal hearing are not rare. It is recorded that Sir Isaac Newton, the great mathematician and astronomer, standing in the gateway of Trinity House, Cambridge, heard the guns of a naval action between the Dutch and the English, although at Deal and Dover, much nearer the engagement, no noise was audible. Newton foretold a British victory from the fact that the noise gradually became fainter, indicating that the victors were driving the Dutch away from the coast of Eng-

land. Pepys also records a similar phenomenon in his famous diary. This is What Happens Until very recent years, however, it was not known that such noises are really echoes, coming to their hearers from high in the atmosphere. It would be impossible for a noise, however loud, travelling close to the earth’s surface, to cover more than fifty or sixty miles, What actually happens is that portion of the sound waves travel up into the atmosphere. Passing through successively colder regions they reach, at an altitude of about thirty miles, a warm layer of ozone, formed from the bombardment of the atmosphere by ultra-violet radiation from the sun, and this layer is at a temperature similar to that on the surface of our globe. This warm layer of ozone turns the sound waves back toward the earth once again, and they finally become audible on the surface 100 miles or so from the source of the noise. Explosions on a greater scale than gunfire, such as the eruptions of Tarawera and Krakatoa, have revealed that this reflection of echoes can be repeated more than once,

producing areas of audibility separated by zones of silence up to three thousand miles from the erupting volcano, Long-distance Radio The phenomenon of sound reflection is nature’s illustration of long-distance radio reception. Electromagnetic waves, like those of light, travel in straight lines, and it would be impossible to hear a radio station at any distance beyond the area covered by its ground wave if it were not for various ionised

layers in the atmosphere, the lowest of which is situated at about twice the height of the ozone layer which reflects normal sound waves, and the highest at an altitude of about 120 miles, These ionised layers catch the radio signals and treat them as the ozone layer does sound waves, bending them earthwards repeatedly in all sorts of curious reflections between the various layers and carrying them for great distances, so that we are able to listen to Daventry, on the other side of the globe,