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The Myatery of the Echo

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The Myatery of the Echo The science of acoustics is, as yet, in its tifaney, and men nave much to learn before they can solve the mystery of the echo or predict her fleeting Moods, writes Miss Gertrude Bacor in Gcod Wordt- Belated in general terms the explanation of echoes w simple and e&sy to understand. Sound, as we know, is conveyed to us by vibrations of the ahr4 Which spread around from the source of sound aotactly as waves of Titer spread in ever widening tings when a pebble Is thrown into a still lake. Very frequently it happens that these waves of IØUnd, in their outward course, strike against soese anrface of such a nature that they are, by it, feflected baclk again without being broken and Scattered. And when it occurs that these waTef IMM returned at duch an angle as to strike the ear Of a listener, we have what we call.an echo. Often more than one reflection goes to thfl making up. of to echo, the sound-waves being thrown from oss andam to another in their passage to the ear-juef as a billiard ball will rebound from cushion to Cushion on its way round the table. This, rough)# Is the cai^se of the phenomenon. But so endleit are the variations of circumstances ,nd environ* llent, and the effects they produce so far-reaching and hard to fere see, that we are continually being taken unawares. Sometimes t;be echo returns St faickly that it cannot be distinguished frosa tilt gnginal sound; and yet its undetected pres* Mice is enough to affect seriously the penetratioa if a roice in a church or theatre Sometimes ene aound will produce several eohoes in different directions, which return and return again at different time intervals, to the great distraction at libe hearers. Again the surfaoe of the reflecting abject has a great deal to do with the nature el the echo returned. Certain substances seem to have a teniencv to absorb the sound-waves, and ethers to eflect them more readily. Another curious property of sound-waves, exemplified in many well- known buildings, is the tendency « 4 the wares to run round a eurred apse or gallesr* much M < Ware at the sea, striking aslant on a shallow bay, Will ran round the shore. This is the explanation familiar acoustic curiosities, noiftbgf HI Whitgern^ a alloc? «f gt,