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The Mystery of the Echo

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The Mystery of the Echo ttte science of acoustics is, as yet, in its .nfanepf and men have much to learn before they can solve the mystery of the echo or predict her fleeting Moods, writes Miss Gertrude Bacon in Good Words Belated in general terms the explanation of echoes j$9 simple and easy to understand. Sound, as we know, is conveyed to us by vibrations of the air, Which spread around from the source of sound uaotly as waves of "iter spread in ever widening «ngs when a pebble is thrown into a still lake. ery frequently it happens that these waves ol aoond, in their outward course, strike against soma Surface of such a nature that they are, by it, 00seted back again without being broken and flattered. And when it occurs that these www On returnea at "uch an angle as to strike the ear •ff a listener, we have what we call,an echo. Often tMte than one reflection goes to tobtl making up ot On echo, the sound-waves being thrown from OM omgbft to another in their* passage to the ear-just so a billiard ball will rebound from cushion V •ashloa on its way round the table. This, ronghlj fti the car.se of the phenomenon. But so ending MM the variations of circumstances and environ- Bent, and the effects they produce so far-reaching tttd hard to foresee, that we are continually being token anawares. Sometimes tile echo returns M ■sickly that it eannot be distinguished fross tiw Irtgtnal sound; and yet its undetected pre*- nee is enough to affect seriously the penetratioa tf a roice in a church or theatre Sometimes 8M sound will produce several echoes in differeat directions, which return and return again at different time intervals, to the great distraction wt the hewers. Again the surface of the releethtf has a great deal to do with the nature « the echo returned. Certain substances seess to have a tendency to absorb the sound-waves, aad Silisn to efiect them more readily. Another curious property of sound-waves, exemplified in many waiU gse»a buildings, is the tendency 1 4 the waves te no round a eurvsd apse or gallerr, much as a Wars ol the sea, striking aslant oa a shallow bay, ■III ran round the shave. This is tha exniaaaitap ghjggy familiar aroostis caxioeitia^ notafefy