Evening Republican, Volume 21, Number 236, Rensselaer, Jasper County, 20 October 1917 — JUST WHAT CREATES ECHO [ARTICLE]

JUST WHAT CREATES ECHO

Under Proper Conditions Any Kind of a Sound Wave Will Be Effectively Reproduced. An echo is caused when the waves of air which you create when you shout are thrown back again when they are stopped by something they encounter and are turned back without changing their shape. Any kind of a sound wave will make an echo In this way. You see, you can have no sound of any kind without sound waves. You could not make a sound if there were no air. Now, when you shout, you start a series of sound waves that go out from you In every direction and they spread away from you in circles just like the rings, or ripple that are caused when you drop a stone Into a pool of water. You can prove this to yourself easily by having one, twh, three or more, of your friends stand around you in a large circle. You can' place them as far away from you as your shout can be heard If you wish. Whenvoushout. each of your friends will bour the shout at the same time, provided, of course, they are at equal distance from you. Sometimes these sound waves as they go away from you in circles strike objects that turn the Wavqs back unbroken just as they came to them. The Weaves will bounce back just like a rubber ball from a wall against which it

has been thrown and this is the echo. However, some things- that the sound waves strike break up these waves entirely and others partially. No doubt :you have sometimes noticed when you shout you bear a distinct echo and that at other times, standing j in the same place, 'you cannot hear any echo, although you shout in the same way. This is explained the air are such that no echo is produced while at other times a perfect echo results. —Book of Wonders.