Echo

Repetition of any sound caused by its reflection from some obstacle. A certain least distance from the source of sound to the reflecting surface is obviously nece ary for the production of an echo. For the repetition of a monosyllable about 42 meters is required, and with this as a basis the distance is proportional to the number of syllables or distinct sounds succe ively produced. Reflecting surfaces in some cases have been so arranged, either by nature or artificially, that the original sound is repeated many times, thus producing multiple echoes.