Because there are various reflecting surfaces, at different distances, each of which returns an echo.
"And God said, Let the waters under the heaven be gathered together onto one place, and let the dry land appear: and it was so."—Gen. i.
746. Are sounds reflected only by distant objects?
Sounds are doubtless reflected by walls and ceilings around us. But we do not perceive the echoes, because they are so near that they occur at the same moment with the sound. In lofty buildings, however, there is frequently a double sound, making the utterance of a speaker indistinct. This arises from the echo following very closely upon the sound.
747. Why, when we are walking under an arch-way or a tunnel, do our voices appear louder?
Because the sounds of our voices are immediately reflected. And as a gas reflector increases the intensity of light, so a sound reflector will increase the apparent strength of our voices.
There are many places where remarkable echoes occur. On the banks of the Rhine, at Lurley, if the weather be favourable, the report of a rifle, or the sound of a trumpet, will be repeated at different periods, and with various degrees of strength, from crag to crag, on opposite sides of the river alternately. A similar effect is heard in the neighbourhood of some of the Lochs in Scotland. There is a place at Woodstock, in Gloucestershire, which is said to echo a sound fifty times. Near Rosneath, a few miles from Glasgow, there is a spot where, if a person plays a bar of music upon a bugle, the notes will be repeated by an echo, but a third lower; after a short pause, another echo is heard, again in a lower tone; then follows another pause, and a third repetition follows in a still lower key. The effect is very enchanting. The whispering galleries of St. Paul's, of the cathedral church of Gloucester, and of the Observatory of Paris, owe their curious effects to those laws of the reflection of sound, by which echoes are produced; but in these cases the effect is assisted by the elliptical form of the edifice, each person being in the focus of an ellipse.