A good ear cannot distinguish one sound from another unless there is an
interval of one-ninth of a second between the arrival of the two sounds.
Sounds must, therefore, succeed each other at an interval of one-ninth
of a second in order to be heard distinctly. Now, the velocity of sound
being eleven hundred and twenty feet a second, in one-ninth of a second
the sound would travel one hundred and twenty-four feet. Repeated echoes
happen when two obstacles are placed opposite to one another, as
parallel walls, for example, which reflect the sound successively.
[Illustration: Fig. 108.—MISS ECHO.]
A certain river has a bend in it, avoided by every one, as it was
supposed to be haunted. At a certain hour in the evening, for many
years, terrible curses were distinctly heard. Suddenly they ceased.
Hearing an account of the strange phenomena, Mr. H. Panky determined to
ascertain the cause, and carefully examined the river on each side for
about a mile above and below the bend. He ascertained that at about the
time the sounds ceased an old fisherman, who had lived on the opposite
side of the river, full a mile from the spot where the curses where
heard, had died. He was told that the fisherman was in the habit of
crossing the river to a village, where he found a market for his fish,
and where he spent his money for liquor; and that after drinking freely
on his way home, while rowing across the river at night, he would swear
terribly. This gentleman then persuaded a friend to go down the river to
the place where the curses were formerly heard, while he remained in a
boat on the river at the point at which the old man usually crossed. He
then played on a bugle and sang several songs. His friend soon returned,
and with eager delight exclaimed, “O, Hanky, such glorious music fills
the air, just where the oaths used to be heard!” The neighbours came
rushing down to hear it, and some fell on their knees, praying. They
said, “The angels have driven the devil away.” Mr. Panky then asked what
were the songs they heard. His friend described them correctly, and said
he understood even the words, one of them being the famous Marseillaise,
another a German song. The foreign words made the ignorant more sure
that the sounds were supernatural. The magician then played on the
bugle, and sang again the same songs, while his friend stood by; but his
friend said the music was not equal to that he had heard below, where
the sounds had really seemed heavenly.
The peculiar configuration of the river-banks had concentrated the
sounds, and the distance and the water had softened them.