The Iowa plain dealer. [volume] (New Oregon, Howard County, Iowa) 1867-1895, 1889-12-26
SOUND.


over the world and travels faster than
lightning express trains could carry any
OF us. Sound doesn't travel as fast %
| light though, for light could go 43C
times around the earth while sound was
| going its thirteen miles, for sound trav'
els thirteen miles . minute. However
We have nothing to do with light to-day,
and had better begin to find out how
sound is produced. You have often
stood on the shore Of lake or pond and
thrown in . stone, just to see the little
circles Of waves it produced, haven't
you? Now when you strike some hard,
elastic substance, like iron. copper, bell.
metal or glass, you set in motion waves
Of air just as you produced the waves in
the water, only you can not see them.
When these waves strike against the
drum Of the ear it produces : sensation
which We call sound. But you say some.
times we can't hear sounds distinctly,
well it is because something interferes
to break the little sound wave before il
reaches your ear, just as though your
little wavelet in the lake broke upon a
rock before it reached the shore. There
are many and different ways in which
the sound. waves are broken, sometimes
the falling rain breaks them up, and the
snow falling will stop their progress.
Then the sun in the daytime, heats the
air and produces strong currents and
breezes, SO that the air is not always
uniform. For this last reason we hear
sounds more distinctly at night, when
the whirl of business ceases and leaves
the air still. When air becomes rare
fed THAT means thin, not densel sound
becomes less intense, fainter. We know
this to be fact because IL you ring a
bell in the receiver of an air-pump and
then begin to exhaust the air, the sound
will keep growing fainter until the air
is all exhausted. That is the reason,
children, that mountains are so silent
and quiet, because the air Of mountains
is very rare or thin, and as the air be-
comes rarefied, sound diminishes.
1t is in this way that God has wrapped
: great silent mantle around His noun
tains, setting them apart from the noise
and hustle Of the world, and justhere
let me leave . thought with you. Have
you noticed how often Christ went apart
from the others on the mountains to
pray. and how he chose mountain for
His temple when He preached that won
derfnl sermon of the beatitudes? But
now we come to another phase of sound
waves strikes against an obstacle, like
. hill or wall, it Is thrown back or re-
Elected, just as when light is thrown
against bright surface it IL reflected
or thrown back. When this happens
with sound It Is called an echo. Tho
most famous places for echos are grot-
toes, old Abbeys, caverns and cathedral
aisles, because the sound-wave can not
pass beyond the walls and must be
thrown back. Sometimes these return
ing sound-waves become entangled in
turnings and windings Of the cavern,
and come back very deliberately. The
farther OF the echoing body is the more
sound Is reflected. Sometimes IN echo
will repeat two syllables, because the
echoing body 10 20 far on that there IL
time for one reflection to pass before an
other reaches you. Then, sometimes It
happens that there are two or more
separate surfaces that the sound-wave
strikes and reflects in succession. II
you ever 60 TO Scotland, children, ask
your courier to take you to place call
ed Rosmeath, seventeen miles above
Glasgow, for there is very remarkable
echo there. IF a trumpet plays tune
and stops. the echo will begin the same
tune and repeat it accurately; as soon as
this echo has ceased another will echo
the same tune in . lower tone, after the
second echo has ceased third will sue
coed with equal fidelity though in .
lower tone.''
At ono place on the lakes of Killarney
in Ireland, If the guide takes up his
pipe and plays any simple tune, the echo
will accompany him with an excellent
second. Christian at Work.