Atlanta Georgian. [volume] (Atlanta, Ga.) 1912-1939, 1912-12-31
Travels on Heels of Light.

The lightning bolt travels on the
heels of the light, so that it, too, so
far outstrips the sound that if it
struck you, you would never hear
the thunder
Even we, however, are able to
send death dealing bolts faster
than the sound that accompanies
their discharge. A swift rife bull
let goes twice as fast as the crack
of the exploding cartridge.
Another useful fact to know is
that sound travels faster in water
than in air, in the proportion Of at
least four feet to one In some ex-
periments sound has been trans
mitted through the water of a river
at the rate of more than a mile per
second, but its average velocity in
water is about 400 feet per second.
The sound of a bell warning a ship
to keep away from a dangerous
shoal would require about % sec
onds to go five miles through the
air. while the same sound could be
transmitted through the water IN
about five and a half seconds
There are imaginable circumstances
in which the eighteen seconds thus
saved might suffice to prevent a
shipwreck
Still more remarkable is the dir
ference between the speed of sound
in air and in solid bodies. In the
heavier metals, such as lead or
gold, sound travels at nearly the
same velocity as in water. but in
more elastic metals, like iron and
steel, its speed suddenly increases
to more than three miles per sec
ond, which is six or seven times as
rapid as the flight OF a bullet
In wood sound travels about as
fast as in iron, provided that the
direction in which its waves move
is the same as that in which the
tibers of the wood run, but if the
sound is transmitted across the
grain of the wood it's speed is re-
duced to from a half to a quarter
Of what it is in the other direction
the amount of change varying for
different species of wood.
Waves of Sound Differ.
You can hear the sound Of
scratching on a wooden fence at an
astonishing distance, if your ear
happens to be close to the wood. or
if your head touches the fence. And
so quickly is the sound conducted
that, although its point of origin
may be quarter of a mile away
yet, if you are unaware Of the
manner in which it has been
brought to your ear, you may be
completely deceived. thinking that
it must have originated but few
rods off. one might easily make a
KIND OF telegraph of a wooden
fence, conveying messages by taps
upon it. This suggestion is dedi-
Gated to writer's of ingenious sto-
ries of adventure.
How long are the waves Of sound
in the air? They differ according
to the pitch
N+'' a - q sc lllAIG NOltt, III Olhh-
nary conversation. produces waves
varying in length from eight to
twelve feet while those Of a wom-
ans voice are only from two 10
four feet long. Waves sixty or
seventy feet in length, vibrating at
the rate of sixteen times per Sec
ond, produce a very grave sound
which is scarcely perceptible by the
human ear while waves only half
an inch IN length. vibrating be-
tween twenty and thirty thousand
times per second. produce e sound
SO shrin that it, too. passes beyond
tine range % our hearing, although
it may seem as hoarse as the roar
OF thunder to the hearing apparatus
of insects. All sounds whether
grave or shriu. travel forward al
tine same rate.