The Wichita daily eagle. [volume] (Wichita, Kan.) 1890-1906, 1898-01-11
News Of Recent Science
WHY THUNDER ROLLS.

through which it is transmitted, or per-
haps it is better to say that the velocity
is effected by the elasticity Of the me-
dunn, writes Elisha Gray. in the, Chicago
been made to determine the velocity of
sound when transmitted through different
media, and long tables on this subject
may be found. The following table will
give a general idea of the velocity OF
sound through solids, liquids and gases:
The velocity through air, LILO feet per
second.
times that of air.
The velocity through iron, seventeen
times that of air.
The velocity through pine wood, ten
times that of air.
Sound cannot be transmitted through a
vacuum, as the following familiar exper-
iment made by philosopher by the name
Of Hawksbee as far back as 100 will
show. Place a bell that is operated by a
clock work inside of the receiver of an
air pump. This receiver is a large bell
glass STOuHu 10 Ildhe du Gil lA5Al III 1A-
the bedplate of the air pump. Suspend
the bell inside the receiver by some kind
of cord that will not transmit sound, and
then set it to ringing. AT first it will
ring as loudly as though it were in the
open air. Now, work the pump and eX-
haust ethe air. The sound will grow
fainter until nearly a perfect vacuum IS
obtained, when the sound will cease, al
though the hammer is still striking the
bell the same as t.irst. Now let the air
in and the ringing is heard again.
Reasoning from the above experiment.
one should expect that sound would not
be as loud on high mountains as down
on the sea level. This is foun dto be
the case because the air at very hlgh
elevations is much lighter and less elas-
tic. For the same reason sound will be
carried farther and seem louder on some
days than others. When the barometer
is high it shows that the air is dense,
and dense air is a better medium for
sound transmission than rarified air. the
experiment with the bell in vacuum
shows that sound is transmitted only
through material of some kind that may
be made manifest to our senses. 1t also
shows that materials we understand it..
is not necessary for the transmission of
light and radiant heal, for both light and
radiant heat will pass through this vacu-
UNI, when the bell will not sound, as read
lily as through the air
Sound is reflected like light. 1t may
be focused on a single point, like light
or radiant heat, by means of concave, re-
Electors. 1t tends to move in straight
lines, but will in a degree so around an
object, but the object will cast dis
tinct sound shadow, if we may use the
term. If we throw an elastic ball on the
floor with considerable force it will re-
bound at the same angle at which it
was moving when it struck the floor. The
direction it was moving before it struck
Is called the angle of incidence, and
the direction it moves after that is called
the angle of reflection. Sound and light
obey this law. Sound waves are reflected
from polished surface the same as light
waves, and they obey the same laws in
the matter of focusing and dispersion
that light does.
A striking instance of sound reflection
may be noticed any time during the pas
sage of a thunderstorm. Whoever has
stood on a mountain top towering 1900
feet above the sea and from this view
point out a cloudless sky and bright sun
shine has looked down upon storm
cloud lowering far below against the side
Of the mountain, and stretching far
across the valley, has witnessed a scene
of grandeur that no language can ade-
quately describe. 1t is from a view like
this that one gets an accurate conception
of cloud form as it really is. Great bill
Lowry mountains whose crests are tipped
with purest silver and whose shapes are
as multiformed as the leaves of the for
est and as numberless as the sands of
the desert.
A storm cloud as seen from above, I'M
der the full rays of the sun, appears to
be and doubtless is. made up of a series
of clouds that may not touch each other.
During the progress of the storm one
or more of the clouds become surcharged
from time to time with electricity, when
it seeks to establish an equilibrium, by
discharging into the earth or into an
other clodu. This discharge causes a
great sound wave to flow out from the
point of disruption much louder than the
travels. as we have seen, at the rate
of LOO feet per second through the air in
all directions. Suppose some one is
standing one mile from the point of dis
ruption in the cloud. watching the opera
ton of natures power house. He sees
a fash of lightning. and in a little less
than five seconds he hears the thunder;
and, although there has been only a sim
gle report like the firing of a cannon,
it seems to the observer TO be a great
many following each other in rapid sue
cession. We have seen in former chap
ter that sound wave moves out like an
expanding globe from a common center,
which is the origin of the sound impulse.
\ part of the wave coming from the
cloud moves in a direct line toward the
observer. When the wave strikes his ear
there is a sensation of an explosion OF
great power, and this is followed by 9TH
ers in rapid succession. for esveral Sec
onds. each succeeding one growing weak
er until it dies out in what seems 70 be
a distinct roll of thoUnder. The explana-
ton is this: Beyond the cloud where
the discharge took place. and farther
away fromfthe observer, is another cloud
with a large rejecting surface. ard be-
yond that 4 second. q third. and so on
it may be. for many miles. Each one
OF these surfaces reflects back 70 the
ear Of the observer 4 part OF this great
sonorous impulse; but as part Of thC
wave that is reflected, is reflector from
the successive cloud surfaces that arc
farther away. and no two cf them rhf