The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1904-02-26
NOISE MADE BY METEORS.
Various Theories to Recount for ths
Rumble That Is Sometimes
Heard.

The great majority of meteors are
silent. They glide through the air with
out encountering much resistance, be-
cause the bits of stone of which they are
composed are usually very small-not
bigger than pebbles, perhaps. They fly
with such velocity, though, that friction
with the air makes their surface incan-
descent, and they are visible at a con-
siderable height, even if noiseless. At
rare intervals, however, the atmosphere
is penetrated by what are probably lar
ger masses of stone or metal. Owing TO
the fact that tie exterior expands from
heat more rapidly than the interior,
which retains the inconceivably low tenn
perature of outer space for several sec
onds, or from some other cause, these
''freballs" are attended by sound. This
has been described as resembling the
noise produced by moving heavy piece
of furniture over a bare floor, or distant
thunder, or a prolonged volley of mus
kerry
The meteor moves so rapidly that
there is. as it were straight line many
miles long and 100 miles distant from the
observer which becomes the source Of
sound waves starting almost simultane-
ously from the whole length of the path.
According to the United States Weather
Review, the concentration of these
waves at the observers station explains
the explosive noise and the subsequent
rafting, but what makes the original
violent sound waves? There are four
ideas as to this, all of which may De
true:
First-The meteor strikes the air so
violently as to produce the same effect
as when il strikes liquid orssolid.
Second-The rapid movement Of the
meteor leaves a long vacuous trail, into
which the surrounding air rushes and
the impact of air on air starts the sound
wave
Third-The meteor revolving rapidly
On its axis, striking the air myriad of
times on all sides, produces rapid sue
cession of waves.
Fourth-The meteor is so heated by
the compression of air in front that 1t
burns and cracks, and there is a contin-
uous suffering as its surface particles
burn up, split off and flow away.
What are the phenomena of sound OBJ
served a short distance from the path OF
a projectile when going past the observer
at the greatest possible speed? This
question the editor of the Review pro-
pounded to a number of naval officers
One of them replied: While in the Office
at the naval proving ground | have, Of
course, frequently heard the sound Of
passing projectiles. AS the disturbed
air wave reaches you, sound is made
that is about half way between boom
and crack, and then moment later
comes the boom of the discharge. The
crack is almost as loud as the boom,
and perhaps a little more annoying.
When large shot tumbles, the rumble
sounds to those near the trajectory like
that of a railroad train
Probably no shot from a cannon
travel faster than $500 or 1900 feet a
second This is from half to two-thirds
of mile. Many meteOrs move at the
rate of ten, Is and even 20 miles second.
Besides, their irregular shape ought 10
make more of a disturbance than a
smooth and symmetrical shot from a
cannon. The editor of the Review does
not himself choose between the four
theories that have been advanced, but
one Of the military officers who was per-
haps thinking of the commonly accepted
notion Of thunder, lays much stress on
the thrush of air into the vacuum created
by the passage of the meteor