The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1920-05-20
VALUE Of GEOPHONE
IN MINING OPERATIONS
DESCRIPTION OF INSTRUMENT
OF GREAT SERVICE IN
MINE DISASTERS.

vented by the French during the war
to detect. through the earth, the
sapping and underground mining OPP
erations of the enemy 1t was inn
proved by United States engineers,
and more recently has been further
improved by the engineers of the
United States bureau Of mines, and
its use in connection with special
sounds has been developed.
The instrument. though small is
essentially a seismOgraph, since it
works on the same principle as the
ponderous apparatus by which earth
quake tremors are recorded. II con-
sists of an iron ring about three and
one-h half inches in diameter within
the center of which is suspended
lead weight that is fastened by a sin
gle bolt through two metal discs
(pure nickel discs OOPS inch thick are
usedl one of which covers the top
and the other the bottom of the ring
There are two brass cap pieces, the
top one having an opening i'm the CEN
ter to which is fastened a rubber tube
leading to stethescopic ear piece.
These cap pieces are fastened with
bolts to the iron ring and serve also
to hold the metal discs in place.
How 1t Operates.
We then have really nothing but a
lead weight suspended between o
thin discs that extend across small
air tight box If the instrument is
placed on the ground and anyone is
pounding or digging i'm the vicinity
energy is transmitted in wave mo-
ton through the earth, and the earth
waves shake the geophone case. The
lead weight on account of its mass.
and because it is suspended between
the discs, remains comparatively mo-
tionless. There is thus produced a
relative motion between the instru
ment case and the lead weight The
result is that in the thin space over
the discs a compression and .rarfica-
ton of the air alternately takes place
which is magnifed at the small out
let Since the rubber tube leading TO
the stethescopic ear piece is con
nected with this space i'm the geo
phone the vibrations are transmitted
TO the ear drum and like other rapid
air waves produce sound effects. Usu-
ally two instruments are used one for
each ear.
When two Instruments are used. IL
has been found that the sound is APP
parently louder from the instrument
nearer the source of sound, even
though the geophones are placed not
more than two feet apart Ii is evil
don't fbaf IN ,,,ox-fpe. tl,., fpuf,,ttpapfc
a point can be found where the sound
will he of the same apparent intensity
in both ears The direction of the
point of origin of the sound is then
on perpendicular to the line con
Meeting the centers of the two instru-
ments. either in front of or behind
the observer Further observation
will SOW which side Direction Is
quite accurately determined in this
way. The sound is not actually loud
err in one ear than in the other. but
the ear is capable of distinguishing
the slight differences in time at which |
the sounds arrive in the two instru- /
ments. Since this is the case persons /.
who are slightly deaf in one ear are /
able to determine direction with the /
instruments.
How instrument Is Utilized.
The bureau of mines has conducted /
an investigation to determine the I
conditions of operation under which /
the geophone will give the most sat
isfactory results when used for rescue /
and survey work in both metal and
coal mines.
In coal mines il has been determin- I.
ed that the geophones should rest on .
solid shelf of coal or on the floor OF
a niche cut into the coal The floor /
of the mine is likely to be covered .
with dirt and is very seldom solid .
enough to transmit sound well. In .
metal mines the geophones will of /
course. be held against or placed up-
on the natural rock. If the geophones .
are held with the hands against the .
coal vibrations are set up by the cir .
culation of the blood within the hands .
that greatly interfere with successful /
observations on the other hand the .
rock appears to withstand these vi .
brations and successful results can .
be obtained by simply holding the in
StrumentS IN pace upon lnt iN'h-
How to Signal.
If man is pounding in the hope
that he may be located by means of
the geophones. he should strike heavy
slow blows upon the coal or rock. The .
best results are obtained with
sledge or heavy stick of timber This
is true even if the man expects TO be
located by a party operating upon the
surface. There is no advantage i'm L
pounding upon the mine roof. The
sound transmission is not so good
and the process is more fatiguing II
is of course, known that sounds are
transmitted very well along rails and
pipe lines The investigation has
shown that while sounds may be
transmitted great distances if the
rails are laid upon ties or the pipes
are suspended. on the other hand if
fbax- arc hurled in loose dirt for a dis