The Prince George's enquirer and southern Maryland advertiser., 1922-08-25
instrument Developed During
World War Has Been Per-
fected by Engineers.
EXPERIMENTS PROVE VALUE
Detects Subterranean Sounds at Great
Distance-Has Many Uses, but Its
Advantage in Mine Rescue
Work Most Important.

Washington.-As the result of ex-
periments made by the bureau of
mines, the geophone, novel instru-
ment used amid the reek and slaugh-
ter Of the World war for the detection
Of earth and rock sounds, made In
the construction of military mines and
tunnels, promises to become an active
factor in the saving of the lives OF
miners entombed as the result OF hres
and explosions.
In the course of tests conducted IN
the bureaus experimental coal mine
near Pittsburgh, blows with a sledge
on the coal face were heard, by means
of the geophone, at distance OF 6oo
feet, with various rooms and entries
intervening. On a suspended pipe
line, light hammering with the knuck-
les was detected at a distance OF
1,500 feet. Ordinary talking and sing
ing could be detected through $50 feet
Of solid coal. By the use of two geo.
phones, one instrument to each ear
1T is possible to determine the dlrec-
tion from which a sound is coming,
and thus to locate the approximate
position of the entombed miner.
Another promising use of the geo.
phone is in the location of leaks IN
water pipes. By means of the instru-
ment, it is possible to hear water cir
culating in the pipes of ordinary city
mains situated ten to fifteen feet below
the surface. Tests conducted at a
busy corner in the downtown district
of Pittsburgh located leak in water
main which the water company had
sought to detect for two weeks vainly.
Sensitive, but Simple.
The mine geophone is sensitive, yet
extremely simple and easily portable.
The instrument was invented by the
French during the war to detect sap
ping and underground mining opera
tions. 1t was developed by the United
States engineers, and the instruments
now used by the bureau of mines were
made according to plans drawn by
them. except for the Introduction of
different diaphragms. The geophone
is essentially a small seismograph, as
1t embodies the same principles as the
ponderous apparatus that records
earthquake tremors. 1t really consists
of a lead weight suspended between
two elastic diaphragms cutting across
a small alright box. If the instru-
n.cnt is placed on the ground and any
one is pounding or digging in the
vicinity, energy is transmitted as
wave motion to the earth, and the
earth waves shake the geophone case.
The geophone, therefore, transforms
the earth wave into an air wave,
which is heard by the ear as sound,
and at the same time magnifies the
wave so that the sound is louder than
If the ears were placed in direct con-
tact with the earth.
The observations Of the bureau of
mines indicate that the geophone
should be quite useful in the loca-
ton of mine fires. Usually mine
fire makes enough noise, either by
drawing air or by breaking off slate
and coal, to be heard for a consid-
erabIe distance through the coal, and
even through the strata above. The
distance that these sounds can be
heard depends great deal on the ma
ture of the strata above the mine, yet
the sounds originating at mine fire
should be detected through 100 to 300
feet of cover and through 500 to 800
feet of coal.
Aids Mine Engineering.
Geophones supply quick and fair.
ly accurate method of mine surveying.
If two tunnels are being brought to-
gether from any direction, the
progress of the tunnels could be OBJ