Atlanta semi-weekly journal. (Atlanta, Ga.) 1898-1920, 1919-04-22
THE GEOPHONE-By Frederick J. Haskin

investigation of the factors influencing the
transfer of energy from. a mining tool to the
clay and coal was also made in order that
recommendations could be made as to the
type Of mining machine which could be used
to accomplish the most work with the least
noise.
In this connection il was found that sounds
were transmitted only about half as far in
clay as in shale strata and about one-quarter
as far in clay as in coal. To give some idea
Of the SensitiVeneSs of the instrument it may
be said that pounding with a pick on the
bituminouS coal can be detected for a dis
lance of nine hundred feet, and the direction
determined, and that pounding with a sledge
can be heard far as eleven hundred and
fifty feet. These measurements were made in
the Pittsburgh coal seam in the vicinity of
Pittsburgh where the coal is somewhat hard
er than in most other bituminous coal beds
The explosion of one-ounce charge of dyna-
mite was detected a distance of over two
thousand feet through the shale strata.
One interesting feature of the instruments
is that the sound as transmitted to the ear
is very characteristic Of the instrument pro-
ducing the sound. To illustrate: Twelve
mining and carpentering operations were car
ried out on the coal rib. An engineer of the
bureau who had never used the geophone and
who did not know what tools were to be OPP
Grated, was able to recognize and name nine
of the instruments at a distance of several
hundred feet through the strata. The other
three sounds were accurately described, but
the machines were not identified.
Now that the war is over the bureau work
has turned to the development of the instru-
ment for peace time uses. In this connection
it is thought it may be of great value to mine
rescue crews entering mines for exploration
and to locate miners entOmbed by disaster.
The tests so far made in the vicinity of Pitts
burgh show that man pounding on the coal
y Wi a n 1hor OYs c1 doc
can be detected and located from a point 900
to 1900 feet distant This distance depends
greatly on the character of the coal which the
man is pounding, and intervening rooms and
entries seem to have surprisingly little effect
upon the distance or the determination of
direction.
Pounding with a sledge can be heard from
two to three hundred feet through the mine
cover, depending upon the quietness of the
day outside since any wind greatly interferes
with the successful operation of the instru-
ments t will at once be seen that when
mines are not too deep they can be ''eXplored'
from the surface and it will thus be possible
to find and locate a miner who is pounding.
At the Experimental mine in Bruceton, Pa,
a man has frequently been located through
one hundred and forty feet of cover within
fifty feet of the exact point where he was
pounding. study is also being made of the
distances that pounding on rails and pipes can
be heard. Since rails are generally bur-,
the earth or dust on the entries of mine and
since this dust damps the transmission of the
sound, the sounds are not transmitted very
well. The same is true of pipe lines. How
ever if pipe lines are not buried, but are laid
on blocks and ties, the pounding can be heard
great distances So far no lines have been
found long enough to show the limit of the
geophones. 1t is known, however, that thu
naked ear can get sounds farther than two
thousand feet.
1t is also thought that this device will be
of value to prevent accidents from explosions.
In this connection interesting incident
happened recently Observations were being
made at a tunnel heading. The pit boss hap
pened along and asked to be allowed to listen.
He put the ear-pieces in his ears and re-
marked MACK is tamping in a charge, we
had better move away" He spoke as natural
ly as though he had been watching Mac, and
it is quite evident that he did not realize the
sound was coming through three hundred feet
of coal, else he would not have given the
warning.