The Topeka state journal. [volume] (Topeka, Kansas) 1892-1980, 1919-04-14
TOPEKA STATE JOURNAL
INFORM ALTON
BURE AU
FREDERIC :. HAsK1N. Director.
washineton, d. c
THE GEoPHONE.

Wonderful things are DelnS accom-
plished by that war device known as
the Geophone, which was invented for
locating artillery fire, and is now be-
ing applied by the Bureau of Mines
to variety of peaceful purposes.
These purposes vary all the way
from locating a knock in the cylinder
of an engine to- locating miner en-
tombed in a mine as the result of an
explosion.
one recent feat of the geophone
was performed in connection with the
digging of a tunnel thru mountain.
Two excavations had been started
from opposite directions, but they fail
ed to meet because of some mistake
in the plans. The engineers under
ground were unable to tell why they
had missed each other or by how
much They faced the prospect of
tunne1ing at random in various di-
rections until they met by accident
But the geophone solved the problem
by locating the end of each tunnel
precisely from a position on the
ground above. 4
The great value of the geophone
lies in this fact that it not only hears
| sounds thru the earth, but locates the
cause with surprising accuracy. This
mocha meal ear thus accomplishes
what the human ear is unable to do.
Alan Leighton. assistant chemist of
the bureau, who now has charge of
these Investigations for the bureau
has given the following statement of
general information regarding the
geophone:
The instrument, tho small, is es-
sentially seismograph, since it works
on the same principle as the ponder
Gus a apparatus with which earthquake
tremors are recorded.
1t consists of an iron ring about
three and one-half inches in diam
eter, within the center OF which is
1aad disk faStepad nv a
single bolt thru two mica disks, one
of which covers the top and the other
the bottom of the ring. There then
are two brass cap pieces, the top one
having an opening in its center to
which is fastened a rubber tube,
leading to a stethoscopic ear piece.
These cap pieces are fastened with
bolts to the iron ring and serve also
to hold the mica disks in place.
We then have really nothing but
a lead weight suspended between two
mica disks across a small alright
box If the instrument is placed on
the ground and any one is pounding
or digging in the vicinity, energy IS
ira nsmitted as wave motion to the
earth, and the earth-waves shake the
geophone case. The lead weighs, on
account of it's mass, and because it
is suspended between the mica plates,
remains comparatively motionlesS.
There then is produced a relative mo-
ton between the instrument case and
the lead weight. The result is that
a disturbance of the air in the in
strument takes place. Since the rub
Der tube leading to the stethoscopic
ear piece is connected with this space
in the geophone, this disturbance is
carried to the ear drum.
Two instruments are usedI one for
each ear, and the sound is appar-
entity louder from the instrument
nearer the source of the sound. 1t
is evident. then, that by moving the
instrument properly, point can be
found where the sound will be of
the same apparent intensity in both
ears. The direction of the sound is
then on a perpendicular to the line
connecting the centers of the two
instruments either in front of or be-
hind the observer. Further observa-
ton will show which side. Direction
is quite accurately determined in this
way.
During the period of the war, en-
gineers of the mining division of the
bureau of mines were engaged in de-
termining the distance that different
mining machines could be heard thru
the clay shale. coal and the mine
cover. Measurements were made also
of the energy required in blows that
they be heard definite distances thru
distances at which the shock waves
resulting from the discharge of vari-
Gus explosives could be heard. A
| brief investigation of the factors in
fluencing the transfer of energy from
a mining tool to the clay and coal was
! also made in order that recommends
| lions 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 it was found that
| sounds were transmitted only about
half as far in clay as in sha1e 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 q pick on
| the bituminous coal can be detected
| for distance of nine hundred feet,
and the direction determined, and that
pounding with a sledge can be heard
| as 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 harder than in most other
| bituminous coal beds. The explosion
of one-ounce charge of dynamite was
| detected distance of over two thou
sand feet thru the shale strata.
One interesting feature of the in
| struments is that the sound as trans
mitted to the ear is very characteristic
| or the instrument producing the
j 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 operated was able to
! recognize and name nine of the in
| struments at distance of several
| hundred feet thru the strata. The
other three sounds were accurately de-
scribed. but the machines were not
| Identified.
Now that the war is over the bureau
work has turned to the development
OF the instrument 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 tc
locate miners entombed by disaster