The St. Charles herald. [volume] (Hahnville, La.) 1873-1993, 1919-12-20

and more accurate various mining
operations The principle Of the microphone
applied In ascertaining In q general way the loca-
ton Of ship at sea. Toward the end OF the war
the device had been so perfected that 1t was pos
sble for the microphone listening station to cal
cuate the exact position of enemy guns after hear
ing the shots. The speed with which sound trav-
els, was. of course, known and Served as basis
Of calculations at different stations. With these
instruments electrically connected it possible
to record the exact time at which the sound
reached them and then by series Of rather in
tricate calculations based on triangulation. to
locate the object.
The geophone is based on the same principle as
the microphone, excepting that sound waves are
recorded from the earth instead of the air, ana
1t has reached such high state of development
under engineers Of the bureau of mines that 1t
bids fair to be Of the most useful applications
now being made Of inventions due to the war.
ceophone 10 seismosraph.
The geophone, though small, is essentially q
seismograph, since 1t works on the same principle
as the ponderous apparatus with which earth
quake tremOrs are recorded. 1t consists Of an
iron ring about three and half inches in dame
ter within the center Of which is suspended
lead disk that Is fastened by a single bolt through
two mica disks. one Of which covers the top and
The other the bottom Of the ring. There are two
sbfass pieces, the top one having an opening in its
center to which is fastened rubber tube leading
to stethoscopic earpiece. 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 lead weight
suspended between two mica disks cutting across
q small sair-tght box. If the instrument is placed
on the ground and anyone is pounding or digging
the vicinity, energy is transmitted as wave
ito the earth, and the earth-waves shake
fh< phone case. The lead, on account Of its
weight and because it is suspended between the
mica disks, remains comparatively motionless.
There then is produced a relative motion between
the Instruments case and the lead weight. The
result is that a compression and rarefaction of
the air in the instrument takes place. Since the
rubber tube leading the stethoscopic earpiece is
connected with this space in the geophone, this
rarefaction and compression is carried to the ear
drum. Usually two instruments are used, one for
each ear
How Direction Il Determined
When the two instruments are used. It has been
found that the sound is apparently louder from
the instrument nearer the source of the sound
It is evident then that by moving the instruments
properly point can be found when the sound
will be of the same apparent intensity In both
ears. The direction Of the sound Is then on per-
pendicuiar to the line connecting the centers OF
the two instruments either in front Of behind
the observer. Further observation viii show
which side. Direction is quite accurately de-
termined In this way. The sound Is not actually
louder in than in the other, but the ear is
capable of distinguishing the difference In time at
which the sound arrives in the two instruments.
Since this Is the case persons who are slightly
deaf In one ear are said still to be able to de-
termine direction with the instruments.
During the period Of the war. engineers Of the
mining division OF the bureau Of mines were
engaged In determining the distance that differ
ent mining machines could be heard through the
clay, shale, coal and the mine cover. Measure
ments were made also Of the energy required In
order that they might be heard definite distances
through clay. shale and coal. as we'll a. to de-