Roanoke Rapids herald. [volume] (Roanoke Rapids, N.C.) 1914-192?, 1919-11-14


applied In ascertainlng in general way the loca-
tIon of ship at sea- Toward the end of the war
the device had been so perfected that it was pos
sibe for the mcrophonc listening station To cal
culae the exact position of enemy guns after hear
ng the shots. The speed with which sound trav-
els, was, of course, known and served rs a basis
Of calculations nj different stations. With these
Instruments electrically connected II was possible
to record the exact time ut which the sound
reached them and then by series of rather in
trlcate calculations based on triangulation. TO
locate the object.
The gcophone is based on the same principle as
NE mlcrophone. excepting that sound waves are
recorded from the earth instead Of the air, and
1t has reached such n high state of development
under engineers of the bureau Of mines that II
bids fair 10 be one Of the most useful applications
now being made of inventions due to the war;
Geophone Is seismograph.
The geophone, though small, Is essentially a
selsmograph. since 1t works on the same principle
as the ponderous apparatus with which earth
quake trcmors are recorded. II consists Of an
iron ring about three and half inches in dame
ter, within the center of which Is suspended Il
lead disk that Is fastened by single bolt through
two mica disks, one of which covers the top and
the other the bottom of the ring There are two
brass pieces, the top one having an opening in Its
center to which is fastened rubber tube leading
to stethoscopc earplece. 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 hut lead weight
suspended between two mica disks cutting across
small alr-ight box. If the instrument is placed
on the ground and anyone is pounding or digging
In the vicinity, energy Is transmitted ms wave
motion 10 the earth, and the earth-waves shake
the geophone case. The lead, on account Of Its
weight and because It is suspended between the
mica disks, remains comparatively motionless.
There then is produced n relative motion between
the Instruments case and the lead weight The
result Is that compression and rarefactlon of
the air In the instrument takes place. Since the
rubber tube leading to the stethoscopc earpiece is
connected with this space In the geophOne, this
rarefactlon and compression is carried to the ear
drum. Usually two instruments are used, one for
each ear.
How Direction Is 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
1t 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-
pendlcular to the line connecting the centers of
the two instruments either in front of or behind
the observer Further observation will show
which side. Direction is quite accurately de-
termlned In this way. The sound Is not actually
louder in ear 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
termne direction with the instruments.
During the period of the war, engineers of the
mining division of the bureau of, mines We're
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, shae and coal as well as to de-