The Idaho Springs siftings-news., 1919-11-14

on. cations The principle of the microphone
Applied in ascertanng in a general way the loca-
tou of n ship at Toward the end of the war
the device had been perfected that it was pos
sibN for the microphone listening station to cal
cus tie the exact position of enemy guns after near
ing the shots The speed with which sound trav-
els was, of course, known and served as a OASIS
Of calculations at different stations With these
Instruments electrically connected 1t was 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 mcrophone. excepting that sound waves are
recorded from the earth instead of the air. and
1t has reached such high state of development
under engineers of the bureau of mines that 1t
bids fair to be one of the useful applications
now being made of inventions due to the war.
Geophone Is sesmoeraph.
The geophone though small is essentially
sesmograph, since it works on the same principle
the ponderous apparatus with which earth
quake tremors recorded 1t consists of an
iron ring about three and half inches in diane
ter. within the center of which is suspended
lead disk that is fastened by single bolt through
two mica disks, of which the top and
the other the bottom of the ring. There two
brass pieces, the top having an opening in its
center to which is fastened rubber tube leading
to a stethoscopic earpiece. These cap pieces are
fastened with bolts to the iron ring also
to hold the mica disks in place.
We then have really nothing but lead weight
suspended between two mica disks cutting across
a small airtight box. If the instrument is placed
the ground and anyone is pounding or digging
in the vicinity. energy is transmitted as
motion to the earth. and the earth-waves shake
the geophone case. The lead on account of its
weight and because 1t is suspended between the
mica disks, remains comparatively motionless
There then is produced relative motion between
the Instruments and the lead weight. The
result is that compression and rarefacton of
the air in the instrument takes place Since the
rubber tube leading to the stethoscopic earpiece is
connected with this space in the geophone, this
rarefaction and compression is carried to the
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
II is evident then that by moving the instruments
properly n 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 a per-
pendicuar 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-
termined in this way. The sound is not actually
louder in one 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 he heard definite distances
through clay. shale and coal, well as to de-