The Elk Mountain pilot., 1919-11-13

Uu 1,tiuns. The principle Of the mcrophOne was
applied In ascertaining In general way the ioca-
ito Of II ship nt sen Toward the enc, of the wnr
the device had been perfected that 1t was pos.
siln' for the micrOplOne listening station I" ca'-
cuis,e the exact position of enemy guns after hear-
"y he shots The speed with which sound trnv-
els vns Of course. known and served as a bnsis
Of calculations Mt different stations. With these
INSTRUMENTS electrically connected It was possible
I" -srord the exact time Mt which the SOUND
rrrt'ied them and then by a series of rather In
trcnte calculations bnsed on trtangulatiOn. 10
irT.te the object.
The geophone Is based the same principle as
the mlcrophone. excepting that sound waves are
recorded from she earth Instead Of the air. ana
It has reached such high state OF development
under engineers Of the bureau Of mines that II
bids fair to be one Of the most useful applications
now being made of inventions due to the war;
Geophons 10 a seisnnooraph
The geophone. though small. Is essentially
seismOgraph. since 1t works the same principle
the pOnderOus apparatus with which earth
quake tremors recorded. 1t consists OF nm
iron ring about three and half inches In dinme-
ter. within the center OF which is suspended
lend disk that Is fastened by single bolt through
two mica disks. OF which covers the top and
the other the bottom of the ring. There are two
brass pieces. the top having an opening In Its
center to which Is fastened rubber tube leading
to n stethoscopc enrpiece. 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
II small air-tight box. II the instrument In placed
on. the ground and anyone is pounding or digging
In the vicinity energy Is transmitted wave
motion TO the EARTH and the earth-waves shnke
the geophone The lead, account of Its
weight and because 1t is suspended between the
r,lca disks remains comparatively mOtionless
There then is produced Il relative motion between
the Instruments and the lead weight The
r~,suit TX that n compression and rarefaction OF
the nir in the instrument tnkes plnce. Since the
rubber tube leading the stethoscOpic earpiece is
connected with this space in the geophone. this
rnrefaction 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. 1t 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 he found when the sound
will he OF the snine apparent Intensity in both
ears The direction of the sound is then per-
pendcuiar to the line connecting the centers of
the two instruments either in front of behind
the observer. Further observation will show
which side Direction is quite accurately de-
tcrminet, In this way. The sound is not actually
louder In one than in the other. hut the Is
cspnble Of distinguishing the difference in time at
which the sound arrives in the two Instruments.
Since this is the persons who are. slightly
deaf In one said still to be able to de
termipe direction with the instruments.
During the period OF the war engineers OF the
mining division of the bureau OF mines were
cnyucp, In determining the distance that dner-
ont mining machines could he heard through the
cay shale coal and the mine cover Measure
men.s we're made also Of the energy required In
or.L~ that they might be heard definite distances
through clay. shale and coal. as well a. 10 oe-