New Mexico state record. (Santa Fe, N.M.) 1914-19??, 1919-11-14

operations. Inc principle OF tle mlcroInone WIS
applied in ascertaining In a general way the loca-
tion of Il ship at sea. Toward the end of the war
the device had been so perfected that it was pos
sible for the microphone listening station 10 cal
culato 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 Il basis
Of calculations AT different stations. With these
Instruments electrically connected it was possible
to record the exact time at which the sound
reached them ana then, by a series of rather In
tricate calculations based on triangulation, to
locate the object.
The %geophonc is based on the same principle as
the microphonc, excepting that sound waves ARE
recorded from the earth instead of the air, and
IT has reached such a high state of development
under engineers of the bureau of mines that it
bids fair to be one of the most useful applications
now being made of inventions due to the war.
o~eophone is a seismosraph.
The g%cophonc. though small. is essentially a
seisinograph, since it works on the same principle
rs the ponderous apparatus with which earth
quake trcmorS are recOrded. Ii consists of an
iron ring about three and II half inches in diame-
ter. within the center Of which is suspended n
lead disk that Is fastened by IA 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 a rubber tube leading
10 a 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 a lead weight
suspended between two mica disks cutting across
n small air-tight box. If the instrument is placed
on the ground and anyone is pounding or digging
In the vicinity. energy is transmitted as wave
motion ia the earth. and the earth-waves shake
the geophone ease. The lead. on account of its
weight and because 1t is suspended between the
mica disks, remains comparatively motionless.
TIa., .1A., L., .-ln,, N r,Inyi- a.tfn, lnt....n,
the Instruments case and the lead weight. The
result is that a compression and rarefactlon OF
the air in the instrument takes place. Since the
rubber tube leading to the stethoscopic earpiece Is
with this space in the %geophone. this
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 il evident then that by moving the instruments
properly a point can be found when the sound
be of the same apparent intensity in both
ears. The direction of the sound is then on a per-
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-
IN this way. The sound is not actually
louder In one ear than in the other, but the ear is
capable Of distinguishing the difference in time at
which the sound arrives i'm the two instruments.
Since this is the case. persons who are slightly
leaf 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 we're
sngaged in determining the distance that differ
mt mining machines could be heard through the
lay. shale. coal and the mine cover. Measure
nents we're made also Of the energy required in
49, 41.a. thar rufuIt ba heard dQfnffp distances
through clay, shaIe and coal. as well as TO de-