The silver state news. [volume] (Winnemucca, Nev.) 1907-1909, 1909-01-16

ated in the air. These movements l,l
the air which excite our sense of hear
ing must be quite clearly understood
IL we would understand the operation
of any sound producing apparatus.
In most eases we can quite readily
nerceiye that a sound producing body
Il in a state of vibration. These vi
brations of sounding piano string
can be seen and felt. But vibrating
body in order to cause the sensation
of sound, must transmit its motion to
the ear through the medium of the
air. When a bell rings, the surround
ing air is alternately compressed and
rarified, with the result that pulsations
of the air or sound waves are sent out
in all directions. As an example,
middle G on piano vibrates 256 times
per second This vibrating wire sends
out ESQ pulses of air per second all
of which impinge on the ear. The
membrane of the ear is thereby made
to yibrate 256 times per second. These
vibrations are transmitted to the aud
itory nerves and the brain interprets
them as soud sensation of definite
pitch, loudhess. and quality.
There is a disc Of metal or other
elastic material in a telephone trans
mitter that responds to air vibrations,
moving in unison with the air waves
that impinge on it. In this respect At
is essentially like the membrane of
the ear.
II must not be thought that these
vibrations are passed on over the
telephones wires. But the telephone,
by means of the electric current, does
produce secondary sound waves in the
receiver that are in all essential re-
speets like the primary sound-wavrs
of the transmitter. As these second
ary sound waves from the receiver
strike the membrane of the ear of the
hstener they are heard just as the
primary sound-waves would be heard.
The transmitter is. of course, that
part of the telephone we talk into and
the receiver is that part we hold to
the ear. Perhaps ii would be well to
describe these parts in little more
detail.
The transmitters now in use are
called "variable resistance trans
mitters. Their essential parts are (D
the elastic diaphram upon which the
soundwaves impinge and behind
which lie (2)--loose carbon contacts.
often in the form of small grains. The
receiver consists of a (D--strong per
manent magnet, Ca small coil of
insulated wire surrounding one end of
the magnet and Ga diaphram Ga
thin sheet of soft irony placed very
near but not in contact with the
magnet and the coil The essentioE
parts of the transmitter and the ~
ceiver are protected and supported by
case.
Through the transmitter, over the
telephone wire, through the receiver,
and back Offer return wire to the
transmitter again, there flows very
weak current furnished usually by
few dry cells.
Let us now see what role this elec-
uric current plays. We have already
noted that the telephone wire does not
transmit sound-waves. 1t does transmit
puisating (varying) currents which
correspond in frequency to that Of the
sound-waves. 1t is the part of the
transmitter to produce this variation
IN the current strength.
Those who have had any practical
experience with electricity know thar
tue effect of a loose contact between
any two parts of circuit is to in
crease the resistance and thereby
weaken the current. But this effect
Is very much more than usually notice
apie II the parts are carbon, as they
are in the transmitter Sound-waves
on the diaphram of the transmittef
cause varying pressure on the carbon
grains back of the transmitter and
thereby variation in the resistance
10 the current that is passing through
the carbon grains. The resulang
variations in resistance cause instant
variations Of current.
These fiuctuating current coming
over the line pass through the insula
TED wire coil in the receiver and thus
vary the magnetic field strength This,
IN turn, varies the normal pull of the
magnet upon thin disc or diaphram and
as result the diaphram is caused 20
Viprate in accordance with the undula
tory currents sent over the line. The
IKE vibrations of the receiver dia
pnram produce as an effect soundwaves
In the air like the causal air sound