St. Johnsbury Caledonian. [volume] (St. Johnsbury, Vt.) 1867-1919, 1879-12-19
Wonderful ]


was overheard in the cars few day.
ago, that ''electricity had nothing to dc
with the telephone" and the though
may be shared by many, so that il
these times when inquiry is so common
as to the reason of things, it may not bt
amiss to some to know something more
of the principles employed in the tele
phone.
These principles may be readily IN.
dersto0d by any one in spite of the as,
sertion sometimes made that they in.
volve distractions only comprehended
by experts.
We should carefully distinguish be,
tween the string or acoustic telephone
and the electric telephone, that in most
common use. There is no more SINH
larity in principle between the two than
between a speaking tube and tele-
graph. The speaking tube and the
acoustic telephone both convey vibra-
tions of voice bodily, as it were, from
place to place, the one through the air
of the tube, the other through the string
or wire stretched from one diaphragm
to the other.
People sometimes think no electricity
is concerned in the other kind of tele-
phone because it is worked without
battery, the battery being used
merely to call. Here we come to a
principle which needs little explana-
ton.
If coil of insulated wire be put over
the end of magnet any change in the
magnetism of the magnet will produce
a current of electricity in the wire. A
change of magnetism is produced by the
movement of a piece of iron near the
magnet. In telephone we have these
conditions. There is coil of wire around
the end of a magnet and piece of iron,
Put telephone in circuit with a gal
vanometer sufficiently delicate, and
press your finger on the diaphragm and
the galvanOmeter indicates the current
We usually move the diaphragm by
speaking against it. So we make the
electric currents by speaking. But how
many? Just as many as the number of
vibrations in the tones of the voice, or
whatever sound is made near the dia-
phragm, or probably just twice as many,
for movement of the diaphragm one
way makes a current in one direction,
and as it moves back another current is
produced in the other direction. Vibra-
tons are made at constantly varying
rates in ordinary speech, and with ev-
cry complex variation in rate, intensity
and amplitude, there are the infinitely
varying currents of electricity, and
these go through the whole circuit,
and in the telephone at the other end
their ever changing phases reproduce
a sound at that end which faithfully
copies the original sound. So we see
that no sound goes through the wire, but
hundreds or thousands of different cur
rents of electricity per second, caused
by the sound at one end and making a
sound at the other end by their effects
on the magnet and diaphragm.
There is another class of instruments
in which similar effects are produced
by another means. This is the class of
microphones and carbon telephones.
In these an ordinary current from a
battery is used, but it is made to vary
its force by the vibrations of the voice.
This is done by some kind of loose con-
tact, or light touch of substances, gen
orally carbon, between which the cur
rent passes with varying ease as it is
shaken by the voice.
Several forms of this apparatus may
easily be made so delicate as to give
indications of so light touch as a f1y's
foot, but it is not so easy to make them
sensitive and yet susceptible of all the
variations of the voice. This is excel
lently accomplished in the Blake Trans
mitter, which will so perfectly take up
the voice that one speaking several feet
away from the transmitter can be heard
by means of a telephone at the other
end of the line, as well as though the
person speaking stood in the same
room.
There is another wonderful capacity
of electricity made use of in this instru-
ment. The battery circuit of electricity
does not pass through the line and the
telephones at all. When a current of
electricity is started or stopped in a
wire, in another wire by the side of the
first, but perfectly insulated from it,
another current of electricity is produc-
ed. The latter is called an induced cur
lent. In the Blake Transmitter the
current is passed through the inner coil
of an induction coil, and then through
the light contact of two small springs
which press against an iron diaphragm,
and this diaphragm receives the I'M
pulse of the voice. The telephone is in
circuit with the outer or secondary coil,
so that all the electricity operating the
telephones is from induced currents, not
from the battery directly. The sensi-
tiveness of the telephone to induced
currents of electricity accounts for the
fact noticed in their use that telegraph
ing can be overheard at 50 great dis
lance. The passage of the charge of
electricity from a battery produces a