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281
Heroes of the Telegraph
·
John Munro
176
The
primitive
telephone
has
been
greatly
improved,
the
double
electro-magnet
being
replaced
by
a
single
bar
magnet
having
a
small
coil
or
bobbin
of
fine
wire
surrounding
one
pole,
in
front
of
which
a
thin
disc
of
ferrotype
is
fixed
in
a
circular
mouthpiece,
and
serves
as
a
combined
membrane
and
armature.
On
speaking
into
the
mouthpiece,
the
iron
diaphragm
vibrates
with
the
voice
in
the
magnetic
field
of
the
pole,
and
thereby
excites
the
undulatory
currents
in
the
coil,
which,
after
travelling
through
the
wire
to
the
distant
place,
are
received
in
an
identical
apparatus.
[This
form
was
patented
January
30,
1877.]
In
traversing
the
coil
of
the
latter
they
reinforce
or
weaken
the
magnetism
of
the
pole,
and
thus
make
the
disc
armature
vibrate
so
as
to
give
out
a
mimesis
of
the
original
voice.
The
sounds
are
small
and
elfin,
a
minim
of
speech,
and
only
to
be
heard
when
the
ear
is
close
to
the
mouthpiece,
but
they
are
remarkably
distinct,
and,
in
spite
of
a
disguising
twang,
due
to
the
fundamental
note
of
the
disc
itself,
it
is
easy
to
recognise
the
speaker.
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