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281
Heroes of the Telegraph
·
John Munro
174
This
apparatus
was
completed
on
June
2,
1875,
and
the
same
day
he
succeeded
in
transmitting
SOUNDS
and
audible
signals
by
magneto-electric
currents
and
without
the
aid
of
a
battery.
On
July
1,
1875,
he
instructed
his
assistant
to
make
a
second
membrane-receiver
which
could
be
used
with
the
first,
and
a
few
days
later
they
were
tried
together,
one
at
each
end
of
the
line,
which
ran
from
a
room
in
the
inventor's
house
at
Boston
to
the
cellar
underneath.
Bell,
in
the
room,
held
one
instrument
in
his
hands,
while
Watson
in
the
cellar
listened
at
the
other.
The
inventor
spoke
into
his
instrument,
'Do
you
understand
what
I
say?'
and
we
can
imagine
his
delight
when
Mr.
Watson
rushed
into
the
room,
under
the
influence
of
his
excitement,
and
answered,'Yes.'
A
finished
instrument
was
then
made,
having
a
transmitter
formed
of
a
double
electro-magnet,
in
front
of
which
a
membrane,
stretched
on
a
ring,
carried
an
oblong
piece
of
soft
iron
cemented
to
its
middle.
A
mouthpiece
before
the
diaphragm
directed
the
sounds
upon
it,
and
as
it
vibrated
with
them,
the
soft
iron
'armature'
induced
corresponding
currents
in
the
cells
of
the
electro-magnet.
These
currents
after
traversing
the
line
were
passed
through
the
receiver,
which
consisted
of
a
tubular
electro-magnet,
having
one
end
partially
closed
by
a
thin
circular
disc
of
soft
iron
fixed
at
one
point
to
the
end
of
the
tube.
This
receiver
bore
a
resemblance
to
a
cylindrical
metal
box
with
thick
sides,
having
a
thin
iron
lid
fastened
to
its
mouth
by
a
single
screw.
When
the
undulatory
current
passed
through
the
coil
of
this
magnet,
the
disc,
or
armature-lid,
was
put
into
vibration
and
the
sounds
evolved
from
it.
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