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281
Heroes of the Telegraph
·
John Munro
171
Mr.
Elisha
Gray,
of
Chicago,
also
devised
a
tone
telegraph
of
this
kind
about
the
same
time
as
Herr
La
Cour.
In
this
apparatus
a
vibrating
steel
tongue
interrupted
the
current,
which
at
the
other
end
of
the
line
passed
through
the
electro-magnet
and
vibrated
a
band
or
tongue
of
iron
near
its
poles.
Gray's
'harmonic
telegraph,'
with
the
vibrating
tongues
or
reeds,
was
afterwards
introduced
on
the
lines
of
the
Western
Union
Telegraph
Company
in
America.
As
more
than
one
set
of
vibrations--that
is
to
say,
more
than
one
note--can
be
sent
over
the
same
wire
simultaneously,
it
is
utilised
as
a
'multiplex'
or
many-ply
telegraph,
conveying
several
messages
through
the
same
wire
at
once;
and
these
can
either
be
interpreted
by
the
sound,
or
the
marks
drawn
on
a
ribbon
of
travelling
paper
by
a
Morse
recorder.
Gray
also
invented
a
'physiological
receiver,'
which
has
a
curious
history.
Early
in
1874
his
nephew
was
playing
with
a
small
induction
coil,
and,
having
connected
one
end
of
the
secondary
circuit
to
the
zinc
lining
of
a
bath,
which
was
dry,
he
was
holding
the
other
end
in
his
left
hand.
While
he
rubbed
the
zinc
with
his
right
hand
Gray
noticed
that
a
sound
proceeded
from
it,
which
had
the
pitch
and
quality
of
the
note
emitted
by
the
vibrating
contact
or
electrotome
of
the
coil.
'I
immediately
took
the
electrode
in
my
hand,'
he
writes,
'and,
repeating
the
operation,
found
to
my
astonishment
that
by
rubbing
hard
and
rapidly
I
could
make
a
much
louder
sound
than
the
electrotome.
I
then
changed
the
pitch
of
the
vibration,
and
found
that
the
pitch
of
the
sound
under
my
hand
was
also
changed,
agreeing
with
that
of
the
vibration.'
Gray
lost
no
time
in
applying
this
chance
discovery
by
designing
the
physiological
receiver,
which
consists
of
a
sounding-box
having
a
zinc
face
and
mounted
on
an
axle,
so
that
it
can
be
revolved
by
a
handle.
One
wire
of
the
circuit
is
connected
to
the
revolving
zinc,
and
the
other
wire
is
connected
to
the
finger
which
rubs
on
the
zinc.
The
sounds
are
quite
distinct,
and
would
seem
to
be
produced
by
a
microphonic
action
between
the
skin
and
the
metal.
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