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Heroes of the Telegraph
·
John Munro
21
The
five-needle
telegraph,
which
was
mainly,
if
not
entirely,
due
to
Wheatstone,
was
similar
to
that
of
Schilling,
and
based
on
the
principle
enunciated
by
Ampere--that
is
to
say,
the
current
was
sent
into
the
line
by
completing
the
circuit
of
the
battery
with
a
make
and
break
key,
and
at
the
other
end
it
passed
through
a
coil
of
wire
surrounding
a
magnetic
needle
free
to
turn
round
its
centre.
According
as
one
pole
of
the
battery
or
the
other
was
applied
to
the
line
by
means
of
the
key,
the
current
deflected
the
needle
to
one
side
or
the
other.
There
were
five
separate
circuits
actuating
five
different
needles.
The
latter
were
pivoted
in
rows
across
the
middle
of
a
dial
shaped
like
a
diamond,
and
having
the
letters
of
the
alphabet
arranged
upon
it
in
such
a
way
that
a
letter
was
literally
pointed
out
by
the
current
deflecting
two
of
the
needles
towards
it.
An
experimental
line,
with
a
sixth
return
wire,
was
run
between
the
Euston
terminus
and
Camden
Town
station
of
the
London
and
North
Western
Railway
on
July
25,
1837.
The
actual
distance
was
only
one
and
a
half
mile,
but
spare
wire
had
been
inserted
in
the
circuit
to
increase
its
length.
It
was
late
in
the
evening
before
the
trial
took
place.
Mr.
Cooke
was
in
charge
at
Camden
Town,
while
Mr.
Robert
Stephenson
and
other
gentlemen
looked
on;
and
Wheatstone
sat
at
his
instrument
in
a
dingy
little
room,
lit
by
a
tallow
candle,
near
the
booking-office
at
Euston.
Wheatstone
sent
the
first
message,
to
which
Cooke
replied,
and
'never,'
said
Wheatstone,
'did
I
feel
such
a
tumultuous
sensation
before,
as
when,
all
alone
in
the
still
room,
I
heard
the
needles
click,
and
as
I
spelled
the
words,
I
felt
all
the
magnitude
of
the
invention
pronounced
to
be
practicable
beyond
cavil
or
dispute.'
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