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1
378
The Story of the Atlantic Telegraph
·
Henry M. Field
377
Perfect
as
this
instrument
seemed,
yet
after
further
years
of
study
and
experiment,
Sir
William
Thomson
was
able,
at
the
close
of
1883,
to
present
to
the
world
the
Siphon
Recorder,
greatly
improved,
because
in
a
very
much
simpler
form.
In
this
form
of
the
instrument,
instead
of
the
electro-magnets,
he
used
two
bundles
of
long
bar-magnets
of
square
section
and
made
up
of
square
bars
of
glass-hard
steel.
The
two
bundles
are
supported
vertically
on
a
cast-iron
socket,
and
on
the
upper
end
of
each
is
fitted
a
soft
iron
shoe,
so
shaped
as
to
concentrate
the
lines
of
force
and
thus
produce
a
strong
magnetic
field
in
the
space
within
which
the
signal-coil
is
suspended.
He
made
instruments
of
this
kind
to
work
both
with
and
without
electrification
of
the
ink.
Without
electrification
the
instrument,
as
shown
in
Fig.
2,
is
exceedingly
simple
and
compact,
and
in
this
form
is
capable
of
doing
good
work
on
cables
of
lengths
up
to
500
or
600
miles.
When
constructed
for
electrification
of
the
ink,
as
shown
in
Fig.
3,
it
is
of
course
available
for
much
longer
lengths
of
cable,
but
for
cables
such
as
the
Atlantic
cables,
the
original
form
of
the
Siphon
Recorder
is
that
still
chiefly
used.
The
strongest
magnetic
field
hitherto
obtained
by
permanent
magnets
(of
glass-hard
steel)
is
about
3000
C.
G.
S.
With
the
electro-magnets
of
the
original
form
of
Siphon
Recorder
as
in
ordinary
use
a
magnetic
field
of
about
or
over
5000
C.
G.
S.
is
easily
attained.
In
Fig.
4
is
shown
a
fac
simile
of
part
of
a
message
received
and
recorded
by
a
Siphon
Recorder,
such
as
is
shown
in
Fig.
1,
from
one
of
the
Eastern
Telegraph
Co.'s
Cables
of
about
830
miles
length.
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