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1
378
The Story of the Atlantic Telegraph
·
Henry M. Field
86
Its
flexibility
is
such
as
to
make
it
as
manageable
as
a
small
line,
and
its
strength
such
that
it
will
bear,
in
water,
over
six
miles
of
its
own
weight
suspended
vertically.'
The
conducting
medium
consists
not
of
one
single
straight
copper-wire,
but
of
seven
wires
of
copper
of
the
best
quality,
twisted
round
each
other
spirally,
and
capable
of
undergoing
great
tension
without
injury.
This
conductor
is
then
enveloped
in
three
separate
coverings
of
gutta-percha,
of
the
best
quality,
forming
the
core
of
the
cable,
round
which
tarred
hemp
is
wrapped,
and
over
this,
the
outside
covering,
consisting
of
eighteen
strands
of
the
best
quality
of
iron-wire;
each
strand
composed
of
seven
distinct
wires,
twisted
spirally,
in
the
most
approved
manner,
by
machinery
specially
adapted
to
the
purpose.
The
attempt
to
insulate
more
than
one
conducting-wire
or
medium
would
not
only
have
increased
the
chances
of
failure
of
all
of
them,
but
would
have
necessitated
the
adoption
of
a
proportionably
heavier
and
more
cumbrous
cable.
The
tensile
power
of
the
outer
or
wire
covering
of
the
cable,
being
very
much
less
than
that
of
the
conductor
within
it,
the
latter
is
protected
from
any
such
strain
as
can
possibly
rupture
it
or
endanger
its
insulation
without
an
entire
fracture
of
the
cable."
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