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378
The Story of the Atlantic Telegraph
·
Henry M. Field
233
The
great
problem
had
been
to
combine
strength
with
flexibility.
Mere
dead
weight
was
an
objection.
The
new
cable,
though
nearly
twice
as
heavy
as
the
old
in
air,
when
immersed
in
water,
weighed
but
a
trifle
more;
so
that
it
was
really
much
lighter
in
proportion
to
its
size.
This
increased
lightness
was
a
very
important
matter
in
laying
the
cable,
as
it
caused
it
to
sink
slowly.
The
old
cable,
though
smaller,
was
heavy
almost
as
a
rod
of
iron,
so
that,
as
it
ran
out,
it
dropped
at
an
angle
which
exposed
it
to
great
danger
in
case
of
a
sudden
lurch
of
the
ship.
Thus
in
1857
it
was
broken
by
the
stern
of
the
Niagara
being
thrown
up
on
a
wave
just
as
the
brakes
were
shut
down.
Now
the
cable,
being
partially
buoyed
by
the
rope,
would
float
out
to
a
great
distance
from
the
ship,
and
sink
down
slowly
in
the
deep
waters.
By
this
combination
of
rope
and
iron,
a
cable
was
secured
two
and
a
half
times
as
strong
as
the
old--the
breaking
strain
of
the
former
having
been
three
tons
five
cwt.,
and
of
the
latter
seven
tons
and
fifteen
cwt.
Or,
to
put
it
in
another
form,
the
contract
strain
of
the
former
was
less
than
five
times
its
own
weight
per
mile
in
water;
so
that
if
the
cable
had
been
laid
in
some
parts
of
the
Atlantic,
where
the
ocean
is
more
than
five
miles
deep,
it
would
have
broken
under
the
enormous
strain.
But
the
contract
strain
of
the
new
cable
was
equal
to
eleven
times
its
weight
per
mile
in
water,
which,
as
the
greatest
depth
of
water
to
be
passed
was
but
two
and
a
half
miles,
rendered
the
cable
more
than
four
times
as
strong
as
was
required.
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