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281
Heroes of the Telegraph
·
John Munro
72
The
speed
of
a
signal
through
the
conductor
of
a
submarine
cable
is
thus
diminished
by
a
drag
of
its
own
making.
The
nature
of
the
phenomenon
was
clear,
but
the
laws
which
governed
it
were
still
a
mystery.
It
became
a
serious
question
whether,
on
a
long
cable
such
as
that
required
for
the
Atlantic,
the
signals
might
not
be
so
sluggish
that
the
work
would
hardly
pay.
Faraday
had
said
to
Mr.
Field
that
a
signal
would
take
'about
a
second,'
and
the
American
was
satisfied;
but
Professor
Thomson
enunciated
the
law
of
retardation,
and
cleared
up
the
whole
matter.
He
showed
that
the
velocity
of
a
signal
through
a
given
core
was
inversely
proportional
to
the
square
of
the
length
of
the
core.
That
is
to
say,
in
any
particular
cable
the
speed
of
a
signal
is
diminished
to
one-fourth
if
the
length
is
doubled,
to
one-ninth
if
it
is
trebled,
to
one-sixteenth
if
it
is
quadrupled,
and
so
on.
It
was
now
possible
to
calculate
the
time
taken
by
a
signal
in
traversing
the
proposed
Atlantic
line
to
a
minute
fraction
of
a
second,
and
to
design
the
proper
core
for
a
cable
of
any
given
length.
The
accuracy
of
Thomson's
law
was
disputed
in
1856
by
Dr.
Edward
O.
Wildman
Whitehouse,
the
electrician
of
the
Atlantic
Telegraph
Company,
who
had
misinterpreted
the
results
of
his
own
experiments.
Thomson
disposed
of
his
contention
in
a
letter
to
the
ATHENAEUM,
and
the
directors
of
the
company
saw
that
he
was
a
man
to
enlist
in
their
adventure.
It
is
not
enough
to
say
the
young
Glasgow
professor
threw
himself
heart
and
soul
into
their
work.
He
descended
in
their
midst
like
the
very
genius
of
electricity,
and
helped
them
out
of
all
their
difficulties.
In
1857
he
published
in
the
ENGINEER
the
whole
theory
of
the
mechanical
forces
involved
in
the
laying
of
a
submarine
cable,
and
showed
that
when
the
line
is
running
out
of
the
ship
at
a
constant
speed
in
a
uniform
depth
of
water,
it
sinks
in
a
slant
or
straight
incline
from
the
point
where
it
enters
the
water
to
that
where
it
touches
the
bottom.
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