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281
Heroes of the Telegraph
·
John Munro
73
To
these
gifts
of
theory,
electrical
and
mechanical,
Thomson
added
a
practical
boon
in
the
shape
of
the
reflecting
galvanometer,
or
mirror
instrument.
This
measurer
of
the
current
was
infinitely
more
sensitive
than
any
which
preceded
it,
and
enables
the
electrician
to
detect
the
slightest
flaw
in
the
core
of
a
cable
during
its
manufacture
and
submersion.
Moreover,
it
proved
the
best
apparatus
for
receiving
the
messages
through
a
long
cable.
The
Morse
and
other
instruments,
however
suitable
for
land
lines
and
short
cables,
were
all
but
useless
on
the
Atlantic
line,
owing
to
the
retardation
of
the
signals;
but
the
mirror
instrument
sprang
out
of
Thomson's
study
of
this
phenomenon,
and
was
designed
to
match
it.
Hence
this
instrument,
through
being
the
fittest
for
the
purpose,
drove
the
others
from
the
field,
and
allowed
the
first
Atlantic
cables
to
be
worked
on
a
profitable
basis.
The
cable
consisted
of
a
strand
of
seven
copper
wires,
one
weighing
107
pounds
a
nautical
mile
or
knot,
covered
with
three
coats
of
gutta-percha,
weighing
261
pounds
a
knot,
and
wound
with
tarred
hemp,
over
which
a
sheath
of
eighteen
strands,
each
of
seven
iron
wires,
was
laid
in
a
close
spiral.
It
weighed
nearly
a
ton
to
the
mile,
was
flexible
as
a
rope,
and
able
to
withstand
a
pull
of
several
tons.
It
was
made
conjointly
by
Messrs.
Glass,
Elliot
&
Co.,
of
Greenwich,
and
Messrs.
R.
S.
Newall
&
Co.,
of
Liverpool.
The
British
Government
promised
Mr.
Field
a
subsidy
of
L1,400
a
year,
and
the
loan
of
ships
to
lay
the
cable.
He
solicited
an
equal
help
from
Congress,
but
a
large
number
of
the
senators,
actuated
by
a
national
jealousy
of
England,
and
looking
to
the
fact
that
both
ends
of
the
line
were
to
lie
in
British
territory,
opposed
the
grant.
It
appeared
to
these
far-sighted
politicians
that
England,
the
hereditary
foe,
was
'literally
crawling
under
the
sea
to
get
some
advantage
over
the
United
States.'
The
Bill
was
only
passed
by
a
majority
of
a
single
vote.
In
the
House
of
Representatives
it
encountered
a
similar
hostility,
but
was
ultimately
signed
by
President
Pierce.
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