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1
378
The Story of the Atlantic Telegraph
·
Henry M. Field
316
FOOTNOTES:
[A]
The
new
method
is
thus
explained
by
Mr.
Deane:
"The
fundamental
difference
between
last
year's
system
of
testing
and
that
of
the
present
expedition
is,
that
now
all
the
ordinary
tests
for
continuity
may
be
made
simultaneously
with
the
test
for
insulation,
which
is
not
interrupted
at
all;
whereas,
last
year,
during
half
the
time
spent
in
laying
the
cable,
the
insulation
test
was
wholly
neglected.
"Last
year,
each
hour
was
divided
into
four
parts.
The
first
half
of
the
hour
was
spent
in
testing
for
insulation.
During
the
second
half,
which
was
divided
into
three
periods
of
ten
minutes
each,
tests
were
made
to
ascertain
the
resistance
of
the
conductor
and
to
prove
the
continuity
of
the
same.
All
these
tests
were
of
such
a
nature
as
to
afford
no
criterion
whatever
of
the
state
of
the
insulation
during
their
continuance,
so
that
during
the
half
of
each
hour,
or,
in
other
words,
during
half
the
time
spent
in
laying
the
cable,
the
insulation
test
was
neglected.
Also,
while
the
insulation
test
was
being
made,
there
was
no
means
of
communicating
with
the
shore,
as
the
observations
were
taken
on
board
only.
This
year,
a
test
for
insulation
is
constantly
kept
on,
and,
by
Mr.
Willoughby
Smith's
arrangement,
corresponding
observations
are
made
both
on
ship
and
shore.
At
stated
times
during
the
hour,
the
continuity
test
is
made
at
the
shore
station
by
means
of
a
condenser
applied
to
the
conductor
of
the
cable.
The
effect
of
this
is
to
increase
the
deflection
on
the
ship's
insulation
galvanometer,
thus
serving
as
a
continuity
test.
Communications
from
shore
to
ship
are
also
made
by
these
means.
The
ship
can
send
signals
to
the
shore
by
simply
reversing
the
current
for
certain
lengths
of
time,
answering
to
some
understood
code,
or
by
increasing
and
diminishing
the
tension
of
the
line,
according
to
a
preaerranged
plan.
All
these
operations
may
be
performed
without
interrupting
the
insulation
test,
except
for
a
few
seconds
while
the
current
is
being
reversed.
So
far
for
the
new
system
in
the
electrical
room
as
compared
with
last
year."
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