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281
Heroes of the Telegraph
·
John Munro
28
One
of
Wheatstone's
most
ingenious
devices
was
the
'Polar
clock,'
exhibited
at
the
meeting
of
the
British
Association
in
1848.
It
is
based
on
the
fact
discovered
by
Sir
David
Brewster,
that
the
light
of
the
sky
is
polarised
in
a
plane
at
an
angle
of
ninety
degrees
from
the
position
of
the
sun.
It
follows
that
by
discovering
that
plane
of
polarisation,
and
measuring
its
azimuth
with
respect
to
the
north,
the
position
of
the
sun,
although
beneath
the
horizon,
could
be
determined,
and
the
apparent
solar
time
obtained.
The
clock
consisted
of
a
spy-glass,
having
a
nichol
or
double-image
prism
for
an
eye-piece,
and
a
thin
plate
of
selenite
for
an
object-glass.
When
the
tube
was
directed
to
the
North
Pole--that
is,
parallel
to
the
earth's
axis--and
the
prism
of
the
eye-piece
turned
until
no
colour
was
seen,
the
angle
of
turning,
as
shown
by
an
index
moving
with
the
prism
over
a
graduated
limb,
gave
the
hour
of
day.
The
device
is
of
little
service
in
a
country
where
watches
are
reliable;
but
it
formed
part
of
the
equipment
of
the
North
Polar
expedition
commanded
by
Captain
Nares.
Wheatstone's
remarkable
ingenuity
was
displayed
in
the
invention
of
cyphers
which
have
never
been
unravelled,
and
interpreting
cypher
manuscripts
in
the
British
Museum
which
had
defied
the
experts.
He
devised
a
cryptograph
or
machine
for
turning
a
message
into
cypher
which
could
only
be
interpreted
by
putting
the
cypher
into
a
corresponding
machine
adjusted
to
reproduce
it.
The
rapid
development
of
the
telegraph
in
Europe
may
be
gathered
from
the
fact
that
in
1855,
the
death
of
the
Emperor
Nicholas
at
St.
Petersburg,
about
one
o'clock
in
the
afternoon,
was
announced
in
the
House
of
Lords
a
few
hours
later;
and
as
a
striking
proof
of
its
further
progress,
it
may
be
mentioned
that
the
result
of
the
Oaks
of
1890
was
received
in
New
York
fifteen
seconds
after
the
horses
passed
the
winning-post.
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