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1
281
Heroes of the Telegraph
·
John Munro
111
The
fervent
heat
of
the
Siemens
furnace
led
the
inventor
to
devise
a
novel
means
of
measuring
high
temperatures,
which
illustrates
the
value
of
a
broad
scientific
training
to
the
inventor,
and
the
happy
manner
in
which
William
Siemens,
above
all
others,
turned
his
varied
knowledge
to
account,
and
brought
the
facts
and
resources
of
one
science
to
bear
upon
another.
As
early
as
1860,
while
engaged
in
testing
the
conductor
of
the
Malta
to
Alexandria
telegraph
cable,
then
in
course
of
manufacture,
he
was
struck
by
the
increase
of
resistance
in
metallic
wires
occasioned
by
a
rise
of
temperature,
and
the
following
year
he
devised
a
thermometer
based
on
the
fact
which
he
exhibited
before
the
British
Association
at
Manchester.
Mathiessen
and
others
have
since
enunciated
the
law
according
to
which
this
rise
of
resistance
varies
with
rise
of
temperature;
and
Siemens
has
further
perfected
his
apparatus,
and
applied
it
as
a
pyrometer
to
the
measurement
of
furnace
fires.
It
forms
in
reality
an
electric
thermometer,
which
will
indicate
the
temperature
of
an
inaccessible
spot.
A
coil
of
platinum
or
platinum-alloy
wire
is
enclosed
in
a
suitable
fire-proof
case
and
put
into
the
furnace
of
which
the
temperature
is
wanted.
Connecting
wires,
properly
protected,
lend
from
the
coil
to
a
differential
voltameter,
so
that,
by
means
of
the
current
from
a
battery
circulating
in
the
system,
the
electric
resistance
of
the
coil
in
the
furnace
can
be
determined
at
any
moment.
Since
this
resistance
depends
on
the
temperature
of
the
furnace,
the
temperature
call
be
found
from
the
resistance
observed.
The
instrument
formed
the
subject
of
the
Bakerian
lecture
for
the
year
1871.
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