one
obtains almost the
same
numbers
as
when
one measures
q
using
the
units given above
(q
=
1-w).
w
The thickness of wires is measured
using
micrometers.
1
It is
possible
to read off
2000
mm.
Measuring
the
temperature by measuring
the resistance.
Since measurement of resistance is to be done with
precision,
and
resistance is related
to
temperature in
a
simple
way
and varies with
temperature relatively quickly,
it
can
be used for the determination
of the
temperature.
To
measure
the temperature at locations that
are
not easily
accessible because of their distance
or
other
circumstances,
the
following
one uses
a
method of measurement
according
to the
following
scheme:
[Fig.]
We
vary
the resistor
N
until l1
=
l2
=
l.
Further,
let
us
have
K1
=
K2
=
K3
=
K.
Then:
N + K
JL
•
w
+ K +
n
N
=
w
+
n,
where
n
is known.
"
N " "
Thus
we
obtain
w.
However,
w
=
w0(l
+
at)
t
=
^
w0a
The temperature
at
the bottom of the
sea,
for example,
can
be measured
in this
way,
as
well
as
the temperature in blast furnaces
or
chimneys.
The
measuring
wire
w
is then to be chosen in the
following
way.
[Fig.]
porcelain
The electrical method of measurement enables
us
to
measure
minute
temperature differences and is therefore suitable for the detection
and measurement of heat
radiation.
How [A?] sensitive resistance
w.
is then built by using
a
large
number of
finely
rolled-out metal
strips
(tin foils) connected in
series.
[Fig.]
We
investigate
the
course
of the
process
with one-sided irradiation.
114