[198]
a/^
~bz
\
+t
F(1
"
e
)
=
h0
SO'
(\
HcZ
t
=
"
I
1
-
e
HO.
,
tot
Since
M
and
c are
very
small quantities, the temperature
very
quickly
reaches the
stationary
value
SO
'
1
"*
Eo
to t
If
HO
and
O'
are
known,
a
precise
measurement of
S
can
be carried out
in this
way
in
an
absolute
manner,
otherwise, by comparing two
stationary temperatures
at
different irradiations,
a
relative
one.
Thus, there exists
a
direct relation between the deflection of
the galvanometer
x
and the radiation S.
Cx
=
I
*1*4
I
-
e
-1^
at
SO
1
1
" HO
thus SCx
=
ew
VlV4oa
By
sensitivity
one
understands of the galvanometer
one
understands
the current in
amp. necessary
to
produce
a
deflection of
1 mm.
The
sensitivity of the galvanometer in the Z[urich]
laboratory
is
1
1
~
1o1 0
.
With
an
appropriate
choice of
W1
and
W4
and
£
it is
1
1°
possible
to
detect temperature differences of
105
-
.
Resistance of
copper.
w
=
0.0157
Here the units
are
m
mm2
12
If
cm
is introduced
as
the unit in length and
cross
section,
we
obtain
w
=
0.00000157.
Hence in absolute units
w
=
1570.
116