and
G an
inserted
galvanometer.
gypsum
[Fig.]
cooling
apparatus
We
have
then
€
=
At
£
A
.
KI1
W
=
V
x =
tg
x =
Bi
=
t
Thus,
up
to about
10°
the
angle
of
deflection
can
be taken
as
proportional
to the temperature difference.
For
objective
presentation
one can
use a concave
mirror that is
rigidly
connected
with
the mobile magnet.
To obtain
a
line of light
one uses
a
suitable incandescent lamp.
scale [Fig.]
112
Let the
lamp be
in
A.
When the
condition
_
+

is
satisfied,
a
a
b
r
real image of the incandescent filament
is
produced
on
the
scale.
If
n
is the
number of scale
divisions
of
length
A,
we
have
tg 2x
=
2x
=
n
A
D
Since
only
quotients
of
temperatures
appear
in the expression for
k,
the
method is
a
relative
one.
t1
_
x1
=
n1_
t2
x2 n2
Thus
we
have
1
*
.x1.
k = t•
lg
(

)•R2
Az x2
7T
The
performed
test series
yielded
the
following
values for 15second
time
intervals:
t1
t2
16.5
^
The quotients
vary
between 1.89 and 1.5.
15.9
ji
The
validity
of the law has thus been proved.
14.5
13
11.7
10.5
9.6
8.7
7.1.
in
Jin
Jl!jiii
38