DOC.
14
PROOF
OF
AMPERE'S
CURRENTS
183
706
with
the theoretical
one.
If
we
take 1200 for the
magnetisation
reached
by
the
iron,
we get (the
volume
of the
cylinder being
0,16
cm3)
Is
=
192.
By
direct
observation
of
the oscillations in
the alter-
nating
field
we
found
K
=
0,533.
As
Q =
0,0065,
it follows
from
(16)
that
|«|
=
0,0036.
For
a
scale
distance of 45
cm
this
gives
for
the
double deviation
4|a|
.45
=
0,65;
as
has been
said
already, we
have found
0,45
by
our
experiments.
As
to
this difference
we
must
observe
that
the
theoretical
value
is
an upper
limit,
as
the
magnetism
does not
change
its
sign
in-
stantaneously.
On account
of the
demagnetising
influence
of the free
poles
the
field
in the
coil must be
rather
strong
if
on
its
reversal the
mag-
netisation
is
to
take
immediately
a
constant
value in the
new
direction.
$
6. Determination of
the
phase.
We have
seen
that the active
couple
differs
a
quarter
of
a period
in
phase
from
the
alternating
magnetisation.
Further it follows
from
$
3 that
by
comparing
the
phase
of the
effect
(P1)
with that
of
the
alternating
current
(P2) we
shall be
able
to
decide,
whether the
electrons
circulating
round
the iron
molecules
are
really
negative
ones.
We
have tried to effect this
by
proceeding
in
the
following way.
The
single
wire
lamp
used
for
the
scale
reading
was
connected
with the main
alternating
current conductors
in
parallel
with the
coil
that contained the
iron
cylinder.
If
then
we
brought a
perma-
nent
magnet
near
the
lamp,
the
incandescent wire
was
set
into
motion
by
alternating
electromagnetic
forces,
so
that, besides
the
oscillations
due
to
the
vibrations of the
mirror, the
image
also
performed
those
that
were
caused
by
the
motion
of the wire.
By
observing
whether
the
addition of
this last
vibration increased
or
decreased
the
amplitude
of the
image, we
could
compare
the
phase P1
with that
of
the
new
vibrations. Now
this
latter
is
deter-
mined
by
the
phase
of
the
glowing
wire and
this
in
its turn
depends
on
the
phase
of
the
current
in
it,
whereas
the
difference
between
this
phase
and
P2
is
determined
by
the
self-induction of the
coil.
It would therefore be
possible
to
compare
the
phases
P1
and
P2.
Unfortunately,
when
our
experiments
had been
brought
to
a
con-
clusion and
one
of
us
had left Berlin
it
came
out that
a
mistake
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