188
DOC. 14 PROOF OF
AMPERE'S
CURRENTS
711
a
=
1,1.10-7,
which
agrees
very
well
with the theoretical
one
1,13.
10-7.
We
must
observe,
however,
that
we
cannot
assign
to
our
measu-
rements
a
greater precision
than of
10%.
It
seems
to
us
that within these limits
the
theoretical
conclusions
have been
fairly
confirmed
by
our
observations..
The
experiments
have
been
carried
out in
the
"Physikalisch-Tech-
nische
Reichsanstalt". We want
to
express
our
thanks
for
the
appa-
ratus
kindly
placed
at
our
disposition.
Physics.
-
"On
a
possible influence
of
the
Fresnel-coefficient on
solar
phenomena".
By
Prof. P.
Zeeman.
(Communicated
in the
meeting
of
September
25,
1915).
We
shall
prove
here,
that the
presence
of
the
term
l/m
of
Lorentz
in the
expression
for
the
Fresnel
coefficient
(cf.
also
my
paper
Vol. 18,
p.
398 of these
Proceedings) may
give
rise
to
a
change
in
the
propagation
of
lightwaves
if
in
a moving, refracting
medium
a
change
of
velocity occurs. I suppose
the
medium to
have
everywhere
the
same
density
and
to be
flowing
with
a
velocity v
parallel
to the axis
of
X
in
a
system
of
coordinates
that
is
at
rest with
respect
to
the observer.
In the
direction of
the
Z
axis
a
velocity
gradient
exists
in
such
a way,
that
the
velocity
decreases with the
distance to the
X axis and
becomes
zero
at the distance
z
-
A.
If
now
the
incident
lightbeam (with
a
plane
wave front)
is
parallel
to
the
axis
of
X, the
parts
of the
wave
fronts which
are
near
this
axis will be
more
carried
with
the medium than
those
at
a greater
distance.
The
wave
front will thus
be
rotated.
If the
velocity
decreases
linearly in
the
direction
of
the
Z
axis
the wavefront
will
remain
plane.
In
a
time
t
the
angle
of
rotation,
(supposed
to
be
small)
will
be
a
=
e.v.t/A,
where
b
is
the
Fresnel
coefficient
and
where
v
and
A
have the above
mentioned
meaning.
More in
general
we
may
consider
an
element of the
wave
front
and then
write
dv/dz
for
-.
Moreover
t
may
be
expressed as a
func-
tion
of
the
velocity
of
light
and
the
path
through
which
the
rays
have travelled,
so
that
we
find
si
dv
" =
.SS
(1)
46
Proceedings
Royal
Acad. Amsterdam.
Vol. XVIII.
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