184
DOC.
14
PROOF OF
AMPERE'S
CURRENTS
707
had been
made
in
the
application
of
the
method, so
that
we
must
[14]
consider
as a
failure
this
part
of
our investigation.
The
negative
sign
of the
circulating
electrons is
however
made
very
probable
by
the
agreement
between the
magnitude
of the
observed
effect
and
the value
we
have deduced
for it
from
that of the ratio
e/m
for
negative
electrons.
§
7.
More accurate measurements.
The
measurements
thus far
described
furnished
a satisfactory con-
firmation
of the
theory,
but
were
much
lacking
in
precision.
The
field
in
the
coil
was
too
weak
practically to
cause
the sudden
reversals of the
magnetisation
assumed
in the
theory.
Further the
coefficient
of
damping
x
could not
be
determined
with
any
accuracy.
Even
the
question may
arise whether the
influence
of the
damping
is
represented rightly
by
the
term
Pn
in
equation
(6).
For these
reasons
we
have somewhat
modified
our apparatus.
In
order
to
quicken
the
reversals
of the
magnetisation
we
used
instead
of the former short
coil
one
of
62
cm length (about
100
windings
to
a
cm)
the
amplitude
of whose
field,
for
an
effective
strength
of
1,45
Ampere was
260 Gauss in its central
part
and
therefore 130
Gauss at
the ends. In order
to
diminish the
demagnetizing
influence
of
the
poles we
further
used
a
cylinder
of
16
cm length
and
0,17
cm
diameter. The mirror
was now
suspended
by a
thin walled tube that
was
sealed to
the lower end of the
iron
cylinder.
It
just
projected
beneath
the lower end of
the
coil.
In order
to
avoid
a
determination of the
coefficient
of
damping
and
assumptions
about the law of
damping
a
series
of
experiments
were
made
in
which,
for
a
definite
length
of the
wire,
the
amplitude |a|
was
determined for
different
frequen-
cies
of the
alternating current,
so
that
a
"resonance curve"
could
be
drawn.
The
alternating current
was
furnished
by a
generator
placed
in
the cellar of the
building
and
moved
by
the
current of
a
battery
of
storage
cells.
The
apparatus
in the
working room
comprised a
variable resistance connected
in parallel to
the
windings
of the
field
magnets.
By
varying
this
resistance
we
could
change
within certain
limits
the
exciting
current in the
motor
and
therefore the number
of its revolutions and the
frequency
of
the
induced
alternating
current. The
current
which
passed
through
the
variable resistance
was
controlled
by
an amperemeter.
When
all
other
things were kept
constant the
frequency
of the
alternating
current
was a
function
of