DOC. 28 SIMPLE EXPERIMENT
139
ohmic resistance
(in
order
to
avoid electrical
oscillations).
The
turning
of
the
commutator
charges
the
capacitor
in
reverse,
during
which time
a
field of short
duration is induced in the coil E, which in turn
reverses
the remanent
magnetism
of
the rod
S.
Further
required
is
an
arrangement
to
compensate
for the
geomagnetic
field,
e.g., a horizontally
movable
magnetic
rod at about the
height
of
the mirror.
The
experiment
is conducted in the
following
manner. First,
one
has to
compensate
for the earth's
magnetic
field
to
a degree
that the
resting
position
of
the
tiny
rod is
exactly
the
same
in both directions of
magnetization. (The reason
why
this
is
not
initially
the
case
is caused
by
the fact that the
poles
of
the rod
are
never
completely on
its
axis
of
rotation,
whereupon
the field of the earth
produces,
in
general,
an angular
momentum that has to be removed with the utmost
care.)
Next,
one
brings
a
small
magnet temporarily
close in order to induce torsional
oscillations
that
can
be
easily
followed with the
eyes
since the
light-pointer
is
set
up [p.
175]
with oscillation
periods
of
1
to 2 seconds. Now
one can begin
to
reverse
the
commutator
whenever the
light-pointer passes through
its
resting position,
which
means
the
tiny
rod receives
an
angular
momentum,
by
the effect to be
demonstrated,
whenever
its
angular
velocity
is
at
a
maximum. One achieves in this
manner an easily
noticeable
amplification, resp.
attenuation
of
the oscillations.
It
is
also
easily
demonstrated that
sign
and order
of
magnitude
of the
effect
comply
with
theory.
Attention must also be drawn
to
the
following points.
It
is
important
that the
point
of
suspension
of
the
tiny
rod is
as
precise as possible
in line with the
major
axis
of
inertia
(smallest
momentum of
inertia).
If
this is
not
the
case
with
good
approximation,
the horizontal deviations of the location of the
apparatus
will
give
cause
to initiate torsional oscillations
of
the
tiny
rod;
but
if
the
centering
is
a
good
one,
the
experiment can
be done well without
special suspension
of
the whole
apparatus (to
avoid vibrations of
it); e.g., one can place
it
on a
wall console.
The
poorer
the
centering
of
the
tiny rod,
the
more
sensitive is the
apparatus
to
variations
in
the
earth's
field,
and the
more
difficult it is also
to
compensate
the
earth's field
sufficiently.
There
were originally
considerable difficulties with the centric
suspension
of
the
tiny
rod,
but Herr
Jaeger
kindly
assisted
me
in
overcoming
them.
Finally,
the
[3]
following
almost droll method achieved the
goal.
The
tiny
rod is
fastened
Fig.
2.
vertically (and loosely!)
to
a
stand such that the end that is
to
be
suspended points
downward. The
copper spindle
with the threat of
quartz
is
suitably supported,
also
upside
down,
vertically
underneath the cork.
Hereby,
the
height
is to be
carefully adjusted
such that the
quartz
thread
(held by
the moistened
fingers
and directed
straight up)
just
does not
touch the
plane endpoint
of
the
tiny
rod
(see
sketch in
fig.
2).
The end
of
S
is
now
heated with the
very
small flame
of
a
gas
burner
(made
from
a
tapered glass pipe)
until
a
droplet
of
colophony
sticks
to
the
tiny
rod
S
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