DOC.
14
PROOF OF
AMPERE'S
CURRENTS
173
696
Physics.
-
"Experimental
proof
of
the
existence
of
Ampere's
molecular
currents."
By
Prof. A.
Einstein and
Dr.
W. J.
Dr.
Haas.
[1]
(Communicated by
Prof.
H.
A. Lorentz),
(Communicated
in the
meeting
of
April 23, 1915).
When it had
been
discovered
by
Oersted that
magnetic
actions
are
exerted not
only
by
permanent magnets,
but
also
by
electric
currents,
there seemed
to be
two
entirely
different
ways
in which
a
magnetic
field
can
be
produced.
This
conception,
however, could
hardly
be
considered
as satisfactory
and
physicists soon
tried
to
refer the two actions
to
one
and the
same cause.
Ampere
succeeded
in
doing
so by
his
celebrated
hypothesis
of
currents
circulating
around the
molecules
without
encountering any
resistance.
[2]
The
same
assumption
is
made
in
the
theory
of electrons
in the
[3]
form
e.g.
in
which it
has been
developed by
H.
A. Lorentz,
the
only
difference
being
that,
like electric
currents
in
general,
the
molecular currents
are now
regarded
as a
circulation of
elementary
charges
or
electrons.
It cannot be
denied that
these views call
forth
some
objections.
One
of these is
even more
serious than it
was
in
Ampere's
days;
it
is difficult to
conceive
a
circulation of
electricity
free
from all
resistance and therefore
continuing
for
ever. Indeed, according
to
Maxwell's
equations circulating
electrons
must lose
their
energy
by
radiation;
the molecules of
a
magnetic body
would
therefore
gradually
lose
their
magnetic
moment.
Nothing
of
the
kind
having
ever
been
observed,
the
hypothesis
seems
irreconcilable with
a
general
validity
of the
fundamental laws of
electromagnetism.
Again,
the law
of
Curie-Langevin
requires
that
the
magnetic
moment of
a
molecule
shall
be
independent
of the
temperature,
and
[4]
shall still
exist at
the absolute
zero.
The
energy
of
the
revolving
electrons would therefore
be
a
true
zero point energy.
In the
opinion
of
many physicists
however,
the
existence of
an energy
of
this
kind
is
very improbable. [5]
It
appears
by
these
remarks that after all
as
much
may
be said
in
favour of
Ampere's
hypothesis
as
against
it
and
that the
question
concerns important physical principles.
We
have
therefore
made
the
experiments
here
to be described,
by
which
we
have
been able
to
show that the
magnetic
moment
of
an
iron
molecule is
really
due
to
a
circulation of
electrons.
The
possibility
of
an
experimental
proof
lies
in
the
fact
that
every
negative
electron
circulating
in
a
closed
path
has
a
moment
of