EINSTEIN
ON
AMPÈRE'S
MOLECULAR CURRENTS
I
Einstein's four
papers
and two notes
on Ampère's
molecular
currents,
three of which
were
written
in collaboration with the Dutch
physicist
Wander Johannes
de Haas,
oc-
cupy
a
special place among
Einstein's
publications. They
deal with
a
topic only
in-
directly
connected with
any
of his
contemporary
or
later
interests; in addition,
they
report
on
experimental
work done
by
Einstein
(together
with
De Haas)
and
are
in
this
respect exceptional
as
well.[1]
The
first
paper,
Einstein and De Haas 1915a
(Doc.
13), was
presented
on
19
Feb-
ruary
1915
as a
lecture
to
the Deutsche
Physikalische
Gesellschaft
in
Berlin,
and sub-
sequently
was
published
in
revised and
expanded
form.
A
week after the
publication
of the first
paper
a
shorter version
appeared,
Einstein 1915c
(Doc.
15),
without cal-
culations and with
only
a
short reference
to
the
measurements,
but with
more
details
on
background
and motives. After
De
Haas had returned
to
the Netherlands
in the
spring
of
1915,
a
second
joint paper
with Einstein
was
submitted
to
the
Amsterdam
Academy
of Sciences
by
De Haas's
father-in-law, H.
A.
Lorentz.
It
was
first
pub-
lished
in
Dutch
(Einstein
and de Haas
1915b)
and
then,
as was
customary,
in
English
translation
(Einstein
and
de
Haas
1915c).
It is the
latter version that
is
presented
here
as
Doc.
14.
Almost
simultaneously
and
prompted by
Lorentz's
discovery
of
a
calcu-
lational
error,
Einstein
published
Einstein 1915d
(Doc.
16),
a
correction
to
the earlier
papers.
Information
on
earlier similar
experiments
by
the American
physicist
Samuel
Barnett,
unknown
to the authors
when
they
wrote their
first
paper,
was
acknowledged
in the fall of
1915
in
the form of the brief
note,
Einstein and De Haas 1915d
(Doc.
23).
A
year
after the first
experiments,
Einstein
published
a
final
paper,
Einstein
1916d
(Doc. 28),
reporting
on a
modified
experimental arrangement
and
on
the
mea-
surements performed
with
it.
II
Immediately
after Orsted had discovered the effect of
an
electric
current
on a
magnet
in
1820, Ampère
showed that
two
electric circuits
exert
a
magnetic
force
on
each oth-
er.
The results of
subsequent experiments
led him
to
the
hypothesis
that
magnetism
is
an
electrical
phenomenon
caused
by
small closed electrical
currents
perpetually
flowing
in
hypothetical "magnetic
molecules."
Starting
with Maxwell in the
second
half of the nineteenth
century,
a
number of scientists undertook
experiments
to
test
Ampère's hypothesis.
Those
tests
were
based
on
the idea that if
any
kind of
mass
transfer
was
involved in the
microscopic
currents,
e.g.,
because the
currents
were
due
[1]See
Galison
1987,
chap. 2,
for
a
detailed historical discussion and
an
analysis
of
the work
by
Einstein and De Haas
on
Ampère's currents.
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