DOC.
25
SOLVAY
DISCUSSION REMARKS
401
In
§4
of his
lecture,
Sommerfeld
presented an explanation
of the
photoelectric
effect which he had
developed
in collaboration with
Debye
and earlier sketched in
a
lecture
(Sommerfeld 1911b),
in the discussion of which
Einstein had
participated; see Sommerfeld
et
al.
1911
(Doc. 24).
For
evidence of further
exchanges
between
Sommerfeld and Einstein
on
this
topic,
see
Sommerfeld 1914, p. 257.
Since Sommerfeld's
explanation is
based
on a resonance
effect between the incident radiation and
an atom,
the
photoelectric
effect
should, as
he
acknowledged
in his lecture
(see Sommerfeld 1914, p. 284; Sommerfeld
1912,
p. 355),
be
more susceptible
to
material
properties
such
as
the
damping
of
atomic oscillations
than
it should be
according
to
the
explanation
given
in Einstein 1905
(Vol.
2,
Doc.
14),
§8.
For
a
historical overview of alternative
explanations
of the
photoelectric effect, see
Stuewer 1970 and Wheaton
1978.
No. 242
(Sommerfeld
et
al.
1914,
p.
315;
Sommerfeld
et al.
1912,
p. 390)
[2]0)
According
to
Sommerfeld's
theory
of the
photoelectric effect,
the number of
electrons emitted
per
unit of
time
can
be
proportional
to
the
intensity
of
light only
if
one
totally
rules
out
a damping
of the
oscillatory
motion.
IX.
LANGEVIN
In his
lecture, Langevin
reviewed
the
kinetic
theory
of
magnetism
and in
particular
the work
of
Pierre Weiss.
Following a suggestion
made
earlier
by Gans, Langevin attempted,
in
the
last
part
of his
lecture,
to
use
Sommerfeld's
principle (see above)
in
a speculative
construction of
a
molecular model of
magnetization.
He
assumed
that
an
electron circulates around
a
center
that
attracts
it
by a
force characterized
by a power
law,
and
he obtained in this
way
a
rough agreement
with
experiment.
In
the
discussion
following
Weiss's
presentation
of
his theory
on an
earlier
occasion,
Gans mentioned
that
Einstein had
recently suggested to
him
an
explanation
of
the
units of
magnetism by quantizing
rotations
(see
Weiss 1911;
this has been noted in Kuhn
1978,
p. 312,
fn.
40).
In
a
letter written
to
Lorentz
soon
after the
Solvay meeting,
Einstein remarked:
"The
case
of electrons
in
a magnetic
field
already
mentioned in Brussels
is
interesting,
but
not
as
much
as
I thought
in
Brussels....
In
any
case,
the
thing
seems
to show
that
mechanics
already ceases
to
hold in
the
case
of the
electron
moving
in
a magnetic
field"
(Einstein
to
H. A.
Lorentz,
23 November
1911).
This discussion remark
is
transcribed from
Langevin
et
al.
1914, p.
328.
See also
Langevin
et
al.
1912,
p.
405.
A
manuscript
version does
not
exist.
It
would
be
interesting
to
apply
the
above calculation to
a
single
electron
in
the
magnetic
field.