338
DOCS.
349,
350
JUNE
1917
Einstein discusses
Felix
Ehrenhaft’s
theory
of
“subelectrons,”
providing
equations
for
its
testing.
The last
section
is
devoted to
the
question
of
the
compatibility
with
the
wave
theory
of
directed
momentum
transfer:
...
Although Pointing’s
theory
of momentum
is
compatible
with
Maxwell’s
equations,
it
is
not
a
consequence
of them. Our
inability
until
now
to
discover
a
detailed
energy-momentum
localization
analogous
to
quanta,
should not imme-
diately
lead to
the
interpretation
that
it
is
an impossibility
...
350. To
Paul
Ehrenfest
[Berlin,]
3
June
1917
Dear
Ehrenfest,
I
am
corresponding quite busily
with Adler
because
he
has written
something
about
relativity theory
that
is
unfortunately
only very flimsily supported.[1]
But
otherwise,
he
is
a
terrific
fellow.
It
would
be
best
to
send
offprints
to
his
wife
(Mrs.
Adler,
junior,
for Dr. Fritz
Adler,
1
Blumel
Alley,
Vienna
VI).
I
optimistically
hope
that
nothing
will
happen
to him.
He
has
the
sympathy
of
all discrimi-
nating
persons,
also here
more
than
would be
expected.
Slowly
but
surely,
a
change
is
generally
taking place
toward
a
moderate
and
natural
mentality.
But
a
tremendous
amount
of fertilizer
is
needed before
the little
plant
can grow!
The
generalization
by
Sommerfeld
is
as
follows.[2]
Let
there
be
a
problem
in
which
as
many integrals
L(qv, pv)
=
const
exist
as
degrees
of
freedom. Then
the
momenta
pv
can
be
expressed
as (multiple)
functions of
qv.
On
the other
hand,
the
path’s
curve
fills
a
certain
portion
of
the
qv-space entirely,
so
that it
comes
arbitrarily close to
every
point
in it.
Then the
system’s
path
in
the
qv-space
generates
a
vector field
for
the
pv’s.
In
a
“Riemann
foliated”
qv-space,
the
pv’s
can
be
interpreted
as
unique
and
always
constant
functions of
the
qv’s.
Now
we
regard
the
sum
da
=
Y^Vudqv,
V
formed for
a
random line element
of
the
qv-space.
This
sum
is
invariant
under
coordinate transformations and
is
in
addition
a
complete differential.
The latter
can
be inferred from
Jacobi’s
law.
The
integral
fda
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