202
DOCS.
281,
282 SEPTEMBER
1911
are
quite
daring.
If
only we
had
a truly
larger planet
than
Jupiter![5]
But
Nature
did not
deem
it
her
business
to
make the
discovery
of
her
laws
easy
for
us.
I
have
already
been
told
by
the
astronomer at
our
local
observatory
that
such
photographs
had been made
in
Hamburg.[6]
It will be
very
interesting to
see
what
you
will find
out
when
you measure
the
plates.[7]
I
beg
of
you
to
tell
me
then the results of
your investigation.
With
collegial greetings, yours very truly,
A.
Einstein
282.
From Michele
Besso
[Gorizia,
before
11
September
1911][1]
near
absolute
zero:
could
one
not
conjecture
that
the
lengths
of
the
stay
would
depend
on
the
speed
of
the
thermal motion-down
to
very low,
hitherto unattained
temperatures,
but that
the most
probable
direction
in which
the electron
leaves
the
state
of
rest would be determined
by
the effective electric force? It
seems
to
me
that
in this
way
one
obtains the linear
dependence
of
the
resistance
on
the admixture, in contrast
to
that
form
of the
theory
in
which the
electrons
are
conceived
as
being
under the
influence
of the electric
force
only
during
their
free
flight.
I
have done
much
thinking
about
the
electron
theory
of metals
since
then. Your
result
for
low-concentration
alloys,
namely,
that
the
resistance
must be
proportional
to
the
square
of the concentration of
the
admixture,
could be
circumvented,
it
seems
to
me,
if
one
assumed that
it
is
precisely
the
inhomogeneities
that
are
the
sources
of
electrons;
this
might
be
assumed
for
metals
as
well,
since it
is
not
at
all absurd to
assume
that
it
is
precisely
the
dissociated
atoms
that
act
as
the
stumbling-blocks.
But
then
one
would
again get
a
resistance
proportional to
n
instead of
to
T
(since we
would
have
n
=
k-^).[2]A
Besides,
even
in the
case
of low-concentration
alloys,
one
still has
to put
up
with the
disagreeable
u
at
absolute
zero.
-
-
Another
argument,
one
based
on
the
quantum
of
action,
seems
to
me
to
lead
to
the actual
relationship
with
A,
namely,
the
following.
Consider
a
group
of
planes
that
are
perpendicular
to
the direction of
the
electric
force and
separated
from
each other
by
the
distance
X,
so
that each
time
an
electron reaches
such
a
plane,
its
velocity
is
independent
of the
previous
one.
I
take
all the velocities to be
parallel to
the direction
of
the
electric
force. In
this
way,
too,
one
obtains Drude's
formula[3]
(which
is
also
obtained,
even more intuitively,
if the
planes
are
taken
parallel
to
the electric
force)
if
one
bases
oneself
on
conventional
mechanics. But
if,
instead of
applying
mechanics,
one
assumes
that
no
other
energy
quantities
occur save
those that
correspond to quanta,
and