662
DOC.
630
OCTOBER
1918
in somewhat closer
detail;
for
further
clarification in
this
regard
I
would also
like
to refer to
Annal, der
Phys.,
vol.
46,
p. 288,
where for
the
same
test
specimen
observed
successively
over
various distances
(:dropping distances:),
the
same
A2,
and therefore
the
same
mobilities,
resulted.[5]
With
respect
to
photophoresis, you yourself
note
that the
phenomenon’s
inde-
pendence
of
gas pressure
and the
unique
correlation between
the
velocity
of
fall,
color,
and
photophoretic
velocities
provide
the
best
proof
that the
observed
phe-
nomenon
is
not
disturbed
by gas
currents. The fact
that the
light ray
introduces
no
horizontal
motions in
the
gas
is
also
supported
by
the
existence of
optically
neutral
particles of
matter.
Recently,
we
succeeded
in
measuring
the
same
particle at
a
variety
of
gas
pressures, whereby
a
complete
constancy
of
the
light-positive or light-negative
forces,
and thus
independence
of
the
gas
pressure,
resulted.
Furthermore,
new
analyses
have
demonstrated
that
the
effect is
also
completely
independent
of
the
gas’s
chemical
properties.
Thus
the
photophoretic
energies
obtainable
from
the
following
tablet[6]
[Vide
6th
page.]
resulted for
light-negative
red selenium
particles
in
argon, nitrogen,
and
hydrogen.
(:If
gases
are seen as
atomistically
structured,
it also
seems
to
me very implausible
anyway
that the
closer
proximity
of
the
test
particle,
which is at most of
the
order of
magnitude
of the molecules’
mean
length
of path at low
degrees
of evacuation
but
is
already
much smaller
than the
mean
length
of
path,
should exert directed forces
on
the
test
specimen.:)
The
proofs
I
presented
seem
to
me
to have determined
unequivocally
that
a
direct
effect
of
the radiation
on
matter is
involved. As
concerns
the
motion of
the
plates,
this has
not
yet
been
analyzed
but
is
on
my program
for
the
immediate
future; only
after
performing
such
experiments
do
I
want
to
draw
the
relevant
conclusions.
Now like
you,
esteemed
colleague,
I
would
like to return
again
to
the
electron.
Regarding
the
system
of
hypotheses you
have
put
forward for
the
electron, up
to
now
I
only
went
so
far
as
to
say
that all
these
argumentations
contain
no
direct
charge
determinations
that
could conflict with
the
charge
determinations
for
the
single
test
specimen.[7]
Also,
the
entire
system
contains
no
proof
against
individ-
ual test
specimens, as
they
are
encountered at
measurement, having
arbitrarily
small
charges.
Once
one
has clarified
the
existence of such
small
charges,
the
question
of whence these
grouped charges
come
will
have to be raised in
the
fu-
ture,
provided
that
grouped charges are
thought
to
have been identified in various
phenomena
in nature.
Incidentally, your proposed
theoretical
arguments
against
the
relevant
theory
are
eliminated,
since in order to
maintain
e
and
h,
Maxwell’s
electrodynamics
would
have to be
abandoned,
without
being
able to
replace
them
yet
with
new
ones.