DOC.
56
371
processes
is
known
(of
magnitude hv)
if the latter consists in the
absorption
or
emission
of
radiation of
a
specified
frequency.
Especially
interesting
would
be
the
study of exceptions to
Stokes'
law. [54]
In
order
to explain
these
exceptions,
one
has
to
assume
that
a
light
quantum
is emitted
only when
the emission
center
in
question
has
absorbed
two
light
quanta. The
frequency of such
an
event,
and
thus also the intensity of the
emitted light
having
a
smaller
wavelength
than the
producing one,
will in this
case
have to be proportional to
the
square
of
the
intensity
of
the
exciting
light
at weak
irradiation
(according
to
the
law
of
mass
action), while
according
to
Stokes' rule
a
proportionality
with the first
power
of the
exciting
light intensity is
to be expected at weak
irradiation.
[55]
b)
If the
absorption1
of each
light
quantum
brings
about
an
elementary
process
of
a
certain
kind, then
E/hv
is the
number
of these
elementary
pro-
cesses
if the
quantity of
energy E
of radiation
of
frequency
v
is
absorbed.
Thus,
for
example,
if the
quantity
E
of
radiation
of
frequency
v
is
absorbed
by
a
gas
being
ionized,
then it is
to
be
expected
that
gram
E/Nhv
molecules of the
gas
will
be
ionized. This relation
only
appears
to
presume
the
knowledge
of
N;
for if
Planck's radiation formula is written in the
form
o
1
p
=
av*
-
,
-
1
then
E/RBv
is the
number
of
gram-molecules
ionized.
This
relation, which I have
already presented
in
my
first
paper2
on
this
subject,
has
unfortunately remained unnoticed thus far.
[58]
c) The
results noted in
5
lead
to
a
modification
of
the kinetic
theory
of
specific
heat3
and to
certain relations
between
the
optical and
the thermal
behavior of bodies.
1Of
course,
the
analogous
consideration holds also
conversely
for the
produc-
tion of light
by
elementary
processes
(e.g.,
by
collisions
of ions).
2Ann. d.
Phys.
(4)17 (1905): 132-148,
§9.
3A.
Einstein,
Ann.
d.
Phys. (4)22
(1907): 180-190 and 800.
[56]
[57]
[59]