DOC.
5
LOCALIZATION OF ELECTROMAGNETIC ENERGY
207
Doc.
5
On the
Theory
of
Light
Quanta
and the
Question
of
the Localization
of
Electromagnetic
Energy
by
A.
Einstein
[Archives
des
sciences
physiques
et
naturelles 29
(1910): 525-528]
What
we
understand
by
the
"theory
of
light
quanta"
may
be
formulated
in
the
following
fashion:
a
radiation of
frequency
v
can
be
emitted
or
absorbed
only
in
a
well-defined
quantum
of
magnitude hv1 (and
not in
a
smaller
quantum).
With the
aid
of
this
theory,
several
groups
of hitherto
unexplained
phenomena
can
be considered
from
one
and the
same
point
of
view. This
is
true
of Stokes's
law
of
phosphorescence
and
the
principal
laws
for the
emission
of cathode radiation
produced
by
visible
and ultraviolet
light (as
well
as by
X
rays).
As
a
matter
of
fact,
the
kinetic
energy
L
of
photoelectri-
[2]
cally
produced
cathode radiation increases
proportionally-or
at
least
approximately
proportionally-to
the
frequency
of the
exciting light according
to
the formula
L
=
c +
hv,
where
c
is
a negative
constant
that
depends on
the
nature
of
the
body
under
consideration. In
general,
it
can
be
said
that the
theory
of
light
quanta
is
the
quantitative
expression
of the
experimental
fact
that the
energy
of the molecular
phenomena
produced
by light
increases
with
the
refrangibility
of the
light employed.
[3]
It
is
now
generally
accepted
that molecular
mechanics,
with
the
aid
of the
Maxwell-Lorentz
equations,
leads to
the radiation formula
p
=
Kv2T,
as
it has
been
demonstrated
in
particular
by
Mssrs.
Jeans
and
H. A.
Lorentz.
This
formula
is
[4]
contradicted
by
experiment
and
does not
contain the
constant h: this leads to
the
conclusion
that the foundations of the
theory
must
be modified
in such
a way
that the
constant
h
will
play a
role
in it.
Only
in this
way
will it be
possible
to establish
a
theory
of radiation and
to
understand the fundamental
laws
of radiation
cited above. This
modification
of the foundations
has not
yet
been
possible
to
accomplish.
The
theoreticians
have not
yet
even come
to
an agreement
in
regard
to
the
following
question:
Can the
light
quanta
be
accounted for
entirely
by a
characteristic
of the
emitting
or
absorbing substance, or
should the
electromagnetic
radiation itself be
assigned,
besides
a wave
structure,
a
second kind of
structure,
such
that the
energy
of the
radiation itself
is already
divided in definite
quanta?
I believe
that
I have
proven
that
[5]
hv
1
h
is
a
universal constant
that
enters
the radiation
equations
of
Wien
p
=
hv2e
and
Planck
\
1
p
=/iv3
hv
W
-
l
[1]