CONSTITUTION
OF
RADIATION 386
before the emission, and
M1
its
mass
after the
emission,
then
one can
put,
neglecting terms
of
higher
than the
second
power,
1/2
M0v2
=
1|2
M1v2
+
2 -^v2
or
M0
=
M1
+
.
Thus
the inertial
mass
of
a body
decreases
upon
emission
of
light.
The
energy
emitted
must
be reckoned
as
part of
the
body's
mass.
From
this it
can
be
concluded further that
each absorption
or
release of
energy
brings
about,
respectively,
an
increase
or
decrease of the
mass
of the
body
involved.
Energy
and
mass
appear
as
equivalent
quantities
the
same
way
that heat
and
mechanical
energy
do.
The theory
of
relativity
has
thus
changed
our
views
on
the
nature
of
light insofar
as
it
does not
conceive
of light
as
a
sequence
of states of
a
hypothetical
medium,
but
rather
as something
having
an
independent
existence
just like
matter.
Furthermore,
this
theory
shares
with the
corpuscular
theory
of
light the characteristic feature
of
a
transfer
of
inertial
mass
from the
emitting to
the
absorbing
body. Regarding
our
conception
of the
structure of
light, in particular
of
the distribution
of
energy
in the irradiated
space,
the
theory
of
relativity did
not
change
anything.
It is nevertheless
my
opinion
that with respect
to
this
aspect of
the
problem
we
are
at
the
threshold
of
not
yet
fully foreseeable,
but nevertheless
highly
significant,
developments.
What
I
shall presently
say
is for the
most
part
my
private
opinion
or,
rather, the result
of
considerations that
have not
yet
been
sufficiently
checked
by
others. If
I
nevertheless present these consid-
erations, this should
not be
attributed
to
excessive confidence in
my
own
views
but rather
to
the
hope
that
I
may
induce
one or
another
among you
to
concern
himself with the
problems
in
question.
Even
without getting
deeper
into
any
theoretical
consideration,
one
can
notice that
our
theory of light cannot explain
certain fundamental properties
[17]
of
light
phenomena.
Why
does it
depend
only
on
the
color,
but
not
on
the
intensity, of light
whether
a
given
photochemical
reaction
will
or
will
not
occur?
Why
are
short-wave
rays
in
general chemically
more
effective than
long-wave
ones?
Why
is the
velocity of photoelectrically
produced
cathode