DOC. 60
CONSTITUTION
OF RADIATION 583
metal. For
a
discussion
of
contemporary
criti-
cisms
of
the
triggering hypothesis, see
Wheaton
1978a,
pp.
146-150.
[20]
See
Stark
1909a,
p.
583;
and
Stark's
com-
ment
on
this
paper,
in Einstein
et
al. 1909c
(Doc.
61),
p.
826.
[21]
Einstein's
conclusion
is
similar to
Stark's
assumption
that
light quanta are
endowed with
both
energy
and
momentum (see
Stark
1909c).
Stark's
paper
was
received
on
16
November
1909,
after Einstein's
lecture. Einstein dis-
cussed the directed emission of
light quanta
in
Einstein
to
Arnold
Sommerfeld, 19
January
1910. He later elaborated
on
the idea in Einstein
1916b.
[22]
For details
of Planck's
theory
of thermal
radiation
and the derivation
of
his
formula, see
Planck
1900a, 1900e,
and 1906c.
[23]
For
Einstein's
critique
of Planck's
theory,
see
Einstein 1905i
(Doc.
14),
Einstein 1906d
(Doc. 34),
Einstein 1907a
(Doc. 38),
and Ein-
stein 1909b
(Doc. 56).
[24]
This
figure can
be
calculated
from
the for-
mula for
Ev/e
in
Einstein 1906d
(Doc. 34),
p.
203.
[25]
See Rutherford
and
Geiger
1908
(German
translation, Rutherford
and
Geiger
1909),
which
gives
the
charge
of
an
a-particle (2e)
as
9.3
x
10-10
electrostatic units
(pp.
168, 173).
For
Regener's
result, see
Regener
1909, p.
965.
[26]
Planck
1901b,
p. 566;
Planck
1906c,
p.
163.
[27]
See
Einstein 1905i
(Doc. 14).
[28]
For further details of the
following argu-
ment, see
Einstein
1909b
(Doc.
56),
pp.
189-
190.
[29]
In
Planck
1910,
Planck criticized Ein-
stein's
interpretation
of the
expression
for
A2.
In
particular,
he did not
agree
with
Einstein's
inter-
pretation
of
the first
term.
For
Einstein's
re-
sponse, see
"Antwort
auf
Planks Manuskript,"
ca.
January
1910.
[30]
For
an
earlier
discussion
of
the
following
implications
of
the
momentum
fluctuation for-
mula,
see
Einstein 1909b
(Doc. 56),
pp.
190-
191.
[31]
See also Einstein
to
Hendrik
Lorentz,
23
May
1909. He
may
have had this idea when he
wrote Arnold Sommerfeld
on
19
January
1910
that
"the
localization which
we give
the electro-
magnetic energy
in
Maxwell's
theory
is
entirely
arbitrary;
but
so
far
this
conception
has
helped
me
little
in
clarifying
the
question" ("die
Lo-
kalisation,
welche
wir der
elektromagnetischen
Energie
in
der Maxwell'schen
Theorie
geben,
[ist]
eine
ganz willkürliche;
bis jetzt hat
mir
diese Erkenntnis aber
zur Aufklärung
der
Frage
wenig
genützt").
[32]
See also
Einstein's
comment
in
Einstein et
al. 1909c
(Doc. 61), p.
826.