EARLY WORK ON
QUANTUM
HYPOTHESIS
135
tion,
and for the first time
publicly
linked
his work
on relativity
and
on
the
quantum
hy-
pothesis.
He demonstrated the fundamental
inability
of
classical mechanics and
Maxwell's
electrodynamics
to account for
a
number
of
phenomena
connected with
electromagnetic
radiation,
again
showed the
utility
of
the
quantum hypothesis
in efforts to
comprehend
the
structure
of
radiation,
and
speculated
about modifications
of
existing
theories
that
might
lead to
a
consistent
theory
of
radiation
explaining
the
quantum hypothesis.[6]
II
Einstein started to
study black-body
radiation well before 1905.
Mach's
Wärmelehre,
which Einstein read in
1897
or shortly
thereafter,
contains two
chapters on
thermal radia-
tion,
culminating
in
a
discussion
of Kirchhoff's
work.[7]
Kirchhoff
showed that the
energy
emission
spectrum
of
a perfectly
black
body
(defined
as one absorbing
all incident radia-
tion)
at
a given temperature
is
a
universal function
of
the
temperature
and
wave length.
He inferred that
equilibrium
thermal radiation in
a cavity
with walls maintained
at
a
certain
temperature
behaves like radiation emitted
by a
black
body
at the
same temperature.[8]
H. F.
Weber,
Einstein's
physics professor
at
the
ETH,
attempted
to determine the uni-
versal
black-body
radiation function. He made
measurements
of
the
energy spectrum
and
proposed an empirical
formula for the distribution function.[9] He showed
that,
as a con-
sequence
of
his
formula,
Xm
=
constant/T
(where
Xm
is
the
wavelength
at the
maximum
intensity
of
the
distribution),
thus
anticipating
Wien's
formulation
of
the
displacement
law
for
black-body
radiation.[10]
Weber described his work in
a course
at the ETH
given during
the winter semester
of
1898-1899, for which Einstein
registered.[11]
By
March
1899,
Einstein had started to think
seriously
about the
problem
of
radia-
tion.[12]
In the
spring
of
1901,
he
was closely following
Planck's
work
on
black-body
radiation.[13]
Originally,
Planck had
hoped
to
explain irreversibility by studying
electro–
[6]
For further discussion
of Einstein's
papers
on
the
quantum hypothesis, see
Hermann
1969;
Jammer
1966; Jungnickel
and
McCormmach
1986b,
chaps.
25-26; Klein
1977, 1979, 1980;
Kuhn
1978;
Mehra and
Rechenberg
1982;
and
Pais
1982.
[7]
See Mach
1896, pp. 124-152;
Kirchhoff's
work is discussed
on pp.
140-144. For
an
indi-
cation that Einstein
may
have read this work
around
1897,
see
Einstein to Mileva
Maric, 10
September
1899
(Vol.
1,
Doc.
54), note
8.
[8]
See
Kirchhoff
1860. For
surveys
of
re-
search
on black-body
radiation
up
to
and includ-
ing
Planck's
work,
see
Kangro 1976;
Kuhn
1978;
and
Pais
1982,
pp.
364-372.
[9]
See
Weber,
H. F.
1887, 1888.
For
a survey
of Weber's
work, see
Kangro
1976,
pp.
37-40.
[10]
Einstein used this result in
his first discus-
sion
of
black-body radiation,
Einstein 1904
(Doc. 5), pp.
360-362,
without
citing
a source.
Wien formulated the
displacement
law in Wien
1893,
which cites
Weber's
work
(see p. 62).
For
a history
of
the
displacement
law,
see
Kangro
1976,
chap.
3.
[11]
For the
contents
of
the
courses,
see
the
notes
of
Emil Teucher
on
"Prinzipien,
Apparate
und Messmethoden der
Elektrotechnik"
(SzZE
Bibliothek, Hs
32).
For
Einstein's
registration,
see
ETH Record and
Grade
Transcript (Vol.
1,
Doc.
28,
p.
47).
[12]
See Einstein
to
Mileva
Maric, 13
or
20
March,
1899
(Vol. 1,
Doc.
45).
[13]
See Einstein
to
Mileva
Maric,
4
April
1901
and
10
April
1901
(Vol. 1,
Docs. 96 and
97).
He had
evidently
read
some
of Planck's
pa-
pers on black-body radiation,
and
indicated his
intention
to read
Planck
1901a. It
is
possible
that
Einstein
had
already
read
Drude
1900c,
a