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