THEORY OF RELATIVITY 273

indem

ich-soweit

es

anging-jene Annahmen einzeln einführte und

der

Reihe

nach ihre

Konsequenzen

verfolgte.[132]

The review

covers

relativistic

kinematics,

optics,

electromagnetic

theory,

the

relativistic

dynamics

of

a particle,

and the relativistic

dynamics

and

thermodynamics

of

an

extended

system.

He summarized the results

of

a

number

of his earlier

papers

on

the

theory

of

relativity,

sometimes

simplifying

his earlier

proofs.

He

adopted

Planck's

approach

to rel-

ativistic

dynamics

and

thermodynamics, although

often

giving

his

own proofs

of Planck's

results.[133]

In his

Salzburg

lecture,

Einstein reviewed the historical

background

of

the

theory

of

relativity

in

order to stress

some consequences

of

the

theory

for the

problem

of

the struc-

ture

of

the radiation

field.[134]

By discarding

the

concept

of

the ether and

by showing light

consists

of "structures"

("Gebilde")

that

carry

inertial

mass

from

an

emitter to

an

ab-

sorber,

he stressed

that the

theory

of

relativity opens

the

way

for

a

theory

of

light

that

includes both

corpuscular

and

undulatory

features. He went

on

to

argue

the

necessity

of

such

a

theory.

For further discussion

of

the

Salzburg

lecture,

see

the

Introduction,

pp.

xvii-xviii, and the editorial

note,

"Einstein's

Early

Work

on

the

Quantum Hypothesis,"

pp.

147-148.

Einstein wrote three

additional reviews

of

relativity

between 1910 and

1912.[135]

Ein-

stein 1910a and Einstein

1911e, written for

nonspecialized physics

audiences,

discuss

historical and foundational

questions.

The

technically

most detailed

of

all his

reviews

is

an unpublished manuscript

written about

1912.[136]

After

1912,

Einstein's

active

research

interests

no longer

included what

soon came

to be known

as

the

special theory

of

relativity.

He

occasionally

wrote

pedagogical

articles

on aspects

of

the

special

theory,[137]

and

con-

tinued to include reviews

of

the

subject

in

many expositions

of

the

theory

of

relativity as

a

whole.[138]

VI

The 1907 review concludes with

Einstein's

first

published

discussion

of

gravitation.

The

final

section,

entitled "Principle

of

Relativity

and

Gravitation"

("Relativitätsprinzip

und

Gravitation"),[139]

takes the

equality

of

gravitational

and inertial

mass as

its

starting

[132]

Einstein to Johannes

Stark,

1

November

1907.

[133]

Although

Einstein did

not

publish any-

thing

further

on

relativistic

thermodynamics,

it

appears

that later in his life he had doubts about

the

validity

of Planck's

approach

(see, e.g.,

Ein-

stein

to

Max

von

Laue,

29

January

1952).

[134]

See

Einstein

1909c

(Doc. 60),

pp.

482-

490.

[135]

After

1912,

Einstein's

reviews

of

relativ-

ity

include discussions

of

the generalized

theory,

with

primary emphasis on

the

problem

of

gravi-

tation.

[136]

The untitled

manuscript was

written in

1912

for Marx

1924,

publication

of

which

was

delayed

due

to the First World War

(see

Erich

Marx

to Einstein, 2

January

1922,

and Ein-

stein's

undated

reply

to

Marx's

letter

of

3

March

1922).

See Vol. 4 for this

manuscript.

[137] See,

e.g., Einstein 1935.

[138]

See

Einstein

1917a,

Einstein

1921b,

for

early examples.

[139]

See Einstein

1907j

(Doc.

47),

§

V,

pp.

454-462.