xvi

INTRODUCTION

TO

VOLUME

6

consequences

of

the

theory,

and

wrote

a

major

review

paper

(Einstein

1916e

[Doc.

30])

as

well

as a

popular exposition

(Einstein

1917a

[Doc. 42]),

he

now

had time

once

again

to

pursue

other

interests,

returning,

in

particular, to

quantum theory.

His

two papers

on

the emission and

absorption

of radiation

in

quantum theory (Einstein 1916j

and Einstein 1916n

[Docs. 34

and

38])

represent

a

major step

forward in the

field.

Other features of this volume

are

the

papers resulting

from Einstein's col-

laboration with the Dutch

physicist

Wander Johannes

de

Haas

on

an

experi-

mental

investigation

of the existence of

Ampere's

molecular

currents,[3]

as

well

as

his first

appearance

as a

technical

expert

in

a

patent

dispute.[4]

The

volume concludes with

two appendixes:

the first

one

summarizes student

notes

for

two

lecture

courses

given by

Einstein

at

the

University

of Berlin

(in

1916/1917 and

1917/1918, respectively),

supplementing

his

own

lecture

notes

for

a course on

relativity

from

1914/1915,

which

are

presented

here

as

Doc.

6.

The second

appendix presents

notes

by an

auditor of

part

of

a

set

of

lectures

on relativity

given

by

Einstein

in

Göttingen

in

early summer

1915.

II

When Einstein left Zurich for Berlin in March

1914, general relativity

was

in

a

less than

satisfactory

state.

In

the

year

that

had

passed

since the

publication

of Einstein and Grossmann's

"Entwurf'

theory

(see

Einstein and Grossmann

1913

[Vol.

4,

Doc.

13]), not

much

progress

had been

made.

In

particular

the

lack of

general

covariance

was

still

a

problematic

feature

of the

theory.[5]

Al-

though

it

appears

that

Einstein

was by now

convinced of the

impossibility

and

even

undesirability

of

a

generally

covariant theory-his "hole

argument"

had been instrumental

in

this

respect[6]-it

was

still unclear

to

what

extent

the

theory

was

covariant. This

question

was

the

topic

of

a

final

collaborative ef-

fort of Einstein and Grossmann that led

to

the

publication

of Einstein and

Grossmann 1914b

(Doc.

2). Taking

a

Hamiltonian formalism of their

theory

as

a

starting point, they

tried

to

establish

more

precisely

than

in

their

previous

[3]See

the editorial

note,

"Einstein

on

Ampere's

Molecular

Currents,"

pp. 145-149,

for

more

information.

[4]See

sec.

IV

below.

[5]See

Vol.

4,

the editorial

note,

"Einstein

on

Gravitation and

Relativity:

The Collaboration

with Marcel

Grossmann,"

pp.

294-301,

for

a

detailed discussion of

the

developments

up

to

the

spring

of

1914.

[6]Put briefly,

the "hole

argument"

shows that

in

a

generally

covariant

theory

the metric field

is

not uniquely

determined

by

the

energy-momentum

tensor

of

matter. See,

e.g.,

Norton 1984

for

more

details.