236

DOCUMENT 179 JANUARY

1916

[1]See

Doc. 158.

[2]Because

of

the

frequent closing

of

the

border between

Germany

and

Switzerland

(see

Doc.

170).

[3]Wedding

plans were

traceable

to

Elsa

Einstein’s

parents,

Rudolf

and

Fanny

Einstein

(see

Doc.

152).

[4]The

projected

book

appeared as

Einstein

1917a

(Vol.

6,

Doc.

42).

[5]

An

example

of

a

misleading

popularization

was

provided by

Max Weinstein in the

pages

of

the

Berliner

Tageblatt

at

the

end

of

the

following

month

(see

Doc.

204).

[6]In

1908,

Einstein had

criticized

Hermann

Minkowski’s four-dimensional

approach

to

special

relativity as

placing

“rather

great

demands”

(“ziemlich

grosse

Anforderungen”) on

the

reader, though

two

years

later

his

appreciation

of

the mathematical

formalism

had

grown (see

Jakob Laub

to

Einstein, 18

May

1908

[Vol.

5,

Doc.

101], note 12),

and in his 1912 manuscript

on

the

special theory

of

relativity

(Vol. 4,

Doc.

1),

he

incorporated

it.

[7]Beginning

in the

summer

of

1913,

Einstein

and

Besso had collaborated

on a

calculation

of

the

perihelion

shift

of

Mercury

in the framework

of

the “Entwurf”

theory.

See Doc.

153,

note

4,

for

more

details.

[8]See

Docs. 162 and 168 for similar remarks

made

by

Einstein the

preceding

month.

[9]In

their

joint

work

on

the

perihelion

shift,

Einstein

and Besso had also

calculated

the effect

of

the sun’s rotation

on

the

perihelion

motion

of

Mercury (see

Vol. 4,

Doc.

14,

especially

[pp.

18-22],

[p.

32],

and

[pp.

34-35]).

Besso had

subsequently

added calculations

dealing

with the effect

of

the

rotation

of

the

sun

and

of

Jupiter on

the motion

of

the nodes

of

Mercury,

Venus,

and Mars

(see

Vol.

4,

Doc.

14,

[pp.

45-50]

and

[pp.

41-42]).

[10]See

Doc.

43,

note

2,

and Doc.

173,

note

3,

for

more on

the role

of

the “hole

argument”

in the

development

of

general relativity.

[11]This argument

was

first formulated

in Doc.

173.

[12]The

papers are

Einstein

1915f

and 1915g (Vol. 6,

Docs.

21

and

22);

Tis the

trace

of

the

energy-

momentum tensor

of

matter. See Doc.

139,

note

2,

for

more on

the

postulate.

[13]See

Einstein 1915i

(Vol. 6,

Doc.

25),

where

the

condition T

=

0 is abandoned.

[14]The

condition T

=

0 would have

suggested

that matter is

electromagnetic

in nature

(see

Ein-

stein

1915g [Vol.

6,

Doc.

22]).

See Einstein 1909b

(Vol. 2,

Doc.

56),

sec. 10,

for

the dimensional

con-

sideration

to

which

Einstein

alludes;

see

also

Einstein

to H. A.

Lorentz,

30

March

1909 and 23

May

1909

(Vol.

5,

Docs. 146 and

163),

and H. A.

Lorentz

to

Einstein,

6

May

1909

(Vol. 5,

Doc.

153),

for

a

discussion

of

this

point.

[15]Major

German

military successes

in the fall

of

1915 in the East had

dimmed

the

prospects

for

peace.

179. To

Paul Ehrenfest

[Berlin,]

3.1.

16

Lieber Ehrenfest!

Meine Anworten

zu

Deinen

Bemerkungen

bedürfen noch

einer

Ergänzung.[1]

Es

wäre nämlich

denkbar,

dass Deine

vier

Relationen

(IV)

den

Feldgleichungen

wi-

dersprächen,

d.

h.

nicht

mit Ihnen

vereinbar

wären. Deshalb ist

es

doch

von

Inter-

esse zu

sehen,

dass Deine vier

Gleichungen

identisch erfüllt sind. Dies sieht

man

im

Anschluss

an

meine

Entwicklungen

in den Arbeiten wie

folgt

am

leichtesten

ein.

(Beim

Zitieren ist

die Arbeit

"Zur

allg.

Rel. Theorie“ mit

A,

die Arb.

"Die

Feldgl.

d.

Gravitation“ mit

B

bezeichnet.[2]

Wenn

man

statt

(7)B

die

Gleichung[3]