EINSTEIN

ON THE

STATIC

FIELD

127

be the

only

serious alternative

to his

tensorial

theory

of

gravitation

and

to

whose

development

he

significantly

contributed.[39]

Even

though

the

polemic

between Einstein

and

Abraham

in 1912

was

at

times rather

heated,

Einstein continued

to

respect

Abraham

as a

lucid critic of

his

work

on

grav-

itation.

In

his

papers

as

well

as

in his

correspondence,

Einstein

expressed

himself

in

no

uncertain

terms

about Abraham's rival

theory

but

he

always

made

it

clear that he

admired Abraham

as a

capable

physicist.[40]

Einstein retained

this

opinion

even

after

a

second

controversy

with Abraham

on

the

theory

of

gravitation

arose

two

years

later.[41]

IV

When Einstein

began

to consider

the

dynamic gravitational field

in

early

1912,[42]

he

proceeded systematically

from the

special

to

the

more general,[43]

convinced that

arti-

ficial

hypotheses were

to

be

avoided.[44] He

compared

his

earlier

treatment

of

the

static

gravitational

field to

electrostatics,

and he

was aware

that

this

static

theory

did

not

yet

include the

analogon

to

magnetostatics,

that

is,

it

did

not

cover

the

case

of

a stationary

gravitational

field

caused

by moving

masses

such

as

those of

a

rotating

ring.[45]

Ein-

stein 1912e

(Doc. 7)

gives

evidence of

one

of the

first

steps

which Einstein took

beyond

statics,

following

the

analogy

of

electrodynamics.

In this

paper

he

analyzes

a

physical system consisting

of

a

point

mass

inside

a

massive hollow

shell in

order

to

investigate

the effect of

an

acceleration of the

shell

on

the

mass

inside. Einstein

describes

this

effect

as an

analogon

of

electrodynamical

induction. The

paper

illus-

trates

the crucial influence of Mach's

critique

of Newton's mechanics

at

the

beginning

of Einstein's search for

a

general theory

of

relativity.

In his

simple

model Einstein

is

in

fact able

to

show that what

he

defined

to be

the inertial

mass

of the

point particle

is

increased

by

the

presence

of the massive

shell,

which

is

what

he

expected

on

the

basis of his

reading

of Mach's

critique

of Newton's

concept

of

inertia.[46]

[39]For

further

discussion,

see

the editorial

note,

"Einstein

on

Gravitation and

Relativity:

The

Collaboration with Marcel

Grossmann,"

pp.

298-300.

[40]Various remarks

on

Abraham's

quality

as a

physicist

and

on

his character

are

found

in

Einstein's

correspondence

(see,

e.g.,

Einstein

to

Jakob

Laub,

16

March

1910

[Vol. 5,

Doc.

199];

Einstein

to

Michele

Besso, 26

March

1912

and after

1

January

1914

[Vol. 5,

Docs. 377

and

499];

and Einstein

to

Alfred

Kleiner,

3

April

1912

[Vol. 5,

Doc. 381]).

[41]See

Abraham

1914a, 1914b,

and Einstein 1914h

(Doc. 31),

and

for evidence of Einstein's

estimation,

Einstein

to

Michele

Besso,

after

1

January

1914

(Vol.

5,

Doc.

499).

[42]See

Einstein

to

Wilhelm

Wien, 24

February

1912

(Vol.

5,

Doc.

365),

and

also

Einstein

to

Wilhelm Wien,

11

March

1912

(Vol.

5,

Doc.

371).

Serious work

on

the

dynamic

case only

began

at

the end of March

(see

Einstein

to

Michele

Besso, 26

March

1912

[Vol. 5,

Doc.

377]).

[43]See

Einstein

to

Paul

Ehrenfest,

10

March

1912

(Vol.

5,

Doc.

369).

[44]See

Einstein

to

Wilhelm

Wien, 20

March

1912

(Vol.

5,

Doc.

375).

[45]See

Einstein to

Paul

Ehrenfest,

before

20

June

1912

(Vol.

5,

Doc.

409).

[46]For

a

discussion of Mach's

critique

and Einstein's

interpretation

of

it, see

Barbour

1992.