164

DOC.

4

THEORY

OF STATIC GRAVITATIONAL

FIELD

[29]See

Abraham

1912a,

p.

4.

This remark alludes

to

a

problem

mentioned

by

Abraham

on

p.

3,

which

was

first

pointed

out in

Maxwell

1865

(pp.

492-493):

In

a

field

theory

of

gravitation

the

field

energy

will

turn out to

be

negative

if

one

imposes

the condition that the

energy

is

zero

for

vanishing gravitational

force. For

a

contemporary

discussion of this

problem, see

Zenneck

1903,

§34.

[30]See

Planck

1906a,

1907.

[31]Hamilton's

principle

is

the

starting point

for the

gravitational theory presented

in

Einstein

and Grossmann

1913

(Doc. 13).

For further

discussion,

see

the editorial

note,

"Einstein's

Research Notes

on a

Generalized

Theory

of

Relativity,"

pp.

193-194.