DOC. 24 RESPONSE TO

QUESTION

BY REIßNER

281

everywhere

at

infinity,

the

guv

assume

the

values

-1

0

0 0

0-1

0 0

0

0-1 0

0 0 0

c2

where

c

is

a

constant. Furthermore,

we

chose the reference

system

in such

a

way

that

both the

system

E

as a

whole,

as

well

as

the material

point equivalent

to

it,

will be

at rest

relative

to

the reference

system,

i.e.,

that

I1,

I2,

I3,

as

well

as

I1*, I2*, I3*

vanish. Then

we

get

I4 =

/($44

+

t44)dV

I*4

=

mc.

These

two

quantites

are

to

be

set

equal

to

each

other,

where

I4

has the

meaning

of

the "rest

energy"

U0.

Hence,

m

=

U0/c.

Thus,

the inertia of

a

closed

system

E

is

completely

determined

by

its

rest

energy.

It has been shown here that the

energetic components

of the

gravitational

field

contribute

to

the

gravity

and inertia of

a

system

in

exactly

the

same

way

as

do the

energetic components

of material

structures.

(Received

on 11

December

1913)