378 DISCUSSION

OF

SZARVASSI

Doc. 59

"Discussion"

following

lecture

version

of

Arthur Szarvassi,

"The

Theory

of

Electromagnetic Phenomena

in

Moving

Bodies

and

the

Energy

Principle"

[Physikalische

Zeitschrift

10

(1909):

813]

[1]

Einstein:

I

think that

a body

subjected to

some

forces, that this

body,

when

observed

from

a

relatively

moving

coordinate

system,

because

of

its

being

[2]

subjected to

forces,

represents

an

energy.

If

this

assumption

is

not made,

there

will

arise

a

violation

of

the

energy

principle. Don't

you

think

that

this

may

be

the basis

of the

example

you

considered? Is it clear

to

you

what

I

mean?

Lecturer:

Not completely.

Einstein: It

can

be

shown

that

a moving body

subjected to

forces

whose

resultant

does

not

vanish,

in certain

cases

does

not get

accelerated

thereby.

One

must

therefore

assume

in

the

theory

of

relativity that

the

moving

(rigid)

body

subjected to

forces

possesses

a

certain

energy

content;

otherwise,

one

gets

a

violation

of

the

energy

principle.

Lecturer:

That

would

mean

that,

besides the

so-called kinetic

energy

in

the

currently

accepted

sense,

and

besides the so-called usual

potential elec-

tric

energy

of

the

system,

there exists

an

additional part

of

energy.

Because

I

made

no

assumption

about the

quantity

v,

the

above

part

would

have

to

be

contained

in

this function. After all,

I

did

not

say

anything

about the

form

[3] of

the function

v.

The

energy

equation

expresses

the

energy

principle quite

generally.

It is

very

likely

that this

energy

quantity

is

contained

in

v.

Einstein: I

cannot comment

on

that, because

I did

not enter

suffi-

ciently

into the

spirit

of

this consideration.