DOC.

52

339

Doc. 52

ON

THE PONDEROMOTIVE FORCES EXERTED

ON

BODIES

AT

REST

IN

THE ELECTROMAGNETIC

FIELD

by

A.

Einstein

and

J.

Laub

[Annalen

der

Physik 26

(1908):

541-550]

In

a

recently published

study1

Mr.

Minkowski

presented

an

expression

for

the

ponderomotive

forces

of

electromagnetic

origin

that

act

on

arbitrarily

moving

bodies. If

one

specializes Minkowski's

expressions to

isotropic,

[2]

homogeneous

bodies

at

rest,

one

obtains for the

X-component

of the force

acting

on a

unit

volume

+

'

[3]

(1)

where

p

denotes

the

electric density,

s

the

electric conduction

current,

(B

the electric field

strength, and ©

the

magnetic

induction. This

expres-

sion

seems

to

us

not

to

be in

agreement

with

the

electron-theoretical picture

for the

following

reasons:

While

a body

traversed

by an

electric

current

(conduction

current)

experiences

a

force

in the

magnetic

field,

according

to

equation (1)

this

would not be

the

case

if the

body

in

the

magnetic

field

were

permeated

by a

polarization

current (dV/dt)

instead

of

a

conduction

current. Thus, according to Minkowski

there exists

here

a

difference in

principle between

a

displacement current and

a

conduction

current

such

that

a

conductor

cannot

be

considered

as a

dielectric with

an

infinitely

large

dielectric

constant.

In

view

of this

state

of

affairs, it

seems

to

us

that it

would

be

of

interest

to

derive the

ponderomotive

forces for arbitrary

magnetizable

bodies

on

the basis of the electron

theory.

We

present

here

such

a

derivation,

though

restricting ourselves

to

bodies

at rest.

1H.

Minkowski,

Gott.

Nachr.

(1908),

p.

45.

[1]