348

PONDEROMOTIVE FORCES

[10]

where

we

have

put1

fIz

=

(13)

_

1(C2 +

&)

+

£ ®

+

15

®,

I

= S

V

+ j3

®

»

y X

y

Jx

y9

X

=

5

®

®

,

6X

=

•

Corresponding equations

hold for the other

two

components

of

the

ponderomotive

force.

By

integrating

(12)

over

the infinite

space,

one

obtains the

equation

[12]

(14)

Vr

=

1

IF

d&x

dr

TT

if the

field

vectors

vanish

at

infinity.

This equations states

that

on

introduction

of

the

electromagnetic

momentum

our

ponderomotive

forces

satisfy

the

law

of equality of

action

and

reaction.

Bern,

7

May

1908.

(Received

on

13

May

1908)

[11]

1Geheimrat

Wien kindly drew

our

attention

to

the fact that

H. A.

Lorentz

had

already presented

the

ponderomotive

forces for

nonmagnetizable

bodies in this

form.

Enzyklopädie

der

mathematischen

Wissenschaften 5, p.247.