DOC.

6

PONDEROMOTIVE

FORCES

257

Lecture delivered to

the

Societe Suisse de Physique

(Schweizerische

Naturforschende

Gesellschaft),

Basel,

6

September

1910.

Published

in Archives des sciences

physiques et

naturelles

30

(1910):

323-324. Published

15

July

1910.

[1]"mathematique"

should

be

"magnetique."

[2]See,

e.g.,

Abraham

1905,

p. 319,

which

is

cited

in

Einstein

and

Laub

1908b

(Vol. 2,

Doc.

52),

p.

545,

as an

example

of the standard

view.

[3]The

expression

[iH]

(where

the

square

brackets denote the

vector

product)

for the

force

density on

a

current

element of

magnetizable

material

was

first

proposed by

Einstein and Jakob

Laub

in

Einstein

and

Laub

1908b

(Vol.

2,

Doc.

52).

Einstein had

already

used the

thought

experiment

described in the

following

in

a

successful

attempt

to convince Sommerfeld of this

expression, calling

it

an

"extremely

amusing

and

simple

special

case"

("überaus lustigen

und

einfachen

Spezialfall");

see

Einstein

to

Jakob

Laub, 27

August 1910,

and also Einstein

to

Jakob

Laub, 4

November

1910,

for another

comment

on

this

example.

For

a

discussion of Einstein's

and Laub's

work,

as

well

as

of its

reception

and of

subsequent developments, see

Vol.

2,

the

editorial

note,

"Einstein and Laub

on

the

Electrodynamics

of

Moving Media," pp. 503-507, in

particular pp.

506-507.

[4]The

principle

of the

equality

of action and reaction had

played

a key

role also

in

the

argument

given

in

Einstein and Laub

1908b

(Vol.

2,

Doc.

52);

see

in

particular

p.

547.

[5]The

present paper is

discussed,

e.g.,

in Gans

1911,

where

it

is

claimed

that, while

both

expressions

(1)

and

(2)

are

correct

for

special

cases,

neither of them

is

valid

in

general.

Einstein

later

expressed a

similar

view;

see

Einstein

to

Jakob

Laub,

10 August

1911.