DOCUMENT 128 NOVEMBER 1908 149

Atherwirbeltheorie der

Materie,

in welcher Äther und Materie

wesensgleich

sind,

am

ehesten

zum

Ziel

führt.[14]

Dieses Bild muß dann

vor

allem

die

De-

formation

erklären,

die ein Ätherwirbel durch Translation erfährt. Die Poin-

caresche

Hypothese

eines Atherdrucks würde dann

aus

dem Atherbilde her-

aus zu

erklären

sein.[15]

Das scheint mir sehr schwer

zu

sein. Der einstweilen

gewonnene Standpunkt,

daß

man

rein

phänomenologisch

alles berechnen

kann,

ist schon ein

großer

Gewinn.

Mit freundlichen Grüßen Ihr

ergebener

A. H.

Bucherer

ALS.

[6 193].

[1]See

Docs.

117

and

119

for

more on

Bucherer's work

on

Becquerel rays.

[2]Bucherer 1908b,

which

was

presented

22

September

at

the 80th

meeting

of the Gesell-

schaft Deutscher Naturforscher und Ärzte

in Cologne.

[3]Probably

Einstein

1906e.

[4]The argument

that follows

is

also contained in Bucherer

1909,

pp.

535-536.

[5]The

square

brackets

in

the

following equation

are

in

the

original

and denote the

vector

product.

[6]H.

A.

Lorentz;

see

Lorentz

1895,

pp.

24-26.

A copy

of

Lorentz

1906-a

reprint

of

Lorentz

1895-with

"Zangger"

written

in Zangger's

hand

at

the

top

of the title

page, is in

Einstein's

personal library.

[7]In

the

preceding

expression

v

is

the

speed

of

light.

[8]A

"Tensortripel" corresponds to

what

is

now

known

as a

three-dimensional

symmetric

tensor.

The

term

was

first introduced

by

Woldemar

Voigt

(see

Voigt

1898, §2).

[9]On

pp.

27-28 of

Lorentz 1895

the

problem

of

stresses

in

the

ether is discussed. Lorentz

calculates the Maxwell

stresses

on a

volume of free ether and shows that

in general

these

stresses do

not

vanish and should

set

the volume into motion. Since the ether

is

taken

to

be

immobile

as a

whole,

there

is

a

contradiction,

which

is

then cleared

away

by

the

assumption

that it

is

meaningless

to

speak

of forces that work

on

the

ether.

This

implies

that for the ether

the

principle

of action and reaction does

not

hold. For this conclusion Lorentz

was

criticized

by

Henri Poincare

(1854-1912) (see

Poincare

1900).

The introduction of the

concept

of elec-

tromagnetic

momentum

offered

a

way out

of

these difficulties. See Miller

1981,

sec.

1.7,

for

a

historical review.

[10]See

Planck

1908a, in

which Planck extends the

concept

of

momentum

beyond

mechan-

ics and

electrodynamics

by

arguing

that for

every

energy

flow

there exists

an

associated

mo-

mentum

which

is

found

by dividing

the

energy

flow

by c2.

A

momentum

flow is

also connected

with this

momentum.

[11]The

80th

meeting

of the Gesellschaft Deutscher Naturforscher und Ärzte

was

held from

20

until

26

September

in

Cologne.

[12]"Elektromag"

is

underscored

in red,

but

part

of the red line

(underneath

the letters

"ktro") is

deleted in

pencil.

[13]Cf.

Einstein's

comments

on

the

desirability

of

founding special relativity

on

basic ele-

ments

in

Doc.

73.

[14]See

Whittaker

1951,

pp.

293-303 for

a

review of theories of

vortex atoms.

[15]See

Poincare 1900 for Poincare's

hypothesis.