42

DOCS.

57,

58

SEPTEMBER

1907

As for

the

rest,

it

seems

to

me

that

the

question

as

to

what

happens

with

these

small

energy

quanta

in the

absorbing

body

is not

yet

ripe

for

an answer.

If

one

takes the

theory

of

light

quanta

as a

basis and

assumes

that

only

finite

energy quantities

can

be

absorbed,

then

one

must

regard

the

exponential

law

of

absorption

as

approximately

valid

only

for

relatively large energies,

and

abstain

from

any answer

to

the

question

as

to what

happens

with

the

small

ones.

Finally,

I

wish also

to

tell

you

that

I cannot uphold

§7

of

my

paper,[3]

at

least

not

the second

part

of

it.

It

contains

an error

that

is

closely

linked

with

some

ideas about

Planck's

hypothesis

of natural

radiation,[4]

which

I

will describe to

you

one

of

these

days.

Upon

my

return

I

came

across an

article in

the

Annalen

by

J. Laub,

"Optics

of

Moving

Media,"[5]

which derives

the

dragging

coefficients[6]

from

the

relativity principle.

The

paper

has

a

very

neat basic

idea, but, unfortunately,

it

later

on

contains

two

direct

errors

and

one inconsistency

in

the

reasoning,

namely an

interchanging

of

group

and

phase

velocity.[7]

Even

so, I

did

not

withdraw

my derivation;

rather,

it will

appear

in

one

of

the

next

issues.[8]

I have

communicated

my objections

to

the

author.[9]

At

the

moment I

am

absorbed

with

a new

article

by

J. J.

Thomson,

"On

the

Electrical

Origin

of

the

Radiation

from

Hot

Bodies"

(Phil.

Mag.

14:

217),[10]

which

is

very

interesting,

even

though I

disagree

with

it,

because for

the

time

being I

cannot

believe

that the

manner

in which

electrons

get

accelerated

in collisions with atoms

is

the

same

for all bodies.

Rest assured that

I

will

take

advantage

of

the

next

opportunity

that leads

me

to

the

vicinity

of Bern

to

look

you up.

The

stimulating suggestions

that

I

got

from

my

conversation

with

you

are so

valuable

that

I would like to have

more

of

them.[11]

Please

mention

me

to Mrs.

Einstein.

With

kindest

regards,

your

M.

Laue

58. To Johannes

Stark

Bern, 25 September

1907

Highly

esteemed Professor

Stark:

I will be

glad

to

furnish

the

report

for

the Jahrbuch that

you

requested,

only

please

apprise

me

of the

approximate

date

you

would like

to

get

it.[1]

I must

also note

that

I

am

not

in

a

position

to

acquaint

myself

with

everything

published

on

this

topic,

because

the

library

is

closed

during

my

free

time.[2]

In

addition

to

my own

works,

I

am

acquainted

with

one

paper

by

H. A.

Lorentz

(1904),[3] one by

E.

Kohn,[4]

one by

Mosengeil,[5]

and

two

by

Planck.[6] I

do not know

of

any

other theoretical

papers

on

the