DOCS.

446,

447

JUNE

1913 339

446.

To

Arthur Schidlof

[Zurich,]

17

June

1913

Dear

Sir:[1]

Naturally,

I

too

have

occupied

myself intensely

with

the

question

addressed

by you,

whether the

general

radiation formula

can

be

obtained

by

the

route

currently pursued.

But it

seemed

to

me

that the

improper

therm.

equilibrium

loses its

meaning

in

the

case

of

finite

radiation

densities.[2]

Unfortunately,

serious

objections

must be

raised

against your

way

of

handling

the

problem,

only

two

of

which I shall

point

out.

1.

It

is not

permissible

to set

the radiation

density

in

the

gas

space equal

to

zero,

even

if

the

gas can

be

considered

"black,"

which

is

always possible

to achieve with

sufficiently

great

expansion.

2. The

assumption

that the

amount

of

heat

released in

the heat reservoir with

RT

2.

You

set

Pg =

a (universal

constant).

This

cannot

be

done

even

for

regular

thermodynamic

equilibrium.

Because

at

a

given

T,

I

can

still

freely

choose the

pressure

pg

of the reaction

mixture.

The

route

chosen

by you

does

not

seem

feasible to

me,

but

your

confidence

is

contagious.

Perhaps

it will

nonetheless

prove

possible

to work out

the

case

of

improper

thermodynamic equilibrium

even

for finite

radiation

density.

With

collegial greetings,

I

remain

yours,

A.

Einstein

447.

To

Jost Winteler

[Zurich,

23

June

1913]

Dear

Prof.

Winteler,

Michele left

a

few

days

ago

for

Trieste,[1]

because

he

had

to

attend

a

business

meeting.

It

is

not

certain that

he will

come back,

because he suffered here

from

a

stubborn intestinal catarrh. But

now

he

seems

to be well

again.

I

doubt

that

Michele

knows

Uncle

Paul's[2] whereabouts;

at

least

he

never

talked about

it.

But

Rosa[3]

will

certainly

be able to

give you

this

information.

Please

do

drop

in

to

see

me

if

your path

should

lead

you

to

Zurich.

I remain,

cordially,

your

Albert