DOC.

350

JUNE

1917 339

extended

over a

closed

curve

in

the

“Riemann foliated”

qv-space

is

now

considered.

This

integral

vanishes when the

curve can

be contracted

continuously

into

a

point

which,

owing

to

the

“Riemannization,”

is

by

no

means

the

case

for all

curves.

Now,

the

quantum

rule

requires quite simply

that

for

any

closed

curve,

ƒ

EPvdqv

=

nh

has to

apply. Epstein’s special

case

is

simply

that

each

pv

depends only

on

the

related

qv.[3]

Handsome

though

this

is,

it

is just

limited to

the

special

case

where

the

pv’s can

be described

as

(multiple)

functions

of

the

qv's.

It

is interesting

that

precisely

this limitation

removes

the

validity

of

statistical

mechanics. For

it

presupposes

that,

at

the

recurrence

of

the

qv's,

the

pv's

of

a

system

left to itself

gradually

adopt

all value

systems

compatible

with the

energy

principle.

It

seems

to

me

that

real mechanics

is

such

that the

existence

of

the

integrals

(which

preclude

the

validity

of

statistical

mechanics)

is

already

secured

by

virtue

of

its

general

foundations.

But

how to

implement

this??

I shall be

glad

to write to Onnes.[4]

Have

you seen

Nernst?

He

was

in

Hol-

land

to find out whether his

pilot

son,

who has

crashed, is

dead. The

other

died

in action

right

at

the

beginning

of

the

war.

Old Jehovah

is

still

around.[5]

Un-

fortunately He

also smites

the

innocent,

and He smites the

guilty terribly

with

blindness

so

that

they cannot feel

guilt.

So

where does

He

get

the

right

to

punish

and

crush?

Also from

force,

perchance?[6]

I

have become much

more

tolerant,

without

changing

my

views in

principle

in the least.

I

see

that

often

the

most

power-hungry

and

politically

extreme

people

could

not

kill

a

fly

as

private

in-

dividuals.

A

delusion of

epidemic proportions

is afield

which,

after

producing

immeasurable

suffering,

will

vanish

again,

so

the

generation

after

the

next

can

gasp

at

it

as

something completely

monstrous

and

incomprehensible.

I

am

very

eager

to

see

Burgers’s

new paper.[7]

You

yourself complain

again

about

yourself

and

are

not satisfied with

yourself.

Just think

how

insignificant

it

will

be

20

years

from

now

how

one

knocked

about

on

this

Earth,

provided

no wrong was

done.

It

is

all

the

same

whether

you

or someone

else

has written this

or

that

paper.

You

are

certainly

never

mindless,

except

for when

you

happen

to

be

contemplat-

ing

whether

you

are

mindless

or

not.

So, away

with

the

hypochondriac! Enjoy

yourself

with

your family

in

the

fair land of

the

living!

Affectionate

greetings, yours,

Einstein.