282

DOCS.

294,

295 FEBRUARY

1917

294. To Paul

Ehrenfest

[Berlin,]

4 February

1917

Dear

Ehrenfest,

The

paper by

Mr.

Burgers delighted me.[1]

The

adiabatic method and the

Schwarzschild-Epstein

method

now

mutually

support

each

other.[2]

It

is

a

fine

success;

the

paper

is

also

very well

written.

I

have

perpetrated

something again

as

well

in

gravitation

theory,

which

exposes

me a

bit

to

the

danger

of

being

committed

to

a

madhouse.[3]

I

hope

there

are none over

there

in

Leyden,

so

that

I

can

visit

you again

safely.

It

is

a

pity

that

we

do

not live

on

Mars

and

just

observe man’s nasty antics

by

telescope.

Our

Lord

Jehova

no

longer

needs to

send down showers of ash and

brimstone;

he has modernized and has

set

this

mechanism to

run on

automatic.

Cordial

greetings, yours,

Einstein.

295. From Max Planck

Grunewald,

4 February

1917

Dear

Colleague,

Now

that

I

have

gained

a

bit

more

clarity

on

the

dynamic significance

of

the Jacobian

action

integrals,

I

would

like

to

report

on

it to

you.[1]

Let

E

be

the

energy

as a

function

of

the

coordinates

q1, q2,

...

and of the

momenta

p1, p2,

...;

and

if

we

set

in

this

function

dW

Pl

dqi

dW

(1)

the Hamilton-Jacobi

differential

equation

is then:

dW

dt

+

E

=

0.

The

same

is

satisfied

by

W

=

-a1\t +

V,

where

V is

a

function of

q1,

q2,

...

and

of

the

constants

a1, a2,

...,

among

which

the

first

a1

represents

the

value for

E.

Then

the

2n motion

equations are, first,

equations

(1);

second,

the

equations:

dW

da

i

dV

dai

=

ßu

dw

da2

=

-t

+

(2)