DOCS.

151-153

APRIL-MAY

1909 107

151.

To

Conrad Habicht

[Bern,

28

April

1909][1]

I

am

now

quite

sure

about the

position

at the

University

of

Zurich.[2]

152.

From

Ayao

Kuwaki

Cambridge,

2

May

1909

Esteemed Doctor Einstein:

I take the

liberty

of

sending you my

best

regards

from the

famous

old

Engl, university

town. I met

with Mr. Solbine in

Paris.[1]

But

to

my

regret

I could not meet with him

often because

my

time

was

limited. I

plan to

stay

a

few

days

here

in

Cambridge

and

then

to return to Berlin. Please

give my

best

regards

to

your

wife and

your

daughter.[2]

Yours

very truly,

Ayao

Kuwaki

153.

From

H.

A.

Lorentz

Leiden, 6

May

1909

Highly

esteemed

Sir,

Please

do

forgive

me

for

answering your

kind

letter[1]

only

now; I

was

rather

busy

and

had

to

wait

for

a

quiet

day.

First of

all,

let

me

say

something

in

reply

to

your

postcard.[2]

It

is

very

kind

of

you

to

have such

a

favorable

opinion

about

my

theory[3]

that

I expounded

in

my

lecture in

Rome,

but

it has

turned

out

that

it has

a

weak

side

after

all.

Namely,

Mr.

van

der

Waals

Jr.[4]

has

made the remark that

my

conclusions

are

valid

only

if

one

ascribes

a

material

mass

to

the

electrons.[5]

Otherwise the

equations

of motion of

an

electron reduce

to

the

assertion that the total

force

acting

upon

it

is

zero;

the

equations

of motion

no

longer

contain the accelerations of

the

electron but

only

its velocities.

Actually,

from

the

general

formulas that

I have

developed,

it

is

indeed

possible

to

derive

3n

equations

(if n

is

the number of

electrons)

from which

the accelerations

have

totally

disappeared;

one can imagine

that,

by means

of these

equations,

all the

q2

are

expressed

in terms

of the

q

and

the

q3)[6]

But

under these

circumstances

it

is

impossible

to

construct

a

"canonical ensemble" that

is

based

upon

the

coordinates

q

and all

the

q,

or

the momenta

corresponding

to them,

as

independent

variables.

Mr.

van

der

Waals

expressed

his

hope

that,

with this

circumstance taken

into

consideration,

it

might

eventually

be

possible

to derive

a

correct

radiation

formula

without

abandoning

the usual

basic

assumptions

of the

electron

theory.