DOC.

18

DISCUSSION OF DOC.

17 355

hand,

when

he

was explaining

Michelson's

experiment,

stated

outright

his

conjecture

that

it

may

well

be

good

to

assume

that

such

a change

in

length is brought

about

by

the

influence

of

the

ether

or

of molecular

forces.

These

are

two

things

that

I cannot

[6]

reconcile.

Prof.

Einstein: Allow

me

to

answer

with

a

comparison.

It

has to do with

the second

law

of

thermodynamics,

the

law

of the limited

convertibility

of thermal

energy.

If

one

takes

the

assumption

of the

impossibility

of

a perpetuum

mobile

of the second

kind

as

the

starting point

of the

argument,

then

our

law

appears

as

almost

an

immediate

consequence

of the

basic

premise

of the

theory.

But

if

one

bases

the

theory

of heat

on

the

equations

of motion of

molecules,

then

our

law

appears

as

the result of

a long

series

of

most subtle

arguments.

Just

as

here both of these

routes have

their undeniable

justification, so

the above-mentioned

points

of

view

of

Minkowski

on

the

one

hand,

and

of

H. A.

Lorentz,

on

the

other,

also

seem

to

me completely

justified.

Prof.

Meissner: As

far

as

I

know,

Minkowski

used the

theory

of

relativity

in

order

to

[7]

derive the

general equations

for

moving

bodies

from

the fundamental

equations

of the

electrodynamics

of

bodies at rest.

He

set

up

a

system

of

formulas

that

does not coincide

either

with

the formulas of

Cohn

nor

with

those of

H. A.

Lorentz.

Objections

have

been

raised

against

this

new system.

Since I know

the

whole

theory

of

relativity more

from

the

[8]

mathematical

point

of

view,

I would

very

much

like to know

the

reasons

that

prompt

the

physicists

to

decide

against

Minkowski's

equations

and

in favor

of those of Cohn and

Lorentz. It

seems

to

me,

from the mathematical

point

of

view,

that there

must exist

only

one

system

of

equations,

namely

that of

Minkowksi.

Prof.

Einstein:

If

one

starts out from

the

theory

of bodies at

rest,

then

one can

derive

only

the

laws

of

electrodynamics

for

uniformly moving

bodies

by means

of the

relativity

transformation. Do the

equations

of

electrodynamics

for

uniformly moving

bodies

also

hold

for

bodies

in

spatially

and

temporally

non-uniform

motion?

This

is

possible

but

not

certain. To that

extent,

Minkowski's

equations

are a

hypothetical

extension of those

existing

before.

Regarding

the theories of Cohn and

Lorentz,

the

following

should

be noted. The

theory

of Lorentz

deviates from

that of

Minkowski insofar

as a

small

inaccuracy

crept

into

it,

due

to

the

much

more

difficult

method of

derivation.

In

fact,

there

are no

fundamental differences between

Minkowski's

and Lorentz's

theory.

On the other

hand,

Cohn's

electrodynamics

must

be

viewed

as

fundamentally

different.

[9]

Fritz Müller:

According

to

the

explanations

given

in

the

lecture,

when

a

clock

is

set

up

at

the North

Pole,

and

a

synchronously

running

clock

is

located at the

equator,

then,

if

we

consider the rotation of the

earth,

the

clock at

the North Pole

is

at

rest,

while

the