2 6 0 D O C U M E N T 1 3 3 S E P T E M B E R 1 9 2 0

According to my conception, it is impossible to derive the Doppler principle

from equation

(1).[2]

In order to define radiation as a frequency , I need a wave

of the kind

is the number of waves that pass by a point in the coordinate system, while t = 1,

i.e., while a seconds clock, arranged at rest relative to this point of the coordinate

system, is making one tick. The Doppler principle results from the equation

,

whereby this equation must be made into an identity through the Lorentz transfor-

mation. I absolutely would not know how to indicate a simpler derivation of the

Doppler principle. In any case, from equation (1) nothing at all can be concluded

either about the rate of a moving clock or about the Doppler principle. You must

think of it as if t has the meaning

= time of emission of the light signal

at A

= time of arrival of the l[ight] s[ig]. at B.

There is no such thing as one clock that can indicate t.

Best regards, yours,

A. Einstein.

133. From Max Planck

Gmund on Lake Tegern, Grundner Farm, 5 September 1920

Dear Colleague,

On returning to Germany from Southern Tyrol, where no news reached me, I dis-

covered the reports about the almost incredibly disgusting behavior that had oc-

curred at the Berlin Philharmonic and about everything connected with

it.[1]

I am

momentarily at a loss for an explanation of how such baseness can be possible

among highly educated people. But of very much greater importance to me than

this problem is the issue of what impression such machinations are apt to make on

you personally and I am plagued by the thought of the possibility that you will lose

2

------

t

x y z + +

c

------------------------------ - –

.

sin

2

------

t

x y z + +

c

------------------------------ - – t

x y z + +

c

----------------------------------------- - – =

A

B

light signal

t t2 t1 –=

t1 A =

t2 B =