1 3 4 D O C U M E N T 1 9 4 J U L Y 1 9 2 1
pumped away, similar to how Wien did it with canal
in order to get them in
a vacuum.
The results of the dependence of X-ray hardness on direction can be made plau-
sible like this:
The vectorial total retardation of the electron is crucial for the direction of emis-
sion. If the electron is slowed down completely, [then] the retardation vector of the
cathode ray is directed exactly in the opposite way. The irradiated energy is mainly
emitted orthogonally to it, according to the classical theory. If the electron retains
part of its velocity, it can then fly off sideways. The vector of the total acceleration
then has, in this case, a more or less undefined direction. The concentration of the
emitted radiation around the 90° will hence, in this case, where the emitted radi-
ation is softer, be less accentuated.–
Sending you my kind regards and best wishes for your vacation time, yours,
A. Einstein.
194. To Hermann Anschütz-Kaempfe
[Wustrow, 28 July 1921]
Dear Mr. Anschütz,
Many thanks for the letter and drawing. There is no doubt that this way the mag-
net arrangement is most ideally symmetric. But we have to remember that the forc-
es become significantly larger for alternating rotor rims. According to the follow-
ing pole schemes the disturbing forces in the interior are as small as
The stabilizing effect of such an arrangement is much more favorable than in the
case of uniform rotor rims, the number of necessary Ampère windings less so.
Making it is not that hard, either.–
From the drawing sent to me it is not apparent how the eddy currents in the pole
rings are avoided. Under no condition may the iron strips form electrically closed
rings, because otherwise the fields will be choked off (induced currents that run
inside the strips parallel to the coil’s currents). The strips should actually be
arranged radially and isolated from one another. Based on the drawing it does not
look like it. I will announce our arrival and look forward to it very much.[2] Best
regards to both of you, yours,
A. Einstein.
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