1 3 2 D O C U M E N T 1 9 2 J U L Y 1 9 2 1
With gratitude and heartiest best wishes to you and Mrs. Einstein, faithfully
yours,
Morris R. Cohen
Translator’s note: Original written in English.
191. From Hermann Anschütz-Kaempfe
Kiel, 24 Bismarckallee, 23 July 1921
[Not selected for translation.]
192. From Lise Meitner
Dahlem, Berlin, 63 Thiel-Allee, 24 July 1921
Esteemed, dear Professor,
I fear you will think very badly of me for answering your friendly, interesting
letter[1]
only today. But I knew that Mr. Geiger is engaged in a
research[2]
that
touches on the questions you raised, and so I wanted to speak with Mr. Geiger first
before writing you. And this was not possible for me sooner.
There aren’t yet any quantitative analyses on the relation between the magnitude
of deflection and the consequent loss in velocity. It has just been qualitatively
established that the more strongly deflected -rays (to my knowledge no such anal-
yses have been done on cathode rays) experience larger losses in velocity than the
more weakly deflected ones. Yet these experiments are always conducted with rel-
atively thick foils, so the deflections surely always represent summation effects and
not individual deflections of one
atom.[3]
As Mr. Geiger tells me, this is also where
the main difficulty lies, namely, such thin foils as would have to be used with cath-
ode rays, because of the low attainable velocity, cannot be produced, and for -rays
the intensities are also so low that one cannot measure them at larger deflection
angles. Mr. Geiger is engaged in determining the dependence of the scattering of
-rays (quite homogeneous rays are screened out by a magnetic field) on the thick-
ness of the scattering foil and the atomic number used, i.e., for a certain thickness
he measures the most probable angle of
deviation.[4]
As he told me, though, he has
not yet surpassed 10° (he is using Au foils of
10–5
cm thickness), because he fails
at the weaker intensities. If he were to succeed in overcoming this difficulty, he
would, of course, also be able to examine the problems of interest to you, whether