1 4 4 D O C U M E N T 2 1 3 A U G U S T 1 9 2 1
such a lack of principle. In an exchange of letters with Bohr (whom I am now unfor-
tunately not visiting as
because he is still quite overworked), we hap-
pened to discuss the effect described by Klein–Rosseland in the Z[ei]tschr[ift] für
which, as you know, exists as an extension of your considerations on the
equilibrium between radiation and translational energy of
Klein and Ros-
seland say that an electron at low velocity could gain kinetic energy upon collision
with an excited electron in such a way that although the excited atom returns to its
normal quantum state without radiating, the electron also receives as kinetic energy
the whole quantum that otherwise occurs as radiation. Now, Bohr upheld the view
that such an emergence of translational energy was possible even for a collision
between a normal atom and an excited atom, at the expense of radiative energy, and
that the extinction of resonance fluorescence at higher gas pressures could be
explained in this way. According to preliminary experiments, this appears at least
not to be impossible. So a question occurred to me whether this effect, which rep-
resents a transfer of radiative energy to the translational motion of
not open an opportunity to avoid the conclusions about needle
radiation.[5] Born[6]
and Bohr had doubts about whether an equilibrium between radiation and transla-
tional energy could be reached if one moves to low pressures, which then could
make the ratio between direct radiative processes to the number of such collisions
very small. But I have the impression that one could perhaps circumvent this prob-
lem, since the collisions between the atoms would also become very rare at low
pressures. At diminishing pressure, ever longer periods of time would have to
elapse for the equilibrium to set in, wouldn’t it? It would please me very much if
you would let me know by postcard, without the reasons, whether this consider-
ation is complete nonsense. Additionally, I would very much like to ask whether
you will be in Berlin at the end of September or early October, respectively,
because I wanted to come to Berlin sometime during that period and, if I may, look
you up. Please don’t be cross with me for this disturbance.
With most cordial greetings, yours very truly,
J. Franck.
213. From Jakob Grommer
Göttingen, 18 Planck St., 25 August 1921
Dear Prof[essor],
How are you? I read your lecture at Blütner Hall with great
summer I am doing somewhat better, t[hank] G[od]. Here I have essentially been
working on the th[eory] of rel[ativity]. I am already writing the book about
Previous Page Next Page