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university in Jerusalem in receiving its rightfully legitimate property—most
incomprehensible of all, if this came from the Russian government, famed for its
interest in the advancement of the cultures of the rising nations of the East. The de-
velopment of the university in Jerusalem, and quite especially of its branches di-
rected at researches on the East, is being followed with most avid interest by men
of science and of intellectual progress in all countries. I confidently rely on the
hope that the Russian government appreciates the importance of this enterprise to
the fullest degree and that it will extend its good will to the library of the university
in Jerusalem.
In expression of my utmost respect,
A. Einstein
404. From Albert Wigand
Halle-on-S[aale], 9 Kohlschütter St., 23 December 1924
Esteemed Professor,
Since our conversation on Dec.
I have thoroughly rechecked whether in the
aircraft experiments the aircraft’s self-charge or the deformation of the Earth’s field
around the aircraft can simulate an excess in the ion content of one sign, be it by
disturbance in the ion distribution in the approaching airflow, or by an alteration in
the paths of the ions entering into the precision capacitor. One can, of course, ap-
proximately calculate this (as has already been done by
for observations
on the ground), and it yields that the air speed in the aircraft of 30 m/sec is large
against the maximally presumable ion velocities, so that the ion distribution in the
approaching airflow, as well as the paths of the entering ions, remains practically
unchanged. At most, it can involve an influence of a few percentages, whereas the
excess in positive charge over the negative charge, measured by me at 5 km altitude
in the aircraft, comes to 20% of the mean of both.
It is therefore not to be expected that trials with variation in the flow velocity will
have a positive outcome, as one still has to reckon with temporal fluctuations of
many percentages in the ionization, between one trial and the following one. And
even if one did let two identical instruments operate at the same time next to each
other under variable conditions, the deviations of a few % would fall within the
margin of error and the range of local variations. Thus, I do not intend to perform
such trials but rather want to try to attain definite results in another direction, as we
have recently already discussed. My earlier trials at varying the aspiration velocity,
which I recently spoke about, were performed in the laboratory, hence without any
self-charge of the apparatus and without an external field, in order to test the pres-
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