EINSTEIN'S COLLABORATORS 485stein was quite excited about his invention, and at one time must have even con-
sidered patenting it. 'I am very curious how much can be achieved—I have rather
high hopes. I have dropped the patent, mainly because of the lack of interest of
the manufacturer [?]' [E4]. A few months later, he published his proposal [E5]
and in 1908 tried to construct his own Maschinchen [E6]. In 1910 the Habicht
brothers published the results of experiments 'performed together with A. Einstein
at the laboratory of the University of Zurich,' in which Einstein's idea was real-
ized with the help of a set of six rotating condensers [H2]. Einstein still continued
to take a lively interest in the project after his own work had gone in other direc-
tions. In 1911 [E7] and again in 1912 [E8], he wrote from Prague to Besso about
the great success Paul had had in demonstrating the apparatus in Berlin.
Rapid advances in amplification technology overtook Einstein's design, how-
ever. After Paul's death in 1948, Einstein wrote to Conrad, 'The memory awakens
of old days in which I worked with your brother on the ... little machine.... It
was wonderful [Schon war es], even though nothing useful came of it' [E9].- Ludwig Hopf. b. 1884, Niirnberg. PhD with Sommerfeld in 1909. Hopf
met Einstein in September 1909 at the Salzburg physics meeting and soon joined
him at the University of Zurich as his assistant. Together they wrote two papers
on classical statistical aspects of radiation, including the problem of the motion of
a resonator in a radiation field [E10, Ell]. Hopf arranged a meeting between
Einstein and Carl Jung, the psychoanalyst [SI]. In 1911 Hopf accompanied Ein-
stein to Prague. Later that year he accepted an assistantship at the Technische
Hochschule in Aachen, where he eventually became a professor in hydrodynamics
and aerodynamics. He did important work in these fields, contributed to the
Handbuch der Physik [H3], and was co-author of a highly esteemed textbook on
aerodynamics [Fl]. He lost his position at Aachen in 1934 because he was a non-
Aryan. Soon thereafter he moved to Dublin as professor of mathematics at Trinity
College, d. 1939, Dublin. - Emil Nohel. Assistant to Einstein in Prague. Nothing is recorded about
him in the literature except for a few brief comments in the biography by Philipp
Frank: 'Nohel... was the son of a small Jewish farmer, and as a boy he walked
behind the plow. He had the quiet poise of a peasant rather than the nervous
personality so often found among the Jews. ..' [F2]. I am grateful to Y. Nohel
from Haifa for providing me with more details about his father. With his per-
mission, I quote from his letter to me [Nl].
Emil Nohel was born in the small Czech village of Mcelly, the son of a farmer.*
He received a German education in Prague, where he entered the German Uni-
versity in 1904. Anton Lampa, the professor of experimental physics in Prague,
advised the young student not to take physics as a main subject 'since all the orig-
inal work had already been done, the laws had been established, and important
new developments were not be be expected.' Nohel therefore took mathematics as
*In the 1860s, it became legal for Jews to acquire land in that region.