I N T R O D U C T I O N T O V O L U M E 1 0 x l i i i
I I I
Ever since Einstein’s first visit to Leyden in 1911, his ties with its university had
been special, at first because of the presence of the much-admired Hendrik Antoon
Lorentz, and after 1912, because of Paul Ehrenfest, Lorentz’s successor. Following
their first meeting in Prague in 1912, Einstein and Ehrenfest developed a special
and lasting bond, not only as physicists, but also, and perhaps in the first place, as
kindred
spirits.[17]
In their correspondence, they discussed myriad problems in
physics, ranging from relativity theory to statistical physics and quantum theory,
kept each other informed about recent experimental investigations, and discussed
issues of foundational and philosophical concern. During his visits in Leyden, Ein-
stein grew fond of the Ehrenfests’ four children, played music with the family, and
spent time with them at the nearby seaside.
But Einstein also enjoyed the company of other Leyden physicists. He engaged
in long scientific discussions with Heike Kamerlingh Onnes, director of the cryo-
genic laboratory at Leyden, the only laboratory at the time capable of the liquefac-
tion of helium. And Lorentz remained a close scientific colleague and fatherly
friend, to whom Einstein also turned in matters of international reconciliation after
World War I.
In 1919, Ehrenfest tried to associate Einstein with the University of Leyden in a
more formal way as a full-time professor. Einstein, however, declined, on the
grounds that he could not desert his Berlin colleagues, in particular Max
Planck.[18]
Ehrenfest, Lorentz, and Kamerlingh Onnes then conceived a new plan: to create a
special chair for Einstein, with minimal obligations. As Special Professor
(bijzonder hoogleeraar) he should visit Leyden a few weeks every year to hold
some lectures. In return, he would receive a generous annual salary of 2,000 guil-
ders. The special chair would be created by the Leyden University Fund, an orga-
nization that sponsored activities at the university, such as public lectures, and that
derived its income from contributions by students, alumni, and
faculty.[19]
Initially, their plan proceeded smoothly. At its meeting of 9 February 1920, the
University Fund agreed with the proposal to create the special
chair.[20]
Lorentz ex-
pected a decision within at most a few weeks, and preparations were made for
Einstein to visit Leyden and deliver his inaugural lecture during the month of May.
Einstein completed his lecture on “Ether and Relativity,” an homage to Lorentz,
and ensured that it would be printed well in advance. Indeed, the printed version of
the lecture indicates that it was delivered on 5 May 1920 (Vol. 7, Doc.
38).[21]
But
then difficulties arose.
On receipt of requests for the appointment’s approval from the University Fund
and Leyden’s Board of Curators, the Minister of Education, Johannes Theodoor de