x x x I N T R O D U C T I O N T O V O L U M E 1 0
written by Einstein between April 1916 and October 1919, mainly in the form of
postcards, is addressed to Elsa Einstein, from whom no letters are extant for these
years, most likely because, as early as April 1912, Einstein had promised to “al-
ways destroy” Elsa’s letters (see Vol. 5, Doc. 389). The second largest group of
newly available letters written by Einstein is addressed to Heinrich Zangger.
This supplementary correspondence with members of his families in Zurich and
Berlin, as well as with Zangger, complements the family correspondence already
published in previous volumes. Together, this material provides the reader with a
much richer and fuller picture than we have had to date of Einstein’s personal life
and the many hardships and deprivations Einstein and his family members faced
during the years of World War I and its aftermath: illnesses, malnutrition, financial
worries, separation, divorce, and remarriage.
In addition, the supplementary correspondence also includes nine letters written
in 1909 and 1910 by Einstein to the mathematician Vladimir Varic;ak, with whom
Einstein had a published dispute in 1910 on the reality of relativistic length
contraction (Einstein 1911f [Vol. 3, Doc. 22]). Varic;ak was interested in an inter-
pretation of relativity theory in terms of Lobachevsky’s geometry. The letters by
Einstein deal with the problem of a relativistic definition of rigid bodies and its in-
tricacies for non-uniform and rotational motion.
The family correspondence presented in the second half of this volume contains
new information on Einstein’s personal life during the last eight months of 1920,
such as his first vacation with his sons in southern Germany and his renewed at-
tempts to move his Zurich family there. The few letters by Elsa Einstein reveal her
own perspective on her relationship with Einstein.
The second half of the volume also offers insight into specific scientific issues
that Einstein focused on during this period, his associations with fellow physicists
in Europe (most notably in Germany and Holland) and, by degrees, also in the Unit-
ed States, and his lectures on the special and general theories of relativity within
Germany and during his trips to Holland, Denmark, and Norway. The documents
shed new light on the challenges Einstein faced as a result of his recently acquired
celebrity status, and his subsequent entrance into the public arena, primarily
through a series of increasingly acrimonious attacks directed at relativity. We learn
of Einstein’s own reactions to these new aspects of his career, as well as those of
his family members, his close circle of friends, his colleagues, and, for the first time
on a larger scale, of the general public. They illustrate the evolving popular percep-
tions of science and the scientific community in Germany and beyond.
The successful completion of the intricate process of Einstein’s appointment as
Special Professor at the University of Leyden led to his well-known inaugural lec-
ture on “Ether and Relativity” in October 1920. The letters contained in the present