I N T R O D U C T I O N T O V O L U M E 1 0 x x x i
volume document in detail his sojourns in the Netherlands and the hospitality of
many Dutch colleagues. But it is his connection with Paul Ehrenfest that emerges
from the correspondence as one of the most significant and intimate bonds among
all of Einstein’s personal and scientific human ties during this period.
I
In the spring of 1914, Albert Einstein traveled from Zurich via Leyden to Berlin to
take up his new position as a permanent member of the Prussian Academy of
Sciences. By the summer of that year, Einstein and his wife, Mileva Einstein-
Maric;, had separated. Mileva returned to Switzerland with their two sons, Hans Al-
bert and Eduard, the day before the outbreak of World War I. Einstein continued to
remain in Berlin for almost two decades. During the years 1915–1920, he traveled
to Switzerland five times: he visited his sons in the summer of 1915, in the spring
of 1916—when he renewed his attempts to obtain a divorce from Mileva—, and the
summer of 1917. In early 1919, he again traveled to Zurich, where the divorce from
Mileva was finalized, and delivered a series of guest lectures on relativity at the uni-
versity. In June 1919, Einstein married his cousin Elsa Einstein in Berlin, and soon
thereafter visited with his sons and his terminally ill mother, Pauline, and lectured
again in Zurich.
The supplementary correspondence in this volume presents 149 letters written
by Einstein, mostly during the years 1916 through 1919, of which 67 addressed to
Elsa Einstein, 55 to Heinrich Zangger, and the remaining 27 to other family mem-
bers, friends, and colleagues. Einstein wrote to Elsa two series of letters and post-
cards during his trips away from Berlin in 1917 and 1919. His letters to Zangger,
who had become Einstein’s intermediary in his dealings with the Einstein family
now living in Zurich, are most numerous for 1917, a year during which Mileva Ein-
stein-Maric; was hospitalized for extended periods of time. The care of their sons
and the attendant financial arrangements appear as Einstein’s primary concerns in
these letters.
Among the 61 supplementary incoming letters for the years 1915 through 1919,
29 were written by Hans Albert and Eduard Einstein—often jointly, and sometimes
accompanying letters from Mileva—during the five years after their parents’
separation, and 12 were sent by Mileva in 1918, the final year of the marriage.
These letters complement the extant correspondence already published in previous
volumes, which contained 32 letters to Mileva and 34 letters to the boys written by
Einstein during this same period.
The supplementary family correspondence also documents the involvement in
family matters of Einstein’s sister, Maja Winteler-Einstein, of her husband, Paul