THE FIELD EQUATIONS OF GRAVITATION 24!ularly take them on holiday trips. These contacts were not always easy, since
Mileva never reconciled herself to the separation and subsequent divorce. In later
times, after Einstein's remarriage, the sons would visit and stay with their father
in Berlin.
Soon after the separation, Einstein moved into a bachelor apartment at Wit-
telsbacherstrasse 13. Early in April he wrote to Ehrenfest, 'It is pleasant here in
Berlin. A nice room ... my relations here give me great joy, especially a "Cousine"
[female cousin] of my age to whom I am attached by a long friendship' [E8]. A
year later he told Zangger, 'Concerning my personal circumstances, I have never
been as peaceful and happy as I am now. I live a retiring life, yet not a lonely one
thanks to the loving care of a "Cousine" who in fact drew me to Berlin' [E9].*
We shall hear more about this cousin in Chapter 16.
By the time Einstein arrived in Berlin, he was already a man of great renown,
though not yet the stellar figure he was to become five years later. It was therefore
natural that soon after his arrival, he would be approached by the editors of Die
Vossische Zeitung, a major German daily newspaper, with the request that he
explain something of his work to their readers. Einstein accepted. On April 26,
1914, his first newspaper article appeared, entitled 'Vom Relativitatsprinzip,'
About the relativity principle [E10]. It is nicely written and deals mainly with
topics in the special theory. Its last paragraph begins with the question, 'Is the
[special] relativity theory sketched above essentially complete or does it represent
only a first step of a farther-reaching development?' Einstein remarked that the
second alternative appeared to him to be the correct one but added that 'on this
point, the views even of those physicists who understand relativity theory are still
divided.'**
This divergence in views on the future of relativity theory, characteristic for the
period 1913-15, was much in evidence on the occasion of Einstein's inaugural
address before the Prussian Academy, on July 2, 1914 [E12]. After expressing his
gratitude for the opportunity given him to devote himself 'fully to scientific study,
free of the excitements and cares of a practical profession,' he turned to the major
current issues in physics. He spoke in praise of Planck, whose 'quantum hypoth-
esis overthrew classical mechanics for the case of sufficiently small masses moving
with sufficiently small velocities and large accelerations.. .. Our position regard-
ing the basic laws of these [molecular] motions is similar to that of the pre-New-
tonian astronomers in regard to planetary motions.' Then he went on to relativity
theory and observed that the special theory 'is not fully satisfactory from the the-
oretical point of view because it gives a preferred position to uniform motion.'
Planck replied [PI], welcoming Einstein and remarking, 'I know you well
enough to dare say that your real love belongs to that direction of work in which
*'... die mich ja uberhaupt nach Berlin zog.'
**A 1915 review of relativity theory by Einstein [Ell] has the same tenor as his newspaper article.
It is almost entirely devoted to the special theory and toward the end contains phrases nearly identical
to the ones just quoted.